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 European Extratropical Cyclones
IMPLICATIONS FOR LOCAL INSURERS
0 European Extratropical Cyclones | TransRe White Paper
by James Rohman | May 2014
!
2
1
!
Introduction
"
2
1"
This paper highlights the climatology, characteristics, history and
climate change projections of European Extratropical Cyclones.
"
January 2014" was the fourth warmest since record keeping began in 1880,
yet it fell in the middle of the most extreme winter Europe (and the Northeast
US) has experienced in 15 years. A nexus of storms brought high winds,
heavy rainfall and severe snowstorms for almost five months, causing
flooding and damage to life onshore and at sea.
Such prodigious weather patterns indicate equally prodigious climate
disturbances. Many of those storms formed as Extratropical Cyclones
3 section of this paper discusses the large-scale climate
(ETC). The first
variations and indices that encourage and energize ETC development.
4
"
Every year, roughly
200 atmospheric disturbances form in the North
3
Atlantic. A handful of the disturbances, which develop as cold-core and
asymmetric cyclones, morph into organized storms and track east towards
Europe. The second
section summarizes the characteristics and dynamics
"
of these pandemonium-inducing windstorms.
4"
"
On average, European ETCs create $1.2 billion of insured loss per year.
In extreme years with multiple tail events, they can be the leading cause of
global storm losses; in 1990 and 1999, they caused $18 billion and $14
billion of insured losses, respectively. The 2014 season is expected to
exceed $5.5 billion in insured loss. Section three covers the finer points of
the European ETC archival record.
5
ETCs that form in the North Atlantic are among nature’s most powerful
cyclones on earth, deriving their energy from the interaction and difference
between cold Arctic air masses and warm subtropical air masses. ETCs can
5 " with central low pressure as low as 916 mb, winds up
produce storms
to 140 mph and wave heights over 100 feet. Given the recent record of
IPCC reports and extreme weather, the final section offers predictions for
"
ETC development
and tracking.
6
6"
"
The disruption and loss to everyday life from extreme weather is
calamitous. As the science of climatology continues to evolve, TransRe
strives to inform the insurance industry of advancements in the field. Our
efforts come with the hope that property damage, loss of life and societal
interferences will diminish with greater knowledge of extreme natural
catastrophes.
Figure
1. An extratropical disturbance turns into an organized storm in the eastern
North Atlantic. Over February 12-14, 2014, a series of storms struck the coastline of
northern Europe, causing widespread flood and damage, resulting in approximate
insured losses of $1.3B to residences, businesses and infrastructure.
Figure 1. An extratropical disturbance turns into an organized storm in the eastern
North Atlantic. Over February 12-14, 2014, a series of storms struck the coastline of
northern Europe, causing widespread flood and damage, resulting in approximate
insured losses of $1.3B to residences, businesses and infrastructure.
#!
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European Extratropical Cyclones | TransRe White Paper
3 European Extratropical Cyclones | TransRe White Paper
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European Extratropical Cyclones | TransRe White Paper
1
#!
Executive Summary
•
Extratropical Cyclones (ETC) that form in the North Atlantic are, on
average, the second most destructive insured natural catastrophe
worldwide (after Atlantic hurricanes).
•
They can generate winds up to 140mph and waves over 100ft.
•
The wind-fields range from 120-1200 miles, with the spread of most
damaging winds 50-150 miles from the storm center.
•
On average, 200 ETCs form each year.
•
They derive their energy from the horizontal temperature difference
between warm, subtropical air masses and cold, polar air masses.
•
The two most consistent factors driving European ETCs are the
Arctic Oscillation (AO) and North Atlantic Oscillation (NAO).
•
AO and NAO shape the jet stream, funnel ETCs into various parts
of Europe.
o
Positive AO/NAO is associated with storms that have a
west-southwest to east-northeast track across Europe.
o
Negative AO/NAO is linked to a more south-to-north track.
o
NAO positive (negative) years are associated with a 1015% increase (decrease) in losses during winter storm
seasons.
•
AO/NAO variation is linked to the dynamics of the Madden-Julian
Oscillation (MJO), a global tropical weather anomaly.
•
Climate projections indicate an increase in ETC wind gusts from the
eastern North Atlantic Ocean into Northern and Central Europe.
•
Three futuristic climate simulations show ETC frequency is
expected to increase over many parts of Europe, from Scandinavia
to the Adriatic, due to climate change.
•
In addition to land based losses, ETCs will impact marine
exposures. Post-Panamax containerships are more prone to a
phenomenon known as ‘parametric rolling’ than smaller vessels
due to hull shape.
•
TransRe is working to support insurers to better understand the
causes and implications of European Extratropical Cyclones.
2 European Extratropical Cyclones | TransRe White Paper
2
Introduction
Introduction
This paper highlights the climatology, characteristics, history and
This
paper change
highlights
the climatology,
characteristics,
history
and
climate
projections
of European
Extratropical
Cyclones.
climate change projections of European Extratropical Cyclones.
January 2014 was the fourth warmest since record keeping began in 1880,
January
the fourth
warmest
since record
keeping
in 1880,
yet it 2014
fell in was
the middle
of the
most extreme
winter
Europebegan
(and the
Northeast
yet US)
it fellhas
in the
middle of the
most
extreme
winter
Europebrought
(and the
Northeast
experienced
in 15
years.
A nexus
of storms
high
winds,
US)heavy
has experienced
15 years.
A nexusfor
of almost
storms five
brought
highcausing
winds,
rainfall and in
severe
snowstorms
months,
heavy
rainfall
and
severe
snowstorms
for
almost
five
months,
causing
flooding and damage to life onshore and at sea.
flooding and damage to life onshore and at sea.
Such prodigious weather patterns indicate equally prodigious climate
Such
prodigious weather
indicateformed
equallyas
prodigious
climate
disturbances.
Many ofpatterns
those storms
Extratropical
Cyclones
disturbances.
Many
of
those
storms
formed
as
Extratropical
Cyclones
(ETC). The first section of this paper discusses the large-scale
climate
(ETC).
The first
section
ofthat
this encourage
paper discusses
the large-scale
climate
variations
and
indices
and energize
ETC development.
variations and indices that encourage and energize ETC development.
Every year, roughly 200 atmospheric disturbances form in the North
Every
year, roughly
atmospheric
disturbances
form
the North
Atlantic.
A handful200
of the
disturbances,
which develop
asincold-core
and
Atlantic.
A handful
of the morph
disturbances,
which develop
as cold-core
and
asymmetric
cyclones,
into organized
storms and
track east
towards
asymmetric
cyclones,
morph
intosummarizes
organized storms
and track east
towards
Europe. The
second
section
the characteristics
and
dynamics
Europe.
The
second
section
summarizes
the
characteristics
and
dynamics
of these pandemonium-inducing windstorms.
of these pandemonium-inducing windstorms.
On average, European ETCs create $1.2 billion of insured loss per year.
On In
average,
create
$1.2 billion
of insured
loss per
year.of
extremeEuropean
years withETCs
multiple
tail events,
they can
be the leading
cause
In extreme
years
with
multiple
tail
events,
they
can
be
the
leading
cause
of
global storm losses; in 1990 and 1999, they caused $18 billion and $14
global
storm
losses;
in
1990
and
1999,
they
caused
$18
billion
and
$14
billion of insured losses, respectively. The 2014 season is expected to
billion
of insured
losses,in
respectively.
TheSection
2014 season
is expected
topoints of
exceed
$5.5 billion
insured loss.
three covers
the finer
exceed
$5.5 billion
in archival
insuredrecord.
loss. Section three covers the finer points of
the European
ETC
the European ETC archival record.
ETCs that form in the North Atlantic are among nature’s most powerful
ETCs
that form
the North
Atlantic
are among
most powerful
cyclones
on in
earth,
deriving
their energy
fromnature’s
the interaction
and difference
cyclones
on earth,
deriving
their energy
from the
interaction
difference
between
cold Arctic
air masses
and warm
subtropical
air and
masses.
ETCs can
between
cold
Arctic
air
masses
and
warm
subtropical
air
masses.
ETCs
canup
produce storms with central low pressure as low as 916 mb, winds
produce
storms
with
central
low
pressure
as
low
as
916
mb,
winds
up
to 140 mph and wave heights over 100 feet. Given the recent record of
to 140
mph
and and
wave
heightsweather,
over 100
theoffers
recent
record of for
IPCC
reports
extreme
thefeet.
finalGiven
section
predictions
IPCC
reports
and extreme
weather, the final section offers predictions for
ETC
development
and tracking.
ETC development and tracking.
The disruption and loss to everyday life from extreme weather is
Thecalamitous.
disruption and
loss
to everyday
life from
extremetoweather
is
As the
science
of climatology
continues
evolve, TransRe
calamitous.
the the
science
of climatology
continues
to evolve,
TransRe
strives to As
inform
insurance
industry of
advancements
in the
field. Our
strives
to inform
the insurance
industry
of advancements
Our
efforts
come with
the hope that
property
damage, lossinofthe
lifefield.
and societal
efforts
come
with
the
hope
that
property
damage,
loss
of
life
and
societal
interferences will diminish with greater knowledge of extreme natural
interferences
will diminish with greater knowledge of extreme natural
catastrophes.
catastrophes.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
3 3 3
The Science of European Extratropical
The Science of European Extratropical
Cyclones
Cyclones
Climatology
Climatology
The major factors driving European ETCs are the Arctic Oscillation and
The major factors driving European ETCs are the Arctic Oscillation and
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
Arctic Oscillation (AO)
Arctic Oscillation (AO)
The Arctic is home to a semi-permanent low pressure circulation
The Arctic is home to a semi-permanent low pressure circulation
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
of 2014. The Vortex is in constant opposition to (and therefore represents
of 2014. The Vortex is in constant opposition to (and therefore represents
opposing pressure to) the weather patterns of the northern middle latitudes
opposing pressure to) the weather patterns of the northern middle latitudes
(i.e. Northern Europe, Northern Asia and northern North America).
(i.e. Northern Europe, Northern Asia and northern North America).
AO measures the variation in the strength, intensity and size of the jet
AO measures the variation in the strength, intensity and size of the jet
stream as it expands and contracts to alter the shape of the fast-flowing
stream as it expands and contracts to alter the shape of the fast-flowing
air current. AO is measured by opposing sea-pressure anomalies, ranging
air current. AO is measured by opposing sea-pressure
anomalies, ranging
th
from the Arctic Circle approximately to the 38 thparallel.
from the Arctic Circle approximately to the 38 parallel.
The Arctic Oscillation helps define the
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
jet stream, which can send cold, polar
air far south with its large oscillations.
air far south with its large oscillations.
This image compares December 2010
This image compares December 2010
to the previous 10-year average,
to the previous 10-year average,
showing that AO and the shape of the
showing that AO and the shape of the
jet stream altered the temperature
jet stream altered the temperature
gradient in the Northern Hemisphere.
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
indicates areas that are warmer
(colder) than average. Note how the jet
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
stream’s strange shape can juxtapose
warm and cold weather anomalies,
warm and cold weather anomalies,
with less than 50 miles between
with less than 50 miles between
extended warm and cold fronts.
extended warm and cold fronts.
During the ‘negative phase’ of AO, sea-level pressure is high in the
During the ‘negative phase’ of AO, sea-level pressure is high in the
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
AO has the exact opposite pattern.
AO has the exact opposite pattern.
Dr. James E. Hansen of NASA describes AO thus:
Dr. James E. Hansen of NASA describes AO thus:
"The degree to which Arctic air penetrates into middle latitudes is related to
"The degree to which Arctic air penetrates into middle latitudes is related to
the AO index, which is defined by surface atmospheric pressure patterns.
the AO index, which is defined by surface atmospheric pressure patterns.
When the AO index is positive, surface pressure is low in the polar region.
When the AO index is positive, surface pressure is low in the polar region.
This helps the middle latitude jet stream to blow strongly and consistently
This helps the middle latitude jet stream to blow strongly and consistently
from west to east, thus keeping cold Arctic air locked in the polar region.
from west to east, thus keeping cold Arctic air locked in the polar region.
When the AO index is negative, there tends to be high pressure in the polar
When the AO index is negative, there tends to be high pressure in the polar
region, weaker zonal winds, and greater movement of frigid polar air into
region, weaker zonal winds, and greater movement of frigid polar air into
middle latitudes."
middle latitudes."
AO has a dominant role in determining the shape of the jet stream, which in
AO has a dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
phases, the jet stream tends to be reinforced and prevented from
shifting. This is an effect called eddy feedback.
shifting. This is an effect called eddy feedback.
By maintaining the shape and consistency of the jet stream, eddy feedback
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
not persist on a yearly basis.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
4 4 4
The
Science
of European
AO’s
Effects
on Northern
LatitudesExtratropical
Cyclones
During the positive phase, a strong Polar Vortex confines cold Arctic air
across
Polar Regions. Arctic air is kept in the north, resulting in brisk
Climatology
winters for Greenland, northern Scandinavia and Russia, but keeping
most
of Europe
and the
mainland
US relatively
warm.
The
major factors
driving
European
ETCs are
the Arctic Oscillation and
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
Extratropical storms are flung further north. AO positive creates
stormy
weather
in the UK and
Scandinavia, while Southwest Europe
Arctic
Oscillation
(AO)
and Mediterranean countries remain dry.
The Arctic is home to a semi-permanent low pressure circulation
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
of 2014. The Vortex is in constant opposition to (and therefore represents
opposing pressure to) the weather patterns of the northern middle latitudes
(i.e. Northern Europe, Northern Asia and northern North America).
Storms are pushed further
north and affect the UK and
Scandinavia.
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
Storms migrate further south
and affect southern Europe
and the Mediterranean.
AO measures the variation in the strength, intensity and size of the jet
stream as it expands and contracts to alter the shape of the fast-flowing
air current. AO is measured by opposing sea-pressure anomalies, ranging
th
from the Arctic Circle approximately to the 38 parallel.
During the ‘negative phase’ of AO, sea-level pressure is high in the
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
AO has the exact opposite pattern.
Dr. James E. Hansen of NASA describes AO thus:
Figure 2. Positive phase of Arctic Oscillation.
"The degree to which Arctic air penetrates into middle latitudes is related to
the the
AO negative
index, which
is defined
by surface
atmospheric
pressure
patterns.
During
phase,
the Polar
Vortex is
weakened by
influxes
of
When
the AO
indexCold
is positive,
surfacesouth
pressure
lowmeandering
in the polar region.
warm
air from
Siberia.
air migrates
withisthe
jet
This helps
latitude
stream
to blowEurope
stronglyand
andNorth
consistently
stream.
Arcticthe
airmiddle
masses
freezejetover
Northern
from west
to the
east,Mediterranean
thus keeping cold
air locked
the polar region.
America,
while
andArctic
Southwest
US in
experience
When winters.
the AO index is negative, there tends to be high pressure in the polar
stormier
region, weaker zonal winds, and greater movement of frigid polar air into
middle latitudes."
AO has a dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
shifting. This is an effect called eddy feedback.
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
Figure 3. Negative phase of Arctic Oscillation.
European Extratropical Cyclones | TransRe White Paper
!
European Extratropical Cyclones | TransRe White Paper
'!
4 5
The Science
of European
North
Atlantic Oscillation
(NAO)
Cyclones
Extratropical
Similar to AO, NAO is comprised of north-south dipole anomalies, but
is
centered over the North Atlantic Gyre. The low pressure center is
Climatology
located over Stykkisholmur/Reykjavík Iceland, while the high pressure
anomaly
is factors
centered
over the
Ponta Delgada,
The major
driving
European
ETCs areAzores.
the Arctic Oscillation and
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air
farfigure
southfrom
with Willis
its large
The
Re oscillations.
shows the
This
image
compares
December
2010
effect of positive and negative NAO
to
the
previous
10-year
average,
phases on European windstorm
showing
that AOstrong
and the
shape on
of the
losses. NAO’s
influence
the
jet
stream
altered
the
temperature
path of ETCs has a significant effect
gradient
in the Northern
Hemisphere.
on loss structure
and distribution
in
Arctic
air
was
sent
as
far
south
as
Europe, with a 10-15% increase the
Carolinas
and
Portugal. Red
(blue)
(decrease)
in aggregate
losses
during
indicates
areas
that
are
warmer
NAO positive (negative) seasons.
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
It is important to note that the centers of the low and high pressure systems
migrate
a seasonal and(AO)
yearly basis; other locations can also be used to
ArcticonOscillation
measure the NAO index.
The Arctic is home to a semi-permanent low pressure circulation
Both
phases
NAO Vortex’,
are associated
withtolarge-scale
in
known
as theof‘Polar
which rose
prominencealterations
in the first quarter
strength
and
location
of
the
North
Atlantic
jet
stream
and
subsequent
of 2014. The Vortex is in constant opposition to (and therefore represents
storm
tracks.
Theyto)
also
modulate
patterns
heat andmiddle
moisture
opposing
pressure
theboth
weather
patterns
of theofnorthern
latitudes
transportation,
which affect
spatial
temperature
andNorth
precipitation
patterns
(i.e. Northern Europe,
Northern
Asia
and northern
America).
from the Eastern Europe to the coast of North America.
AO measures the variation in the strength, intensity and size of the jet
Typically,
affectsand
weather
patterns
across
Northern
Europe,
stream asNAO
it expands
contracts
to alter
the shape
of the
fast-flowing
Greenland,
Iceland
and Eastern
US/Canada.
It also has
the capability
to
air current. AO
is measured
by opposing
sea-pressure
anomalies,
ranging
th Europe over the summer
extend
into
Scandinavia
in winter andtoSouthern
from the
Arctic
Circle approximately
the 38 parallel.
months.
During the ‘negative phase’ of AO, sea-level pressure is high in the
During
of eithermiddle
positive
or negative
anomalous
Arctic prolonged
and low inperiods
the northern
latitudes.
TheNAO,
‘positive
phase’ of
weather
can opposite
be seen as
far east as central Russia and north Siberia.
AO has bands
the exact
pattern.
NAO
exhibits
a seasonal
andAO
yearly
basis, with prolonged
Dr. James
E. variability
Hansen ofonNASA
describes
thus:
periods of either phase dominating Atlantic weather patterns. From 1954"The degree
to which
air penetrates
middle latitudes
is related
1978,
a negative
NAOArctic
dominated
Atlanticinto
circulation
patterns
for overto
the AO
index,
which is defined by surface atmospheric pressure patterns.
75%
of the
time.
When the AO index is positive, surface pressure is low in the polar region.
During
the 24-year
period,
the jet
negative
dominated
at consistently
least three
This helps
the middle
latitude
streamNAO
to blow
stronglyfor
and
years
straight,
with thus
little keeping
to no presence
of a air
positive
from west
to east,
cold Arctic
lockedphase.
in the NAO
polar positive
region. did
not
appear
as
a
seasonal
mean
in
consecutive
years.
When the AO index is negative, there tends to be high pressure in the polar
region, weaker zonal winds, and greater movement of frigid polar air into
The winter of 2013-14 has had an overwhelmingly positive NAO index.
middle latitudes."
This provided more energy in the North Atlantic for intense and
clustered
storms, which
explain the
Storm
Series
(November
AO has a dominant
role inhelps
determining
the Nordic
shape of
the jet
stream,
which in
th
th
13
December
19role
, 2013)
and the
almost continuous
series
of storms
turnto
plays
a crucial
in steering
European
ETCs. During
active
ETC
th
th
from
December
, 2013
through
February
20 , and
2014prevented
across Europe.
phases,
the jet17
stream
tends
to be
reinforced
from
shifting. This is an effect called eddy feedback.
Though they are two different climate indices, NAO and AO ultimately
measure
the same
phenomenon.
They both
calculate
large-scale
By maintaining
the shape
and consistency
of the
jet stream,
eddy feedback
differences
pressure
in the Northern
Hemisphere,
and the
increases in
thesea-level
propensity
for clustering
of ETCs.
Such clustering
ramifications
forseen
temperature
and storm
tracks
between
Europe
patterns were
during gradients
the destructive
1987,
1990,
2000 and
2014
and
North
America.
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
4 6 6
The Science of European Extratropical
Cyclones
Positive NAO
When NAO is in its positive phase, the Icelandic low and Azores high are
Climatology
strengthened.
Heightened pressure systems lead to an increased pressure
gradient across the North Atlantic Gyre. Because large barometric
The major factors driving European ETCs are the Arctic Oscillation and
differentials increase wind speeds between areas of high and low pressure,
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
Westerly winds intensify across the North Atlantic. This has the overall
Arctic
Oscillation
(AO)into Europe.
effect
of heavy
winds flowing
Just like a positive AO,
positive NAO sends intense
storms in to North Europe
and UK.
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended
warm andNAO
coldkeeps
fronts. the
The negative
UK and North Europe dry and
sends storms in to the
Mediterranean region.
The Arctic is home to a semi-permanent low pressure circulation
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
of 2014. The Vortex is in constant opposition to (and therefore represents
opposing pressure to) the weather patterns of the northern middle latitudes
(i.e. Northern Europe, Northern Asia and northern North America).
AO measures the variation in the strength, intensity and size of the jet
stream as it expands and contracts to alter the shape of the fast-flowing
air current. AO is measured by opposing sea-pressure anomalies, ranging
th
from the Arctic Circle approximately to the 38 parallel.
During the ‘negative phase’ of AO, sea-level pressure is high in the
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
AO has the exact opposite pattern.
Dr. James E. Hansen
NASA phase
describes
AO Atlantic
thus: Oscillation.
Figure 4.ofPositive
of North
"The degree NAO
to which Arctic air penetrates into middle latitudes is related to
Negative
the AO index, which is defined by surface atmospheric pressure patterns.
When theNAO
AO index
positive,
surface
pressureNAO.
is lowIninthe
thenegative
polar region.
Negative
is the is
exact
opposite
of positive
phase,
This
helps thebetween
middle latitude
jet stream
to blow
strongly
consistently
the
difference
the Azores
high and
Icelandic
lowand
lessens,
from west tothe
east,
thus
keepinggradient.
cold ArcticThe
air locked
in the
polar region.
decreasing
sea
pressure
slackened
gradient
results in
When the
AO index and
is negative,
there
to be high pressure in the polar
weaker
Westerlies
less wind
in tends
Europe.
region, weaker zonal winds, and greater movement of frigid polar air into
middle latitudes."
AO has a dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
shifting. This is an effect called eddy feedback.
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
Figure 5. Negative phase of North Atlantic Oscillation.
4 European Extratropical Cyclones | TransRe White Paper
7 European Extratropical Cyclones | TransRe White Paper
7
The Science
of European
Extratropical
Relationship
between
Madden-Julian
Oscillation
(MJO)
and
NAO/AO
Cyclones
A
2008 study by Hai Lin, Gilbert Brunet and Jacques Derome of
Climatology
Environment Canada and McGill University found an observed connection
between
NAOdriving
and Madden-Julian
Oscillation
(MJO).
The majorthe
factors
European ETCs
are the Arctic
Oscillation and
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
airMJO
far south
with its large atmospheric
oscillations.
is a slow-moving
This
image
compares
December
2010
pattern that impacts global tropical
to and
the previous
10-year
average,
sub-tropical weather. It can be
showing
AO and
the shape
of the
trackedthat
through
NOAA’s
dynamic
jetMJO
stream
altered
the
temperature
forecast.
gradient in the Northern Hemisphere.
Above,
the forecast
index
is divided
Arctic
air was
sent as far
south
as the
into octants,
with eachRed
eighth
of the
Carolinas
and Portugal.
(blue)
index corresponding
a different
indicates
areas that areto
warmer
globalthan
tropical
basin.Note how the jet
(colder)
average.
stream’s strange shape can juxtapose
When
index
is within
the center
warm
andthe
cold
weather
anomalies,
circle,
MJO
is
considered
weak and
with less than 50 miles between
difficult warm
to read.
MJO
extended
and
coldbecomes
fronts.
stronger as the index moves further
from the center.
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
MJO is a band of low-pressure that develops in the Indian Ocean before
propagating
east as an anomalous
Arctic Oscillation
(AO) and convective weather band. It dumps
rain on Southeast Asia and Australia, continues east towards the Pacific,
The ultimately
Arctic is home
tothe
a semi-permanent
low pressure
circulation
and
impacts
Atlantic Ocean before
dissipating
near Africa.
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
MJO
is associated
large-scale
variations
in atmospheric/oceanic
of 2014.
The Vortex with
is in constant
opposition
to (and
therefore represents
indices,
affecting
drought,
monsoon
and
tropical
in every
opposing pressure to) the weather patterns of thecyclone
northernpatterns
middle latitudes
ocean
basin. MJO
canNorthern
also affect
through North
a complex
interaction
(i.e. Northern
Europe,
AsiaETCs
and northern
America).
with NAO and AO.
AO measures the variation in the strength, intensity and size of the jet
The
authors
the 2008and
study
found a to
long-distance
connection
between
stream
as it of
expands
contracts
alter the shape
of the fast-flowing
tropical
convection
of MJO and
the Northern
Hemisphere’s
NAO. When
air current.
AO is measured
by opposing
sea-pressure
anomalies,
ranging
th positive amplification
MJO
is inArctic
Phases
2-4,
NAO has a significant
from the
Circle
approximately
to the 38 parallel.
about 5-15 days after depressed convection of MJO reaches the
During the
‘negative
phase’ of AO, sea-level pressure is high in the
tropical
central
Pacific.
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
Conversely,
is in pattern.
Phases 6-8, there is a significant negative
AO has the when
exact MJO
opposite
amplification roughly 5-15 days after enhanced convection of MJO
Dr. James
E.tropical
Hansen central
of NASAPacific.
describes AO thus:
reaches
the
"The degree
air penetrates
into
middle
latitudes
MJO
also hastoawhich
strongArctic
relationship
with AO.
When
MJO
relatedis related to
the AO index,
is defined
by surface
atmospheric
convection
iswhich
enhanced
(depressed)
over
the Indianpressure
Ocean, patterns.
AO tends
When
theits
AO
index is(negative)
positive, surface
to
favor
positive
phase.pressure is low in the polar region.
This helps the middle latitude jet stream to blow strongly and consistently
As
NAO
AO are
intrinsically
related,
weair
see
how in
thethe
tropical
from
westand
to east,
thus
keeping cold
Arctic
locked
polar MJO
region.
influences
North
Atlantic
winter
weather.
The
results
indicate
that
When the AO index is negative, there tends to be high pressure inMJO
the polar
forces
a direct
influence
the Atlantic
sector’s
NAO
and
region, have
weaker
zonal winds,
and on
greater
movement
of frigid
polar
air AO.
into
middle latitudes."
An additional strong connection has been observed between MJO and
the
Northern
Hemisphere’s
winter stratospheric
AO has
a dominant
role in determining
the shape of Polar
the jetVortex.
stream,Large
which in
variations
in
the
jet
stream
and
sudden
warming
events
tend toETC
follow
turn plays a crucial role in steering European ETCs. During active
certain
phases.
This
provides
for support
for the complex
phases,MJO
the jet
stream
tends
to be further
reinforced
and prevented
from and
important
link between
global
tropical
weather
and North Atlantic winter
shifting. This
is an effect
called
eddy
feedback.
storms.
By maintaining the shape and consistency of the jet stream, eddy feedback
Due
to the observed
relationships
betweenofMJO
convection
and NAO/AO
increases
the propensity
for clustering
ETCs.
Such clustering
behavior,
thereseen
exists
the potential
to create1987,
medium
longand
range
patterns were
during
the destructive
1990,to2000
2014
forecasts
for
NAO
and
AO,
given
accurate
predictions
of
MJO
phase
European ETC seasons. This is a month-to-month phenomenon. It does
and
future on
movements.
not persist
a yearly basis.
A predictive method of this sort would allow for more detailed and farsighted forecasts for ETCs.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
4 8 8
The Science of European Extratropical
Characteristics
of Extratropical Cyclones
Cyclones
Characteristics
of
Cyclones
Characteristics
of Extratropical
Extratropical Cyclones
Dynamics
Dynamics
Climatology
Dynamics
We can see the importance of
We can
can see
see the
the importance
importance of
of
We
an in-depth
knowledge
of the
an
in-depth
knowledge
of
the
an
in-depth
of the
the
science
andknowledge
workings of
science
and
workings
of
the
science
and
workings
of
the
NAO and AO indexes, which
NAO
and AO
indexes,
which
NAO
indexes,
which and
track and
that AO
exact
temperature
track that
that exact
exact temperature
temperature and
and
track
pressure gradient, as well as the
pressure
gradient,
as
well
as
the
pressure
gradient,
the
shape and
locationasofwell
the as
North
shape
and
location
of
the
North
shape
and
location
of
the
North
Atlantic jet stream.
Atlantic
Atlantic jet
jet stream.
stream.
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
Phase
I- A altered
perturbation
forms
jet stream
the temperature
Phase
I- A
forms
Phase
Ainperturbation
perturbation
along
aI- baroclinic
zone forms
between
gradient
the
Northern
Hemisphere.
along a
a baroclinic
baroclinic zone
zone between
between
along
low
and
high
pressure
systems.
Arctic air
was sent as systems.
far south as the
low
low and
and high
high pressure
pressure systems.
Carolinas and Portugal. Red (blue)
Phase II- The wave amplifies,
indicates
areas
thatamplifies,
are warmer
Phase
IIwave
Phase
II- The
The
wave
scale contracts
and amplifies,
the fronts of
(colder)
than
average.
scale contracts
contracts and the Note
frontshow
of the jet
scale
the storm form.and the fronts of
the
storm
form.
stream’s
the
storm strange
form. shape can juxtapose
warm
and
coldfronts
weather
anomalies,
Phase III-The
‘T-bone’
and
Phase
III-The
fronts
‘T-bone’
and
Phase
III-The
fronts
‘T-bone’
and
with
less
than
50
miles
between
waves amplify. Storm force winds
waves
amplify.
Storm
forcefronts.
winds
waves
amplify.
Storm
force
extended
warm
and
cold
form
between
the
warm
andwinds
form
between
the
warm
and
form
between
the warm and
occluded
fronts.
occluded
occluded fronts.
fronts.
Phase IV-Full seclusion of the
Phase IV-Full
IV-Full seclusion
seclusion of
of the
the
Phase
warm front. Storm
and hurricane
warm
front.
Storm
and
hurricane
warm
hurricane
force front.
windsStorm
found and
on cold
side of
force
winds
found
on
cold
side
of
force
winds
found
on
cold
side
of
the occluded front.
the
occluded
front.
the occluded front.
Every year, approximately 200 extratropical disturbances form in the North
Every
approximately
200
extratropical
disturbances
form
in
Theyear,
major
factors
European
ETCs
are
the Arctic
Oscillation
and
Every
year,
approximately
extratropical
form
in the
the North
North
Atlantic.
They
derivedriving
their200
energy
from
thedisturbances
horizontal
temperature
Atlantic.
They
derive
their
energy
from
the
horizontal
temperature
North
Atlantic
Oscillation,
two
climate
indices
for
the
Northern
Hemisphere.
Atlantic.
They
derive
their
energy
from
the
horizontal
temperature
differential between warm, subtropical air masses and cold, Arctic air
differential between
between warm, subtropical
subtropical air masses
masses and
and cold,
cold, Arctic
Arctic air
air
differential
masses. Most stormswarm,
develop during the air
winter months,
when the
Arctic
Oscillation
(AO)
masses.
Most
storms
develop
during
the
winter
months,
when
the
masses.
Mostdifferential
storms develop
during
the winter
when
the
temperature
between
the tropics
andmonths,
poles are
the greatest.
temperature
temperature differential
differential between
between the
the tropics
tropics and
and poles
poles are
are the
the greatest.
greatest.
The Arctic is home to a semi-permanent low pressure circulation
Cold core disturbances that organize into larger storms and track east
known
the ‘Polar Vortex’,
which rose
prominence
thetrack
first quarter
Cold
core as
disturbances
that organize
organize
into to
larger
storms in
and
track
east
Cold
core
disturbances
that
larger
storms
and
are steered
by the jet stream.
With its into
undulating
movements
and east
of
2014.
The
Vortex
is
in
constant
opposition
to
(and
therefore
represents
are
steered
by
the
jet
stream.
With
its
undulating
movements
and
are
steered erratic
by theoscillations,
jet stream. the
With
undulating
movements
andstorm
sometimes
jetitsstream’s
shape
helps define
opposingerratic
pressure
to) the weather
patterns of
the northern
middle
latitudes
sometimes
oscillations,
the
jet
stream’s
shape
helps
define
storm
sometimes
erratic
oscillations,
the
jet
stream’s
shape
helps
define
track. Because the AO and NAO help define the extremes of the storm
(i.e.
Northern
Europe,
Northern
Asia
and
northern
North
America).
track.
Because
the
AO
and
NAO
help
define
the
extremes
of
the
track.
Becauseinthe
NAOa help
define
the extremes
eccentricities
theAO
jet and
stream,
refined
understanding
of of
thethe
development
eccentricities in
in the
the jet
jet stream,
stream, a
a refined
refined understanding
understanding of
of the
the development
development
eccentricities
of AO
AO/NAO
is
imperative
to
understand
both
past
and
future
trends.
measures
the variation
in the strength,
intensity
and size of the jet
of
of AO/NAO
AO/NAO is
is imperative
imperative to
to understand
understand both
both past
past and
and future
future trends.
trends.
stream as it expands and contracts to alter the shape of the fast-flowing
Storms that affect Europe have tracked across the North Atlantic with the
air current.
AO is
measured
opposing
sea-pressure
anomalies,
Storms
that
affect
Europe
have
tracked
across
the North
with
the
Storms
that upper-atmospheric
affect
Europe
haveby
tracked
across
North Atlantic
Atlantic
with ranging
the
sinusoidal,
jet
stream.
Withthe
an
th average forward motion of
from
the
Arctic
Circle
approximately
to
the
38
parallel.
sinusoidal, upper-atmospheric
upper-atmospheric jet
jet stream.
stream. With
With an
an average
average forward
forward motion
motion of
of
sinusoidal,
35mph, an ETC’s asymmetrical windfield creates the greatest swath of
35mph,
an
ETC’s
asymmetrical
windfield
creates
the
greatest
swath
of
35mph,
an ETC’s
windfield
creates
the greatest
swath of
damage
itsasymmetrical
southeast
quadrant
near
the pressure
frontal
wave.
Duringalong
the ‘negative
phase’
of AO, sea-level
is high in the
damage
damage along
along its
its southeast
southeast quadrant
quadrant near
near the
the frontal
frontal wave.
wave.
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
European ETCs can, at times, produce gusts in excess of 150 mph.
AO has ETCs
the exact
European
ETCs
can,opposite
at times,
times, pattern.
produce gusts
gusts in
in excess
excess of
of 150
150 mph.
European
can,
at
produce
These storms,
(which
include) Xynthia
or Kyrill, experienced
rapid mph.
These
storms,
(which
include)
Xynthia
or
Kyrill,
experienced
rapid
These
storms, (which
include) Xynthia
or Kyrill,
experienced
intensification
after
interacting
withdescribes
a trough
of low
pressure rapid
high in the
Dr. James E.
Hansen
of NASA
AO
thus:
intensification
after
interacting
with
a
trough
of
low
pressure
high
in
intensification
after
interacting
with
a
trough
of
low
pressure
high
in the
the
atmosphere.
atmosphere.
atmosphere.
"The degree to which Arctic air penetrates into middle latitudes is related to
the AO index, which is defined by surface atmospheric pressure patterns.
When the AO index is positive, surface pressure is low in the polar region.
This helps the middle latitude jet stream to blow strongly and consistently
from west to east, thus keeping cold Arctic air locked in the polar region.
When the AO index is negative, there tends to be high pressure in the polar
region, weaker zonal winds, and greater movement of frigid polar air into
middle latitudes."
AO has a dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
shifting. This is an effect called eddy feedback.
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
Figure 6. The Shapiro-Keyser Extratropical Cyclone Model, developed in 1990 shows
Figure
6.
Shapiro-Keyser
Extratropical
Figure
6. The
Theof
Shapiro-Keyser
Extratropical Cyclone
Cyclone Model,
Model, developed
developed in
in 1990
1990 shows
shows
the life-cycle
an ETC.
the
life-cycle
of
an
ETC.
the life-cycle of an ETC.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
European
European Extratropical
Extratropical Cyclones
Cyclones || TransRe
TransRe White
White Paper
Paper
9 9 9 4 9
The Science
of European
Structure,
Shape and
Size
Cyclones
Extratropical
ETCs differ in structure, shape and size from Atlantic, east Pacific,
west
Pacific and Indian Ocean hurricanes/typhoons. The latter are warm
Climatology
core tropical cyclones, deriving their energy from a vertical temperature
differential
between
upper
and lower
atmosphere.
The major
factorsthe
driving
European
ETCs
are the Arctic Oscillation and
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
Because ETCs are fueled by a horizontal temperature differential, they do
notArctic
lose strength
as they track
over land, unlike tropical cyclones.
Oscillation
(AO)
ETCs keep their energy throughout landfall, affecting a single location
The Arctic
is home
to24
a semi-permanent
low pressure circulation
anywhere
between
6 and
hours.
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
Another
difference
between
ETCs and
tropicaltocyclones
is therepresents
distinct
of 2014.
The Vortex
is in constant
opposition
(and therefore
fronts.
The
comma-shaped
appearance
of
ETCs
identifies
the
location
opposing pressure to) the weather patterns of the northern middle latitudes
of warm
and cold
air masses
thatAsia
feed
thenorthern
circulation
ofAmerica).
the storm. The
(i.e. Northern
Europe,
Northern
and
North
distinct warm and cold fronts pack the greatest punch, with the highest
AO measures
variation
in the strength,
intensity
and size of the jet
surface
winds andthe
heaviest
precipitation
along their
boundaries.
stream as it expands and contracts to alter the shape of the fast-flowing
ETCs
become AO
asymmetric
when
because
the tropical
and polar
air
air current.
is measured
bymature
opposing
sea-pressure
anomalies,
ranging
th temperature and
masses
thatArctic
provide
the approximately
energy are not to
uniform
from the
Circle
the 38in parallel.
pressure. Full-blown storms vary greatly in size, with diameters ranging
During
the ‘negative
phase’
of of
AO,
sea-level
pressure
istends
high in
from
120-1200
miles. The
spread
most
damaging
winds
tothe
stay
Arctic
and
low
in
the
northern
middle
latitudes.
The
‘positive
phase’
of
within 50-150 miles of the storm center.
AO has the exact opposite pattern.
Dr. James E. Hansen of NASA describes AO thus:
"The degree to which Arctic air penetrates into middle latitudes is related to
the AO index, which is defined by surface atmospheric pressure patterns.
When the AO index is positive, surface pressure is low in the polar region.
This helps the middle latitude jet stream to blow strongly and consistently
from west to east, thus keeping cold Arctic air locked in the polar region.
When the AO index is negative, there tends to be high pressure in the polar
region, weaker zonal winds, and greater movement of frigid polar air into
middle latitudes."
AO has a dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
shifting. This is an effect called eddy feedback.
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
Figure
7. This shows
the windstorm
of Xynthia (Febphenomenon.
2010) on the left
European
ETC seasons.
Thisfootprints
is a month-to-month
It and
does
Kyrill
(Jan
2007)
on
the
right.
Although
each
storm
had
a
slightly
different
storm
track,
not persist on a yearly basis.
one can see how the storms did not lose energy over land and were able to maintain
strength deep into the European continent. Xynthia traveled over 1700 miles into
Europe, Kyrill covered over 1800 miles.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
10 4 10
!
!
Climate Indices Chosen:
AAO- Antarctic Oscillation
AO- Arctic Oscillation
Climate Indices Chosen:
AMM- Atlantic Meridianal Mode
AAO- Antarctic Oscillation
AMOAtlantic
Multi-Decadal Oscillation
AOArctic Oscillation
MEI-AMMMultivariate
Index
Atlantic ENSO
Meridianal
Mode
MJOMadden
Julian
Oscillation
AMOAtlantic
Multi-Decadal
Oscillation
MEIMultivariate
Index
NAONorth
Atlantic ENSO
Oscillation
Madden
Oscillation
ONI-MJOOceanic
NinoJulian
Index
NAO- North Atlantic Oscillation
PDO- Pacific Decadal Oscillation
ONI- Oceanic Nino Index
SOI- Southern Oscillation Index
PDO- Pacific Decadal Oscillation
QBO- Quasi-Biennial Oscillation
SOI- Southern Oscillation Index
!Climate
QBOQuasi-Biennial
Oscillation
Variables
Chosen:
The Arctic Oscillation helps define the
jet850mb
stream,
which
canAnomaly
send
cold, polar
!Climate
Zonal
Wind
Variables
Chosen:
air far south with its large oscillations.
300mb
Zonal
Wind
Anomaly
850mb
Zonal
Wind
Anomaly
This image
compares
December
2010
Zonal
Wind
Anomaly
Water
Anomaly
toPrecipitable
the 300mb
previous
10-year
average,
showing
that AO and
theAnomaly
shape of the
Precipitable
Water
Surface
Pressure
Anomaly
jet stream altered the temperature
Surface Pressure Anomaly
!
gradient
in the Northern Hemisphere.
Storms Chosen:
!
Arctic air was sent as far south as the
Storms Chosen:
1953 N Sea
JanRed
1953
Carolinas
andFloodPortugal.
(blue)
1953areas
N Seathat
Flood1953
indicates
are Jan
warmer
Capella (Jan 1976 Gale) - Jan 1976
(colder)
than average.
jet
Capella
(Jan 1976Note
Gale)how
- Janthe
1976
Great
Storm
of
’87Oct
1997
stream’s
strange
juxtapose
Great
Stormshape
of ’87- can
Oct 1997
warm
and
cold
weather
anomalies,
DariaDaria
(Burns’
Day Storm) - Jan 1990
(Burns’ Day Storm) - Jan 1990
with less than 50 miles between
VivianFeb
1990
VivianFeb
1990
extended
warm
and
cold fronts.
Wiebke-Feb
1990
Wiebke-Feb
1990
Lothar1990
LotharDecDec
1990
Anatol-Dec
1999
Anatol-Dec
1999
Martin- Dec 1999
Martin- Dec 1999
Kyrill- Jan 2007
Kyrill- Jan 2007
The
Science
of European Extratropical
Historical
Record
Cyclones
An inherent necessity of any Chief Risk Officer or Chief Catastrophe Officer
is the ability to minimize risk, maximize opportunity and maintain business
Climatology
continuity. Understanding loss history and large-scale climate indices plays
The
major factors
driving
European
are theofArctic
Oscillation
and
an important
role in
the analysis
andETCs
calculation
business
opportunities.
An inherent
necessity
of anytwo
Chief
Risk Officer
or Chief
Catastrophe
Officer
North
Atlantic
Oscillation,
climate
indices
for the
Northern Hemisphere.
Historical Record
is the ability to minimize
risk, maximize opportunity and maintain business
Accuweather
Study
continuity.Oscillation
Understanding loss
history and large-scale climate indices plays
Arctic
(AO)
anApril
important
role
in the
analysis and
of business
opportunities.
In
2014,
Dan
Kottlowski
of calculation
Accuweather
completed
a study on our
The
Arctic
is home
to adevelopment,
semi-permanent
low pressure
circulation
behalf
on the
genesis,
intensity,
track and
clustering of
Accuweather Study
known
as the
‘Polar
Vortex’,
which
roseindices
to prominence
in the first
European
ETCs
using
various
climate
and signals.
The quarter
study is
In2014.
April 2014,
Dan
Kottlowski
of Accuweather
completed
a study
on
our
of
The
Vortex
is in
constant
opposition
to (and
therefore
represents
intended
to show
how
readers
might
use climate
indices
and other
signals to
behalf on pressure
the
genesis,
intensity,oftrack
and clustering
opposing
to) development,
the weather
patterns
the northern
middleoflatitudes
anticipate
active
European
ETC seasons.
European
ETCs
using various
indices
and signals.
The study is
(i.e.
Northern
Europe,
Northernclimate
Asia and
northern
North America).
intended
to focused
show howon
readers
might use climate
indices
and other
signals
to
The
study
13 high-impact
storms
between
1953
and 2013.
anticipate
active
European
ETC
seasons.
AO
measures
variation
the strength,
and sizetoof
the jet
Various
climatethe
indices
(thoseinused
most oftenintensity
by Accuweather
assess
stream
as it expands
shape
of the
fast-flowing
storm.
Long
term
and short
foralter
eachthe
future weather
trends) and
werecontracts
evaluated to
The study focused on 13 high-impact storms between 1953 and 2013.
air
current.
AOwere
is measured
by
sea-pressure
ranging
indicesanomalies,
showed
little
Wopposing
term
trends
identified.
hile
some
ofbythe
Various
climate
indices
(those used
most
often
Accuweather
to assess
th
from
the
Arctic
Circle
approximately
to
the
38
parallel.
or
no predictive
skill, were
others
did.
future
weather trends)
evaluated
for each storm. Long term and short
term trends were identified. While some of the indices showed little
During
‘negative
phase’
oflisted
AO, that
sea-level
pressure
is high and
in the
Table
1.the
Seven
climate
indices
foretell active
ETC seasons
events.
or no predictive
skill, others
did.are
Arctic
low in
northern
middle
latitudes.
The ‘positive
Storms and
are listed
by the
insured
loss, indexed
to USD
2012. Insured
loss dataphase’
for the of
Table
1. Seven
climateopposite
indices
listed
that
active
events.
AO
has
the
exact
pattern.
1953
flood
is unavailable;
anare
estimate
wasforetell
provided
byETC
the seasons
UK Metand
Office
in a 60 year
Storms are listed by insured loss, indexed to USD 2012. Insured loss data for the
retrospective
study. The 1953 storm would have likely topped Daria in a modern
1953
flood isE.
unavailable;
providedAO
by the
UK Met Office in a 60 year
Dr.
James
Hansen an
ofestimate
NASA was
describes
thus:
climactic and economic scenario. ‘X’ means no data available, ‘POS’ means positive
retrospective study. The 1953 storm would have likely topped Daria in a modern
phase, ‘NEG’ means negative phase, ‘NEU’ means a Neutral ENSO, ‘LA’ means La
"The
degree
to which
Arctic ‘X’
airmeans
penetrates
into middle
latitudes
is related to
climactic
and economic
scenario.
no data available,
‘POS’
means positive
Nina,
‘EL
means
El negative
Nino, ‘MOD’
means
moderate
MJO,ENSO,
‘WK’ means
weakLaMJO,
phase,
‘NEG’
means
phase,
‘NEU’
means
a
Neutral
‘LA’
means
the AO index, which is defined by surface atmospheric pressure patterns.
‘STG’
means
strong
MJO.
! means moderate MJO, ‘WK’ means weak MJO,
Nina, ‘EL
El Nino,
When
themeans
AO index
is‘MOD’
positive,
surface pressure is low in the polar region.
‘STG’ means strong MJO.!
This helps the middle latitude jet stream to blow strongly and consistently
from west to east, thus keeping cold Arctic air locked in the polar region.
When the AO index is negative, there tends to be high pressure in the polar
region, weaker zonal winds, and greater movement of frigid polar air into
middle latitudes."
AO has a dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
shifting. This is an effect called eddy feedback.
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
Klaus- Jan 2009
Klaus- Jan 2009
Xynthia- Feb 2010
Xynthia- Feb 2010
St. Jude- Oct 2013
St. Jude- Oct 2013
!
!
!
European Extratropical Cyclones | TransRe White Paper
!
European
EuropeanExtratropical
ExtratropicalCyclones
Cyclones | | TransRe
TransReWhite
WhitePaper
Paper
##!
4 ##!
11
For storms with a west-southwest to east-northeast track, at least two
For
storms
west-southwest
to positive.
east-northeast
least two
of
the
QBO, with
NAOaand
AO indices are
Stormstrack,
with aatsouth-toofFor
thetrack
QBO,
NAO
and
AO
indices
are
positive.
Storms
with
a
south-tonorth
have
at
least
two
of
the
three
QBO,
NAO
and
AO
indices
storms with a west-southwest to east-northeast track, at least two
of the
QBO,
NAO
AO
indices
positive.
Storms
with
north
track
at and
least
two
of the are
three
QBO,
and
AOa south-toindicestrack.
negative.
A have
negative
AAO
correlates
closely
withNAO
the south-to-north
north
track
have at least
two
of the three
QBO,with
NAOthe
andsouth-to-north
AO indices track.
negative.
A negative
AAO
correlates
closely
Climatology
Annegative.
important
observation
the study
is the
of NAO
in the
A negative
AAOfrom
correlates
closely
withimportance
the south-to-north
track.
An The
important
observation
from
the
study
is
the
importance
of
NAO
in and
the
intensification
of
storm
development.
When
NAO
changes
sign
before
major factors driving European ETCs are the Arctic Oscillation
An
important
observation
from
the
study
is
the
importance
of
NAO
in
the
storm
NAO
changes
sign
before
aintensification
storm
usuallydevelopment.
from
to positive,
there
is potential
for
Northdevelops,
AtlanticofOscillation,
twonegative
climate When
indices
for the
Northern
Hemisphere.
intensification of storm development. When NAO changes sign before
a storm develops,
from negative
to positive,
thereanisincrease
potentialoffor
stronger
Europeanusually
ETC creation.
This finding
suggests
the
a Arctic
storm develops,
usually from
negative to positive, there is potential for
Oscillation
(AO)
stronger
European
ETC supports
creation.
This
finding
suggests antheory.
increase of the
jet
stream’s
power,
which
the
storm
intensification
stronger European ETC creation. This finding suggests an increase of the
jet stream’s power, which supports the storm intensification theory.
jetThe
stream’s
power,
which
the storm intensification
theory.
Arctic
is home
tosupports
a semi-permanent
low pressure
circulation
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
of 2014. The Vortex is in constant opposition to (and therefore represents
opposing pressure to) the weather patterns of the northern middle latitudes
(i.e. Northern Europe, Northern Asia and northern North America).
The Science of European Extratropical
Cyclones
AO measures the variation in the strength, intensity and size of the jet
stream as it expands and contracts to alter the shape of the fast-flowing
air current. AO is measured by opposing sea-pressure anomalies, ranging
th
from the Arctic Circle approximately to the 38 parallel.
During the ‘negative phase’ of AO, sea-level pressure is high in the
The Arctic Oscillation helps define the
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
AO has the exact opposite pattern.
jet stream, which can send cold, polar
air far south with its large oscillations.
Dr. James E. Hansen of NASA describes AO thus:
This image compares December 2010
to the previous 10-year average,
"The degree to which Arctic air penetrates into middle latitudes is related to
showing that AO and the shape of the
the AO index, which is defined by surface atmospheric pressure patterns.
jet stream altered the temperature
When the AO index is positive, surface pressure is low in the polar region.
gradient in the Northern Hemisphere.
This helps the middle latitude jet stream to blow strongly and consistently
Arctic air was sent as far south as the
from west to east, thus keeping cold Arctic air locked in the polar region.
Carolinas and Portugal. Red (blue)
When the AO index is negative, there tends to be high pressure in the polar
indicates areas that are warmer
region, weaker zonal winds, and greater movement of frigid polar air into
(colder) than average. Note how the jet
middle latitudes."
stream’s strange shape can juxtapose
AO has a dominant role in determining the shape of the jet stream, which in
warm and cold weather anomalies,
turn plays a crucial role in steering European ETCs. During active ETC
with less than 50 miles between
Figure 8. The various storm tracks of those listed in Table 1. The normal path of most
phases, the
jet stream
tends
to belisted
reinforced
and
from
extended warm and cold fronts.
Figure
storm tracks
those
in Table
Theprevented
normal
path
of most
storms8.isThe
fromvarious
the west-southwest
toofthe
east-northeast.
The 1.
remaining
storms
without
shifting.
is storm
an effect called
eddy
Figure
The This
various
those
listedfeedback.
inthe
Table
1. remaining
The normal
path of
most
storms
is8.from
the
west-southwest
toofthe
east-northeast.
The
without
the aforementioned
path taketracks
unusual
routes
through
North
Atlantic
andstorms
Europe.
storms
is from the west-southwest
to the
east-northeast.
remaining
storms
without
the
aforementioned
path take unusual
routes
through the The
North
Atlantic and
Europe.
By maintaining the shape and consistency of the jet stream, eddy feedback
Data
suggests that
with a general
the
aforementioned
pathfast
takemoving
unusualstorms
routes through
the Northwest-to-east
Atlantic and Europe.
increases
the
propensity
for
clustering
ofastream.
ETCs.
Such
clustering
orientation
track
with
strong
west-to-east
jet
A west-to-east
strong,
Data
suggests
that
fasta moving
storms
with
general
patterns
were
seen
during
the
destructive
1987,
1990,
2000
and 2014
horizontal
polar
jetwith
stream
positioned
acrosswith
North
the North
Data
suggests
that
fast
moving
storms
a America
general
west-to-east
orientation
track
a strong
west-to-east
jet
stream.and
A strong,
European
ETC
seasons.
This
isand
aacross
month-to-month
It does
Atlantic
ispolar
found
a positive
NAO
AO, and
favors
aphenomenon.
strong
midorientation
track
with
a strong
west-to-east
jet
stream.
Aand
strong,
horizontal
jetwith
stream
positioned
North
America
the North
not
persist
on
a
yearly
basis.
latitude
jet
stream,
fueling
development
of
strong
ETCs.
This
pattern
horizontal
polar jet
stream
positioned
across
America
and the
North
Atlantic
is found
with
a positive
NAO and
AO,North
and favors
a strong
midencourages
thewith
development
of
storm
clusters.
Atlantic
is found
a positive
NAO
andof
AO,
andETCs.
favorsThis
a strong
midlatitude
jet
stream,
fueling
development
strong
pattern
latitude jet stream,
fueling development
strong ETCs. This pattern
encourages
the development
of stormofclusters.
encourages the development of storm clusters.
12 European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
12 4 12 12
WhatisisQBO?
QBO?
What
The quasi-biennial oscillation (QBO)
The quasi-biennial oscillation (QBO)
is a slow moving pattern (average
is a slow moving pattern (average
cycle period is 28.5 months) of
cycle
period is waves.
28.5 months)
of
atmospheric
These waves
atmospheric
waves.troposphere
These waves
start in the tropical
and
start
in
the
tropical
troposphere
and
travel higher before being dissipated
travel
higher
before being
dissipated
in the
stratosphere,
and cause
successive
waves
of
easterly
in the stratosphere, and causeand
westerly wind
anomalies.
successive
waves
of easterly and
westerly wind anomalies.
The phases of QBO alter the strength
of the Atlantic jet stream: westerly
The phases of QBO alter the strength
(negative) phases weaken the
of the Atlantic jet stream: westerly
Atlantic jet stream, while easterly
(negative)
the
(positive)phases
phases weaken
strengthen
the jet
Atlantic
stream,
streamjetand
tend towhile
causeeasterly
stormier
(positive)
phases
strengthen the jet
European
winters.
stream
andOscillation
tend to cause
stormier
The Arctic
helps define
the
European
jet stream,winters.
which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
The Science of European Extratropical
The
positive
phase
of QBO
enhances
this jetthis
pattern
and aidsand
in the
The
positive
phase
of QBO
enhances
jet pattern
aids in the
Cyclones
development of ETC clustering with west-southwest to east-northeast
development of ETC clustering with west-southwest to east-northeast
tracks.
Climatology
tracks.
The more severe ETCs track through or near the English Channel, with
The
major
factors
driving
European
are the
and Channel, with
The
more
severe
ETCs
trackETCs
through
orArctic
nearOscillation
the English
a directional path towards the German Bight.
North
Atlantic Oscillation,
two climate
for the
Northern Hemisphere.
a directional
path towards
theindices
German
Bight.
Storms with southerly paths bring high impacts to South France and Spain,
while more northerly storms impact the UK. Areas east of the UK,
while
more
northerly
storms impact
the
Areascirculation
east
of Germany
the UK,
including
France,
the
Belgium,
Luxembourg
and
The
Arctic
is home
to aNetherlands,
semi-permanent
lowUK.
pressure
are
heavily
impacted
by
south-to-north
and west-southwest
toand Germany
including
France,
theboth
Netherlands,
Belgium,
Luxembourg
known
as the
‘Polar Vortex’,
which
rose to prominence
in the first quarter
east-northeast
storms.
are heavily
impacted
by both
south-to-north
and west-southwest
to
of 2014.
The Vortex
is in constant
opposition
to (and therefore
represents
Arctic
Oscillation (AO)
Storms with southerly paths bring high impacts to South France and Spain,
opposing
pressure to)
the weather patterns of the northern middle latitudes
east-northeast
storms.
However, there does not seem to be an efficient long-term predictor for
(i.e. Northern Europe, Northern Asia and northern North America).
the strength and path of storms. This is not very surprising, as highlyHowever, there does not seem to be an efficient long-term predictor for
funded
research
forecasting
storm intensification
AO
measures
theinvariation
in tropical
the strength,
intensity and shows
size ofonly
the jet
the strength and path of storms. This is not very surprising, as highly-
modestas
improvements.
Predicting
the to
path
and
ofthe
non-tropical
stream
it expands and
contracts
alter
thestrength
shape of
fast-flowing
funded
research
in
forecasting tropical storm intensification shows only
storms
is even
difficult.
air
current.
AO ismore
measured
by opposing sea-pressure anomalies, ranging
th
modest
improvements.
Predicting
and strength of non-tropical
from
the Arctic
Circle approximately
to thethe
38path
parallel.
With
potential
impacts
from
the
UK
into
Scandinavia,
storms with weststorms is even more difficult.
southwest
to east-northeast
can
track farisinto
During
the ‘negative
phase’ oforientations
AO, sea-level
pressure
highEurope.
in the
While
long-term
climate
signal
can
predict
paths,
a negative
and
Withno
potential
impacts
from
the
UK into
Scandinavia,
storms
Arctic
and
low in the
northern
middle
latitudes.
The
‘positive NAO
phase’
of with westnegative
AO
strongly
suggests
a
more
southerly
storm
track,
AO
has
the
exact
opposite
pattern.
southwest to east-northeast orientations can track far into Europe.
influencing
ETCs to impact
France
Spain,
with
possible
tracks into
While no long-term
climate
signaland
can
predict
paths,
a negative
NAO and
Dr.
James
E. Hansen
of NASA
describes AO
thus:
Italy
and Eastern
Europe.
Nevertheless,
these
climate signs can also
negative AO strongly suggests a more southerly storm track,
support storms that impact much larger areas if they track south-to-north, as
"The
degree to which
Arctic
air penetrates
into
middle
latitudes
related totracks into
influencing
ETCs
to impact
France
and
Spain,
with is
possible
with the case of the 1987 storm.
theItaly
AO index,
which is defined
by Nevertheless,
surface atmospheric
and Eastern
Europe.
thesepressure
climatepatterns.
signs can also
When
the
AO
index
is
positive,
surface
pressure
is
low
in
the
polar
support storms
thatthe
impact
much larger
areasgives
if they
trackregion.
south-to-north,
as
Reanalysis
data from
NCEP/NCAR
database
evidence
that a
This
helps
the
middle
latitude
jet
stream
to
blow
strongly
and
consistently
strong
jet
stream
with
anomalously
strong
winds
correlates
with
the
with the case of the 1987 storm.
from west to east, thus keeping cold Arctic air locked in the polar region.
development of stronger and more frequent high impact storms.
When
the AO index
is from
negative,
tends to bedatabase
high pressure
in the
polar
Reanalysis
data
thethere
NCEP/NCAR
gives
evidence
that a
region,
weakeryears
zonal with
winds,
and greater movement
of frigidofpolar
air into
Specifically,
a higher-than-normal
number
storms
strong jet stream with anomalously strong winds correlates with the
middle
latitudes."
clustered
together shows anomalously powerful wind flow at the
development of stronger and more frequent high impact storms.
300mb level. The 1999-2000 and 2013-2014 European ETC seasons are
AO has a dominant role in determining the shape of the jet stream, which in
particularly
good examples,
asashown
in Figure 9.
Specifically,
higher-than-normal
number
storms
turn
plays a crucialyears
role inwith
steering
European ETCs. During
active of
ETC
clustered
together
shows
anomalously
powerful
wind
flow at the
phases,
the jet
stream tends
to be
reinforced and
prevented
from
shifting.
This
is
an
effect
called
eddy
feedback.
300mb level. The 1999-2000 and 2013-2014 European ETC seasons are
particularly good examples, as shown in Figure 9.
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
4 European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
13
13 The Science of European Extratropical
Cyclones
Climatology
The major factors driving European ETCs are the Arctic Oscillation and
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
Arctic Oscillation (AO)
The Arctic is home to a semi-permanent low pressure circulation
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
of 2014. The Vortex is in constant opposition to (and therefore represents
opposing pressure to) the weather patterns of the northern middle latitudes
(i.e. Northern Europe, Northern Asia and northern North America).
AO measures the variation in the strength, intensity and size of the jet
stream as it expands and contracts to alter the shape of the fast-flowing
Figure 9. The NCEP/NCAR reanalysis of 300mb zonal wind in meters per second. On
Figure
9. The NCEP/NCAR
reanalysis
of
300mb zonal
wind in meters
per second.
On
AO isseason,
measured
opposing
sea-pressure
anomalies,
ranging
the leftair
is current.
the 1999-2000
on thebyright
is the 2013-2014
season.
For the 1999th
the
left
is9.the
1999-2000
season,
on the of
right
is the
2013-2014
For second.
the 1999Figure
The
NCEP/NCAR
reanalysis
300mb
wind
inseason.
meters per
On
from
the
Arctic
Circle
approximately
thezonal
38degrees
parallel.
2000 season,
the
anomalous
wind
band extendstoover
70
longitude.
2000
season,
anomalous
windon
band
over
70 degrees
longitude.
the left
is the the
1999-2000
season,
the extends
right is the
2013-2014
season.
For the 1999-
During
the
phase’
of AO,
sea-level
is
high in the
season,
the‘negative
anomalous
wind band
extends
over
70 pressure
degrees
longitude.
In 2000
both
scenarios,
surface
storms
tend
to form
in the
left front
quadrant
In both
scenarios,
surface
storms
tend
to form
inanomaly.
theThe
left ‘positive
front
quadrant
and
the
right
rear
quadrant
of the oval
shaped
wind
This means
Arctic
and
low
in the northern
middle
latitudes.
phase’ of
and
theseparate
right
rear
quadrant
of the
shaped
wind
anomaly.
This
means
In two
both
scenarios,
surface
tend
to form
in the
leftwithin
front
quadrant
that
storms
canstorms
form
atoval
nearly
the same
time
this
AO
has
the
exact
opposite
pattern.
that
two
at nearly
the
same
timeEurope,
within
this
andlevel
the separate
right
rearstorms
quadrant
ofform
the oval
shaped
wind
anomaly.
This means
high
wind flow
patterncan
and
maintain
parallel
tracks
into
E.
Hansen
ofcan
NASA
describes
AOthe
thus:
high
level
wind
flow
pattern
and
maintain
parallel
tracks
into
Europe,
thatDr.
two
separate
storms
form
at nearly
same
time
within
this
creating
aJames
storm
family
or
storm
cluster.
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
creating
a storm
or stormand
cluster.
high level
windfamily
flow pattern
maintain parallel tracks into Europe,
th
to the previous 10-year average,
A good
example
‘clustered
struck into
Europe
overlatitudes
Februaryis10
"The
degreeoftothese
which
Arctic airETCs’
penetrates
middle
related
to
creating
a
storm
family
or
storm
cluster.
th
showing that AO and the shape of the 14A good
th
of
2014.
Figure
1
(inside
front
page)
shows
how
some
patterns
the AO
index,ofwhich
defined by
surface
atmospheric
pressure
patterns.
example
theseis‘clustered
ETCs’
struck
Europe over
February
10 jet stream altered the temperature
th
th
combined
and
intensified
storms.
When
theFigure
AO
index
is into
positive,
pressure
is low
in the
polar region.
14
A good
example
of
these
‘clustered
ETCs’ shows
struck Europe
over
February
10 of 2014.
1 (inside
frontsurface
page)
how
some
patterns
th
gradient in the Northern Hemisphere. combined
helps
the
middle
latitude
jet stream
to blowhow
strongly
and
consistently
and
intensified
intofront
storms.
14 This
of 2014.
Figure
1 (inside
page) shows
some
patterns
cover image of this paper shows waves striking a lighthouse and a
Arctic air was sent as far south as the The
th region.
from
west
to
east,
thus
keeping
cold
Arctic
air
locked
in
the
polar
combined
intensified
into storms.
pier
at Douro’sand
river
mouth in Porto,
Portugal on Monday, February 10 ,
Carolinas and Portugal. Red (blue)
TheWhen
coverthe
image
of
this
paper
shows
waves
striking
a
lighthouse
and a
AO index
is negative,
high pressure
2014. This particular
cluster
put the there
entiretends
coasttoofbe
Portugal
on the in ththe polar
pier
atcover
Douro’s
river
mouth
in
Porto,
Portugal
on
Monday,
February
Theregion,
image
of
this
paper
shows
waves
striking
a
lighthouse
and
a
indicates areas that are warmer
weaker
zonal
winds,Stephanie
and greater
movement
of frigid polar10
air, into
highest scale
of alert
as storm
rolled
in.
th
piermiddle
atThis
Douro’s
river
mouth
in
Porto,
Portugal
on
Monday,
February
10
,
particular
cluster
put
the
entire
coast
of
Portugal
on
the
(colder) than average. Note how the jet 2014.
latitudes."
highest
scale
of
alert
as
storm
Stephanie
rolled
in.
2014.
This
particular
cluster
put
the entire
coast
of Portugal
on in
the
300mb
high
level
winds
can be
predicted
with
a certain
level of skill
stream’s strange shape can juxtapose The
AOclimate
has
a model
dominant
role
inThe
determining
shape
of thethat
jet stream,
which in
current
software.
ECMWF the
climate
model
has
highest
scale
of alert
as storm
Stephanie
rolled
in.
warm and cold weather anomalies,
Theturn
300mb
high
level winds
be
predicted
with
a certain
levelactive
of skillETC
in
output
toplays
nine
months
could
help
diagnose
and
predict
high-impact
a crucial
role incan
steering
European
ETCs.
During
with less than 50 miles between
The
300mb
high
level
winds
can
be
predicted
with
a
certain
level
of
skill
current
climate
model
software.
The
ECMWF
climate
model
that
has
seasons.
Additionally,
QBO, which
west-to-east
tracks,from
canin
phases,
the jet stream
tendsenhances
to be reinforced
andstorm
prevented
extended warm and cold fronts.
output
to
nine
months
could
help
and predict
high-impact
current
climate
model
Thediagnose
ECMWF
climate
model
that has
be
predicted
several
incalled
advance.
shifting.
This
is months
ansoftware.
effect
eddy feedback.
seasons.
QBO,
which
tracks, can
output toAdditionally,
nine months
could
helpenhances
diagnosewest-to-east
and predictstorm
high-impact
By maintaining
the months
shape
consistency
the jet stream,
eddy
feedback
be
predicted
several
in advance.
seasons.
Additionally,
QBO, and
which
enhances of
west-to-east
storm
tracks,
can
propensity
be increases
predicted the
several
monthsfor
in clustering
advance. of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
14 European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
14 4 14 14
Predictions
Under A Changing Climate
The Science of
European
Extratropical
The 2013-2014 European
winterAstorm
season had some
of the most
Predictions
Under
Changing
Climate
severe
sequences of storms since 1990. Given that some of this may be
Cyclones
ECHAM5-­‐CHRM ECHAM5-­‐CHRM ECHAM5-­‐CHRM The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
due to
climate change
and winter
resultant
altered
weather
the
The
2013-2014
European
season
hadpatterns,
some ofstudying
the most
Predictions
Under
A storm
Changing
Climate
Climatology
climate
change impact
on European
high priority.
severe
sequences
of storms
sinceETCs
1990.becomes
Given thata some
of this may be
due
climate change
andwinter
resultant
altered
weather
patterns,
Theto
2013-2014
European
storm
season
had some
of thestudying
most the
Schwierz
et
al.
conducted
a
study
that
used
three
different
climate
The
major
factors
driving
European
ETCs
are
the
Arctic
Oscillation
severe
sequences
of
storms
since
1990.
Given
that
some
of
this
may
be and
climate change impact on European ETCs becomes a high priority.
scenarios
forchange
Europe
to resultant
create
an
insurance
model.
State-of-the-art
North
Atlantic
Oscillation,
two climate
indices
for
the
Northern
Hemisphere.
due
to climate
and
altered
weatherloss
patterns,
studying
the
climatemodels
change
impact
on European
ETCs
becomes
a high
priority. climate
global
utilized
to
provide
estimates
of
thedifferent
uncertainties.
Schwierz
et al.were
conducted
a study
that
used three
Arcticfor
Oscillation
(AO)
scenarios
Europe to create
an insurance loss model. State-of-the-art
Schwierz et al. conducted a study that used three different climate
Over
the
past 30
years,
insured
naturalestimates
catastrophe
losses
have increased
global
models
were
utilized
to provide
the
uncertainties.
scenarios
for Europe
toto
create
an insurance
lossofmodel.
State-of-the-art
The Arctic
is home
a
semi-permanent
circulation
significantly.
While
factors
that
contribute to thelow
risepressure
include socioeconomic
global models were utilized to provide estimates of the uncertainties.
known
as
the
‘Polar
Vortex’,
which
rose
to
prominence
in
the
first quarter
Over
the past along
30 years,
insuredthe
natural
catastrophe
losses have
increased
development
coastlines,
frequency
of weather-related
of 2014.
The
is inthat
constant
opposition
to
(and
therefore
Over
the past
30 Vortex
years,
insured
catastrophe
losses
have
increased
significantly.
While
factors
contribute
to the rate.
rise
include
socioeconomic
catastrophes
has
increased
at natural
a
corresponding
Schwierz
et represents
al.’s
significantly.
While
factors
that
contribute
to
the
rise
include
socioeconomic
opposing
pressure
to)
the
weather
patterns
of
the
northern
middle
study takes the
demographic
shifts
into mind
when analyzing thelatitudes
development
along
coastlines, the
frequency
of weather-related
development
along
coastlines,
the frequency
ofnorthern
weather-related
(i.e.
Northern
Europe,
Northern
Asia
and
North America).
impacts of climate
changeatona European
ETCs.
catastrophes
has increased
corresponding
rate. Schwierz
et al.’s
catastrophes has increased at a corresponding rate. Schwierz et al.’s
study takes the demographic shifts into mind when analyzing the
study
the demographic
shifts
into
mind when
analyzing
AO takes
measures
the variation
in the
strength,
intensity
andthe
size of the jet
HC-­‐CHRM impacts
climate
changeononEuropean
European
ETCs.
HC-­‐CLM impacts of
of climate
change
ETCs.
stream as it expands and contracts to alter the shape of the fast-flowing
air current. AO is measured by opposing sea-pressure anomalies, ranging
HC-­‐CHRM HC-­‐CLM HC-­‐CHRM HC-­‐CLM th
from the Arctic Circle approximately to the 38 parallel.
During the ‘negative phase’ of AO, sea-level pressure is high in the
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
AO has the exact opposite pattern.
Dr. James E. Hansen of NASA describes AO thus:
"The degree to which Arctic air penetrates into middle latitudes is related to
the AO index, which is defined by surface atmospheric pressure patterns.
When the AO index is positive, surface pressure is low in the polar region.
This helps the middle latitude jet stream to blow strongly and consistently
from west to east, thus keeping cold Arctic air locked in the polar region.
When the AO index is negative, there tends to be high pressure in the polar
region, weaker zonal winds, and greater movement of frigid polar air into
Figure
10. Expected
climate change impact on ETC gust fields. Shown is the
middle
latitudes."
Figure
10. Expected
climate change impact on ETC gust fields. Shown is the
difference between historical CTL scenario (Oct 1961-Mar 1990) and the futuristic A2
difference between historical CTL scenario (Oct 1961-Mar 1990) and the futuristic A2
scenario
(Octa2071-Mar
2100)
by the IPCC.
Each
box represents
different which
AO has
dominant
rolesetinforth
determining
the
shape
of the jet astream,
Figure
10.
Expected
climate
change
impact
onIPCC.
ETC gust
Shown is the
scenario
(Oct
2071-Mar
2100)
set forth
by the
Eachfields.
box represents
a different
comparison of mean gust fields, given the three global climate model simulations
in
turn plays a crucial role in steering European ETCs. During active ETC
comparison
of mean
gust fields,
the three
global climate
model
simulations
difference
historical
CTLgiven
scenario
(Oct
1961-Mar
1990)
and the
futuristic A2
(from left tobetween
right,
ECHAM5-CHRM,
HC-CHRM,
HC-CLM).
phases, the jet stream tends to be reinforced and prevented from
(from left (Oct
to right,
ECHAM5-CHRM,
HC-CHRM,
HC-CLM).
scenario
2071-Mar
2100) set forth
by the IPCC.
Each box represents a different
The
most striking
impactcalled
is an increase
in wind gusts over a
shifting.
Thisclimate
is an effect
eddy feedback.
comparison of mean gust fields, given the three global climate model simulations
broad
band
that stretches
from the
eastern
North
over over
Greata
The
most
climate impact
is an
increase
inAtlantic,
wind gusts
(from
to striking
right, ECHAM5-CHRM,
HC-CHRM,
HC-CLM).
Byleft
maintaining
the shape
consistency
theECHAM5-CHRM
jet stream, eddy feedback
Britain
and into Northern
andand
Central
Europe. of
The
broad band that stretches from the eastern North Atlantic, over Great
climate
modelthe
extends
the wind
all the way
to Eastern
Europe.
increases
propensity
forfield
clustering
of ETCs.
Such
clustering
Britain
and
into Northern
and Central
Europe.inThe
ECHAM5-CHRM
The
most
striking
climate impact
is an increase
wind
gusts over a
This
area of increased
wind
is circumscribed
by two 1987,
parallel1990,
bands2000
of and 2014
patterns
were seen
during
the destructive
climate
model
extends
wind
field
all the North
way to
Eastern
Europe.
broad
band
stretches
from
the
eastern
Atlantic,
Great
reduced
guststhat
from
Spain the
to the
Eastern
Mediterranean
Sea
(in theover
South)
European ETC seasons. This is a month-to-month phenomenon. It does
This
area
of into
increased
wind
is circumscribed
by two
bands of
Britain
and
Northern
and
Central(inEurope.
Theparallel
ECHAM5-CHRM
and the
Northern
Atlantic
to Scandinavia
the North).
not persist on a yearly basis.
climate
extends
field all
the way to Eastern
reduced model
gusts from
Spainthe
to wind
the Eastern
Mediterranean
Sea (in Europe.
the South)
and the
Atlantic
to is
Scandinavia
(in the
North).
This
areaNorthern
of increased
wind
circumscribed
by two
parallel bands of
reduced gusts from Spain to the Eastern Mediterranean Sea (in the South)
15 Northern Atlantic to Scandinavia (in the North).
European Extratropical Cyclones | TransRe White Paper
and
the
15 European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
15 4 15
The
Science of European Extratropical
The figure from Schwierz et al’s study shows that regional gust models have
minor deviations over oceans, but considerable differences over land. Wind
Cyclones
gust projections differ by country and region, depending on climate model.
Climatology
Frequency of events are expected to increase over Southern
Scandinavia,
Great Britain,
SeaOscillation
and the English
The
major factorsNorthern
driving European
ETCs the
are North
the Arctic
and
Channel,
Germany
(particularly
over
Germany),
North
AtlanticBenelux,
Oscillation,
two climate
indices for
the Northern
Northern Hemisphere.
extending towards Poland and the Baltic States, with an additional
Arctic
Oscillation
(AO)
increase
over the Alps,
Southern Italy and the Adriatic Sea.
The
Arcticare
is home
to ato
semi-permanent
lowannual
pressure
Events
expected
increase average
losscirculation
over the 10-year
known
as
the
‘Polar
Vortex’,
which
rose
to
prominence
in The
the first
quarter
(23%), 30-year (50%) and 100-year (104%) timeframe.
expected
loss
of for
2014.
Vortex is events
in constant
opposition to (and
therefore
rareThe
high-impact
is disproportionately
large,
whererepresents
Germany
opposing
to) the(116%)
weather
patterns
of the northern
latitudes
(114%) pressure
and Denmark
see
the greatest
increasemiddle
in insured
loss
(i.e.
Northern
Europe,
Northern
Asia
and
northern
North
America).
in the 100-year model.
AOLoss
measures
the variation
the strength,
intensity
and size
of theand
jet
potentials
for Great in
Britain
and Germany
increase
by 37%
stream
it expandsindicating
and contracts
to alter
the shape
of the fast-flowing
21%, as
respectively,
a much
broader
loss distribution
with
current. AO
measured
by opposing sea-pressure anomalies, ranging
forismore
tail events.
Schwierz et al. generated a probabilistic airpotential
th
from
the
Arctic
Circle
approximately
to the 38 parallel.
event sets for different countries, using
Swiss Re’s insurance loss model as
event
setOscillation
inputs.
The
Arctic
helps define the
jet stream, which can send cold, polar
The resulting climate change impact for
air far south with its large oscillations.
wintertime windstorms is calculated and
This image compares December 2010
analyzed by country.
to the previous 10-year average,
showing
that
AO and
the shape
of the
Analysis
shows
average
expected
loss
jetincreases
stream altered
the
temperature
in all countries except
gradient
Ireland.in the Northern Hemisphere.
Arctic air was sent as far south as the
Largest increases
are in
Denmark
Carolinas
and Portugal.
Red
(blue) and
Germany,
which
situated
indicates
areas
thatare
areboth
warmer
within the
of strongest
gust
(colder)
thanband
average.
Note how
the jet
increases
over the
North
stream’s
strange
shape
canSea.
juxtapose
warm and cold weather anomalies,
with
less than 50 miles between
extended warm and cold fronts.
During the ‘negative phase’ of AO, sea-level pressure is high in the
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
AO has the exact opposite pattern.
Dr. James E. Hansen of NASA describes AO thus:
"The degree to which Arctic air penetrates into middle latitudes is related to
the AO index, which is defined by surface atmospheric pressure patterns.
When the AO index is positive, surface pressure is low in the polar region.
This helps the middle latitude jet stream to blow strongly and consistently
from west to east, thus keeping cold Arctic air locked in the polar region.
When the AO index is negative, there tends to be high pressure in the polar
Figure 11. Climate change impact on annual expected loss, for selected regional
region, weaker zonal winds, and greater movement of frigid polar air into
markets given Swiss Re’s insurance loss model. Error bars encompass results of the
middle latitudes."
three model chains considered. (CTL=Control).
AO has a dominant role in determining the shape of the jet stream, which in
In the A2 scenario simulation, the maximum wind increase is of 6-8%
turn plays a crucial role in steering European ETCs. During active ETC
from the English Channel to the German Bight. The general areas of
phases, the jet stream tends to be reinforced and prevented from
increased gusts extend that corridor, from Western to Central Europe.
shifting. This is an effect called eddy feedback.
A2 simulations also show an increase in the overall number of ETC
By maintaining the shape and consistency of the jet stream, eddy feedback
events, assuming climate change and global warming scenarios.
increases the propensity for clustering of ETCs. Such clustering
patterns
seen
during the
destructive
1990,of2000
and 2014
We canwere
expect
an increase
of intensity
and1987,
frequency
wintertime
ETCs.
European
ETC
seasons.
This
is
a
month-to-month
phenomenon.
It
does
This will correspond to more windstorms tracking along the corridor
notfrom
persist
on aBritain
yearly to
basis.
Great
Germany via the Netherlands
In other words, the regions with the highest total gross premiums
written can expect more detrimental activity from European ETCs.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
4 16 16
Insurance Case Study: Parametric Rolling
and Post-Panamax Containerships
The
Science
of
European
Extratropical
Since
the
1950’s,
containerships
have
grown in
size with the
expansion
of
Insurance
Insurance
Case
Case
Study:
Study:
Parametric
Parametric
Rolling
Rolling
global trade. 14,000 containerships pass through the Panama Canal
Cyclones
and Post-Panamax
and Post-Panamax
Containerships
Containerships
every year, carrying grain, oil and manufactured goods.
Climatology
Since
the
Since
1950’s,
the containerships
1950’s,
containerships
have
grown
haveresulted
ingrown
size with
in
the with
expansion
the expansion
of
of
The
expansion
of the Panama
Canal
has
in size
massive
dredging
global
trade.
global
14,000
trade.
containerships
14,000
containerships
pass
through
pass
through
the
Panama
the
Panama
Canal
Canal
projects
the installation
of largerETCs
load are
systems
at ports
around the
The
majorand
factors
driving European
the Arctic
Oscillation
andworld
every
year,
every
carrying
year, for
carrying
grain,
oilgrain,
andof
manufactured
oil
and manufactured
goods.
goods.
as
they
prepare
the
arrival
post-Panamax
and
New
Panamax
ships.
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
The How
expansion
The
expansion
of the
Panama
oftothe
Panama
Canal has
Canal
resulted
has
resulted
in massive
inportion
massive
dredging
does
this
relate
European
ETCs?
A significant
ofdredging
global
Arctic
Oscillation
(AO)
projects
projects
and
the
and
installation
the
installation
of
larger
of
load
larger
systems
load
systems
at
ports
at
around
ports
the
around
world
the world
trade crosses the North Atlantic Ocean. If containerships take that route
as they
prepare
as
they
prepare
for
the
arrival
for
the
of
arrival
post-Panamax
of
post-Panamax
and
New
and
Panamax
New
Panamax
ships.
ships.
between
and
they run thelow
riskpressure
of experiencing
high winds
The
ArcticNovember
is home to
a March,
semi-permanent
circulation
and waves
during
theVortex’,
winter windstorm
season.
known
as the
‘Polar
which rose
to prominence in the first quarter
How does
How
thisdoes
relate
thistorelate
European
to European
ETCs? A
ETCs?
significant
A significant
portion portion
of global
of global
of 2014. The Vortex is in constant opposition to (and therefore represents
trade
tradeAPL
crosses
theChina
North
the
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North
Atlantic
Ocean.
Ocean.
If containerships
Ifoverboard
containerships
take
thattake
In crosses
1998,
lost
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when
itroute
wasthat route
opposing pressure to) the weather patterns of the northern middle latitudes
Global trade routes emphasize the
between
between
November
November
andBabs,
March,
and
they
March,
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high winds
struck
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demonstrating
ships
are
Northern Europe, Northern Asia and northern North America).
passage across the North Atlantic, evenand(i.e.
waves
and
during
waves
the
during
winter
the
windstorm
winter
windstorm
season.
season.
vulnerable to a phenomenon known as ‘parametric rolling’. This occurs
during the winter months when ETCs
when
waves above
a certainin
threshold
or critical
height come
exactly
twice
AO
measures
the variation
the strength,
intensity
and size
of the
jet
are more likely to form, intensify and
In 1998,InAPL
1998,
China
APLlost
China
a number
lost a number
of containers
of containers
overboard
overboard
when it was
when it was
as
fast
as
a
ship’s
roll
period.
Global trade
Globalroutes
trade emphasize
routes emphasize
the
the
stream as it expands and contracts to alter the shape of the fast-flowing
cluster.
struck bystruck
Typhoon
by Typhoon
Babs, demonstrating
Babs, demonstrating
that post-Panamax
that post-Panamax
ships are
ships are
passage
passage
across across
the North
theAtlantic,
North Atlantic,
even evenair current. AO is measured by opposing sea-pressure anomalies, ranging
vulnerable
vulnerable
to
a
phenomenon
to
a
phenomenon
known
as
known
‘parametric
as
‘parametric
rolling’.
rolling’.
This
occurs
This occurs
Parametric rolling can occur in stern-quartering
th or bow-quartering seas.
during
the months
winter months
when ETCs from
during the
winter
when ETCs
the Arctic Circle approximately to the 38 parallel.
when
waves
when
above
waves
a
above
certain
a
threshold
certain
threshold
or
critical
or
height
critical
come
height
exactly
come
twice
exactly
Cargo on post-Panamax ships is particularly vulnerable to be lost in these twice
arelikely
moretolikely
form, intensify
and
are more
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and
as fast
as
asbecause
afast
ship’s
as aroll
period.
roll period.
seas,
ofship’s
the
U-shape,
bow and wide
beamisofhigh
the oversized,
During
the
‘negative
phase’
offlared
AO, sea-level
pressure
in the
cluster.cluster.
post-Panamax
hull.
The Arctic Oscillation helps define the
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
Parametric
Parametric
rolling can
rolling
occur
can
inoccur
stern-quartering
in stern-quartering
or bow-quartering
or bow-quartering
seas. seas.
AO has the exact opposite pattern.
jet stream, which can send cold, polar
Cargo
on
Cargo
post-Panamax
on
post-Panamax
ships
is
ships
particularly
is
particularly
vulnerable
vulnerable
to
be
lost
to
in
bethese
lost
In APL China litigation, the expert witnesses proved that in certain
sea in these
air far south with its large oscillations.
seas,
because
seas, because
the U-shape,
of of
theNASA
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flared
bow
flared
and
bow
wide
and
beam
wideofto
beam
the
oversized,
of the oversized,
conditions,
post-Panamax
ships
are
especially
prone
parametric
Dr.
James
E.of
Hansen
describes
AO
thus:
This image compares December 2010
post-Panamax
post-Panamax
hull. phenomenon whereby large roll angles are
rolling,
or, hull.
the unstable
to the previous 10-year average,
"The
degree
to significant
which Arcticpitch
air penetrates
coupled
with
motions. into middle latitudes is related to
showing that AO and the shape of the In APL
China
In APL
litigation,
China
litigation,
the
expert
theby
witnesses
expert
witnesses
proved
that
proved
inpressure
certain
that in sea
certain
sea
the AO
index,
which
is defined
surface
atmospheric
patterns.
jet stream altered the temperature
Parametric
extreme
stresses
ontoprone
containerships
and
conditions,
conditions,
post-Panamax
post-Panamax
ships are
ships
especially
are
especially
prone
parametric
When
the
AOrolling
index
isintroduces
positive,
surface
pressure
is low
inparametric
the to
polar
region.
gradient in the Northern Hemisphere.
their
securing
systems,
and
it
differs
dynamically
from
synchronous
rolling.
rolling,
rolling,
or,
the
unstable
or,
the
unstable
phenomenon
phenomenon
whereby
whereby
large
roll
large
angles
roll
are
angles
are
This helps the middle latitude jet stream to blow strongly and consistently
Stormy
conditions
can
cause
steerage
to
completely
lost.region.
Arctic air was sent as far south as the
coupled
coupled
with
withthus
significant
pitch
motions.
pitch
motions.
from
west
tosignificant
east,
keeping
cold
Arctic
airbe
locked
in the polar
Carolinas and Portugal. Red (blue)
When the AO index is negative, there tends to be high pressure in the polar
Of particular
interest
is that
normal,
40ft
waves
of acontainerships
certain
wave-period
Parametric
Parametric
rolling
introduces
rolling
introduces
extreme
extreme
stresses
stresses
on
on containerships
and
and
indicates
areas
that
are
warmer
weaker zonal winds, and greater movement of frigid polar air into
The Ital Florida is example of one of the region,
can
cause
a post-Panamax
containership
to from
heel synchronous
more
than
40rolling. rolling.
their
securing
their
securing
systems,
systems,
and
it
differs
and
it
dynamically
differs
dynamically
from
synchronous
(colder)
than average.
Notestaggered
how the jet
latitudes."
containerships
that have
into middle
degrees.
It isn’t
necessary
freak steerage
waves,
monsterwellen,
Stormy
Stormy
conditions
conditions
can cause
canfor
steerage
cause
to be or
completely
to
be completely
lost. to cause
lost. steel
stream’s
strange
shape
can
port after being whipped byjuxtapose
the ‘watery
lashings to lose their hold on large loads.
AO has a dominant role in determining the shape of the jet stream, which in
warm
and coldofweather
wilderness’
Hermananomalies,
Melville’s
Of particular
Of particular
interest interest
is that normal,
is that normal,
40ft waves
40ft of
waves
a certain
of a certain
wave-period
wave-period
turn
plays a crucial role in steering European ETCs. During active ETC
The
Italless
The
Florida
Ital Florida
is50
example
is example
of one of
of the
one of can
the Litigation
with
than
miles
between
for theaAPL
China
endedcontainership
in 2003;
proof
ofthan
parametric
mythos.
cause
canacause
post-Panamax
post-Panamax
containership
to the
heel
more
to heel
more
40than rolling
40
phases,
the jet
stream tendsand
to allowed
be reinforced
and prevented
from
extended
warm
cold
fronts.
containerships
containerships
thatand
have
that
staggered
have
staggered
into
into
helped
limit
APL’s
formonsterwellen,
a smaller
settlement.
Since
degrees.
degrees.
It isn’t
necessary
It isn’t liability
necessary
for freakfor
waves,
freak or
waves,
or monsterwellen,
to cause
tosteel
cause steel
shifting.
This is anrolling
effecthas
called eddyexplain
feedback.
port
afterwhipped
being whipped
by the ‘watery
port after
being
by the ‘watery
then,
lashings
lashings
toparametric
lose their
to lose
hold
their
on hold
largehelped
on
loads.
large loads. what happened on the
wilderness’
of Herman
Melville’s
wilderness’
of Herman
Melville’s
Maersk Carolina, P&O Nedlloyed Genoa and CMA CGM Otello and
By maintaining the shape and consistency of the jet stream, eddy feedback
Litigation
Litigation
for
the APL
for the
China
APL
ended
Chinainended
2003;inthe
2003;
proof
theofproof
parametric
of parametric
rolling rolling
mythos.mythos.
many
other
maritime
mysteries.
increases the propensity for clustering of ETCs. Such clustering
helped limit
helped
APL’s
limitliability
APL’s liability
and allowed
and allowed
for a smaller
for a settlement.
smaller settlement.
Since Since
patterns were seen during the destructive 1987, 1990, 2000 and 2014
then, parametric
then, parametric
rolling has
rolling
helped
has explain
helped explain
what happened
what happened
on the on the
European ETC seasons. This is a month-to-month phenomenon. It does
Maersk Maersk
Carolina,
Carolina,
P&O Nedlloyed
P&O Nedlloyed
Genoa and
Genoa
CMA
and
CGM
CMA
Otello
CGMand
Otello and
not persist on a yearly basis.
many other
manymaritime
other maritime
mysteries.
mysteries.
17 European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
White Paper
EuropeanEuropean
Extratropical
Extratropical
CyclonesCyclones
| TransRe
| TransRe
White Paper
17 4 17 17
The Science of European Extratropical
Implications for Insurers
Cyclones
As sophisticated insurance markets continue to thrive in Western Europe
Climatology
and
insurance penetration expands in Central and Eastern Europe, midlatitude weather patterns remain unpredictable.
The major factors driving European ETCs are the Arctic Oscillation and
Northcountless
Atlantic Oscillation,
two climate
indices predict
for the tropical
Northernstorm
Hemisphere.
While
projects attempt
to accurately
intensification, only modest improvements are made; anticipating nonArctic Oscillation (AO)
tropical storm path and strength is even more difficult. Clashing weather
systems often lead to extreme weather that can only be forecasted up to
The Arctic is home to a semi-permanent low pressure circulation
two weeks in advance.
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
of 2014.
The
Vortex
is in October
constantand
opposition
to (andbraces
therefore
represents
Thus,
every
year
between
April, Europe
itself
against
opposing
pressure
to)
the
weather
patterns
of
the
northern
middle
what could be a powerful winter storm season. It is not uncommon latitudes
for
(i.e. Northern Europe, Northern Asia and northern North America).
ETCs to lash the continent with winds over 100mph, sending trees,
scaffolding and buildings to their demise.
AO measures the variation in the strength, intensity and size of the jet
stream
it expands
and contracts
to alter
theit shape
of the to
fast-flowing
Given
the as
destruction
caused
by European
ETCs,
is important
inform
air
current.
AO
is
measured
by
opposing
sea-pressure
anomalies,
ranging
and prepare our industry of the financial and
social
impact
of
these
th
from
the
Arctic
Circle
approximately
to
the
38
parallel.
weather patterns.
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
phase’
AO,and
sea-level
pressure
is high
in the
It During
is clearthe
that‘negative
NAO, AO,
MJO, of
QBO
the 300mb
high-level
wind
Arctic
and
low
in
the
northern
middle
latitudes.
The
‘positive
phase’
anomalies show distinct effects on extratropical storm path, intensity,of
AO has the exact opposite pattern.
clustering and frequency. A combination of each climate index phase and
signal corresponds to a greater or lesser percentage of ETC landfall along
Dr. James E. Hansen of NASA describes AO thus:
certain sections of the European coastline, with the ability to continue into
the
continent.
"The
degree to which Arctic air penetrates into middle latitudes is related to
the AO index, which is defined by surface atmospheric pressure patterns.
Assuming climate change scenarios, society should be equipped for
When the AO index is positive, surface pressure is low in the polar region.
the worst case scenarios. Climate change will not act as a ‘Doomsday
This helps the middle latitude jet stream to blow strongly and consistently
Device’ i.e. Dr. Strangelove, but altered climate interactions are indubitably
from west to east, thus keeping cold Arctic air locked in the polar region.
changing global weather patterns.
When the AO index is negative, there tends to be high pressure in the polar
region,
weaker
zonalhow
winds,
and work
greater
frigid
polar air into
Our
research
shows
much
is movement
being doneofby
governments
middle
latitudes."
and private institutions to develop more comprehensive regional
climate models that incorporate and weigh all the pertinent climate
AO has a dominant role in determining the shape of the jet stream, which in
indices, climate signals and risk exposures.
turn plays a crucial role in steering European ETCs. During active ETC
the
jet stream
to be and
reinforced
from
Asphases,
research
continues,
so tends
consumers
insurersand
will prevented
be more informed,
shifting. This is an effect called eddy feedback.
adjusting their insurance and reinsurance buying habits to accommodate
new scientific findings. Based on the available data, it would be wise to
By maintaining the shape and consistency of the jet stream, eddy feedback
anticipate more intense and more frequent European ETCs.
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
4 18 18
The Science of European Extratropical
Glossary
Cyclones
Arctic Oscillation- An index of the dominant sea-level pressure variations
0
Climatology
between
the North Pole and 45 N.
Azores
High-factors
A largedriving
subtropical
semi-permanent
center
high pressure
The major
European
ETCs are the
ArcticofOscillation
and
centered
over theOscillation,
Azores. Also
asindices
the Bermuda
North Atlantic
twoknown
climate
for the High.
Northern Hemisphere.
Arctic AOscillation
(AO)
Cold-corecyclone associated
with a cold pool of air residing at the
storm’s center high in the troposphere.
The Arctic is home to a semi-permanent low pressure circulation
Convectivestorm
characterized
by the
presence
of lighting
andfirst
thunder.
known asAthe
‘Polar
Vortex’, which
rose
to prominence
in the
quarter
of 2014. The Vortex is in constant opposition to (and therefore represents
Disturbance- An unstable creates a variation from normal wind conditions.
opposing pressure to) the weather patterns of the northern middle latitudes
(i.e.feedbackNorthern Europe,
Northern
Asia keeps
and northern
North America).
Eddy
The feedback
system
the jet stream
from shifting.
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
AO measures
the variation
in the strength,
intensity
and size
of the jet
Extratropical
CycloneMiddle latitude
cyclones that
have distinct
fronts
stream
as
it
expands
and
contracts
to
alter
the
shape
of
the
fast-flowing
and horizontal gradients in temperature and dew point.
air current. AO is measured by opposing sea-pressure anomalies, ranging
th
from the
Arctic
Circle approximately
to the 38
parallel.
Icelandic
LowSemi-permanent
low pressure
system
centered between
Iceland and southern Greenland.
During the ‘negative phase’ of AO, sea-level pressure is high in the
JetArctic
StreamFast
narrow airmiddle
currents
found in The
the atmosphere.
The of
and
lowflowing,
in the northern
latitudes.
‘positive phase’
shape
of the
jet stream
influence local weather patterns.
AO and
has location
the exact
opposite
pattern.
Dr. James E. Oscillation-Major
Hansen of NASA describes
AO thus: (30-90 days)
Madden-Julian
part of intraseasonal
variability in the tropical atmosphere. Travels east from Indian Ocean.
"The degree to which Arctic air penetrates into middle latitudes is related to
North
OscillationClimactic
phenomenon
that measures
the Atlantic
AO index,
which is defined
by surface
atmospheric
pressure the
patterns.
atmospheric
between
Icelandic
and Azores
When the difference
AO index is
positive,
surface low
pressure
is low high.
in the polar region.
This helps the middle latitude jet stream to blow strongly and consistently
Occluded
FrontFormed
a cold
front
overtakes
from west
to east,
thus during
keepingcyclogenesis,
cold Arctic airwhen
locked
in the
polar
region.
a warm
front.
They
usually
form
around
mature
low
pressure
areas.
When the AO index is negative, there tends to be high pressure in the polar
region, weaker zonal winds, and greater movement of frigid polar air into
Parametric Rolling- The phenomenon where large roll angles are coupled
middle latitudes."
with significant pitch motions. These can be prompted by normal size waves.
AO has a dominant role in determining the shape of the jet stream, which in
Polar Vortex- The semi-permanent and large-scale cyclone located near the
turn plays a crucial role in steering European ETCs. During active ETC
planet’s geographic North Pole.
phases, the jet stream tends to be reinforced and prevented from
This is anAtmospheric
effect called
eddy feedback.
Seashifting.
Level Pressurepressure
at sea level.
By maintaining
thethat
shape
andaconsistency
of the jet stream,
eddythe
feedback
SinusoidalA curve
shows
repetitive oscillation,
named after
sine
increases the propensity for clustering of ETCs. Such clustering
function.
patterns were seen during the destructive 1987, 1990, 2000 and 2014
Tropical
CycloneTropical latitude
fueled by high
sea surfaceIt does
European
ETC seasons.
This iscyclone
a month-to-month
phenomenon.
temperatures
and
vertical
temperature
gradients.
not persist on a yearly basis.
Warm-core-A cyclone whose central core has a higher potential energy than
the general circulation around it.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
19 4 19
The Science of European Extratropical
Contacts
Cyclones
To discuss any of the contents of this paper, please contact:
Climatology
James Rohman
Global Catastrophe Management, New York
The major factors driving European ETCs are the Arctic Oscillation and
North Atlantic
Oscillation,
T: 1 (212)
365 2438two climate indices for the Northern Hemisphere.
E: [email protected]
Arctic Oscillation (AO)
Arctic
home to a of
semi-permanent
low pressure
circulation
ToThe
discuss
theisimplications
this paper, and your
reinsurance
needs in
known
as
the
‘Polar
Vortex’,
which
rose
to
prominence
in
the
first quarter
response, please contact:
of 2014. The Vortex is in constant opposition to (and therefore represents
Geoff
Peachto) the weather patterns of the northern middle latitudes
opposing
pressure
TransRe
LondonNorthern Asia and northern North America).
(i.e. Northern Europe,
T: +44-20-7204-8607
AO measures
the variation in the strength, intensity and size of the jet
E: [email protected]
stream as it expands and contracts to alter the shape of the fast-flowing
air current. AO is measured by opposing sea-pressure anomalies, ranging
th
from the
Arctic
Circle approximately to the 38 parallel.
Lorne
Zalkowitz
TransRe Zurich
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and
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the6104
northern middle latitudes. The ‘positive phase’ of
+41
44in
227
E:the
[email protected]
AO has
exact opposite pattern.
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
Dr. James E. Hansen of NASA describes AO thus:
Bertrand Levy
"The degree
to which
TransRe
Paris Arctic air penetrates into middle latitudes is related to
the AO index, which is defined by surface atmospheric pressure patterns.
1 4006
When T:
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E: [email protected]
This helps the middle latitude jet stream to blow strongly and consistently
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AO hasE:[email protected]
dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
Krzysztof Koperski
shifting. This is an effect called eddy feedback.
TransRe Warsaw
By maintaining the shape and consistency of the jet stream, eddy feedback
T: +48 22 630 63 71
increases
the propensity for clustering of ETCs. Such clustering
E: [email protected]
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
20 4 20
The Science of European Extratropical
Citations
Cyclones
Accuweather
Climatology
Associated Press. Cover image shows winter storm Stephanie lashing
th
The major
European
are theFebruary
Arctic Oscillation
and
Douro’s
riverfactors
mouth driving
in Porto,
PortugalETCs
on Monday,
10 , 2014.
North Atlantic Oscillation, two climate indices for the Northern Hemisphere.
Cameron Beccario, creator of http://earth.nullschool.net/.
Arctic Oscillation (AO)
Designed by Inc Design
The Arctic is home to a semi-permanent low pressure circulation
Ianknown
Bell and
Martin
Visbeck,
Lamont-Doherty
Earth Observatory
at quarter
as the
‘Polar
Vortex’,
which rose to prominence
in the first
Columbia
University’s
Earth
Institute.
of 2014. The Vortex is in constant opposition to (and therefore represents
http://www.ldeo.columbia.edu/res/pi/NAO/
opposing pressure to) the weather patterns of the northern middle latitudes
(i.e. Northern Europe, Northern Asia and northern North America).
Lin, Brunet and Derome., ‘An observed connection between the North
Atlantic
Oscillation
and
the Madden-Julian
Oscillation’,
Journal
of Climate.
AO measures
the
variation
in the strength,
intensity
and size
of the jet
stream as it expands and contracts to alter the shape of the fast-flowing
NASA
air current. AO is measured by opposing sea-pressure anomalies, ranging
th
from the
Arctic Circle
approximately
NOAA’s
Climate
Prediction
Center to the 38 parallel.
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
DuringMagazine
the ‘negative phase’ of AO, sea-level pressure is high in the
Outside
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
Professor
Mike
Wallace,
Professor
Emeritus, Department of Atmospheric
AO has the
exact
opposite
pattern.
Sciences, University of Washington.
Dr. James E. Hansen of NASA describes AO thus:
Risk Prediction Initiative at Bermuda Institute of Ocean Sciences,
"The degree
to which and
Arctic
penetrates
middle latitudes
is related to
‘European
Windstorms
theairNorth
Atlanticinto
Oscillation:
Impacts,
the AO index,and
which
is defined by surface atmospheric pressure patterns.
Characteristics
Predictability’
When the AO index is positive, surface pressure is low in the polar region.
UKThis
Methelps
Office,
of Reading
and to
University
of Exeter.
Licensed
theUniversity
middle latitude
jet stream
blow strongly
and consistently
under
Commons
CC BY cold
4.0 International
License
fromCreative
west to east,
thus keeping
Arctic air locked
in the polar region.
When the AO index is negative, there tends to be high pressure in the polar
region, weaker zonal winds, and greater movement of frigid polar air into
middle latitudes."
AO has a dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
shifting. This is an effect called eddy feedback.
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
4 21 21
The Science of European Extratropical
Cyclones
Copyright and Disclaimers
Climatology
The material and conclusions contained in this document are for information
The
major only
factors
European
are the Arctic
and of its
purposes
anddriving
the authors
offerETCs
no guarantee
for theOscillation
completeness
North
Atlantic
Oscillation,
two
climate
indices
for
the
Northern
Hemisphere.
contents. The statements in this document may provide current expectations
of future events based on certain assumptions. These statements involve
Arctic
Oscillation (AO)
The Arctic Oscillation helps define the
jet stream, which can send cold, polar
air far south with its large oscillations.
This image compares December 2010
to the previous 10-year average,
showing that AO and the shape of the
jet stream altered the temperature
gradient in the Northern Hemisphere.
Arctic air was sent as far south as the
Carolinas and Portugal. Red (blue)
indicates areas that are warmer
(colder) than average. Note how the jet
stream’s strange shape can juxtapose
warm and cold weather anomalies,
with less than 50 miles between
extended warm and cold fronts.
known and unknown risks, uncertainties and other factors which are not
exhaustive.
authors
this document undertake
no obligation
to publicly
The
Arctic isThe
home
to a of
semi-permanent
low pressure
circulation
revise
or
update
any
statements,
whether
as
a
result
of
new
information,
known as the ‘Polar Vortex’, which rose to prominence in the first quarter
future
events
or otherwise
and in no
event shall
Transatlantic
of
2014.
The Vortex
is in constant
opposition
to (and
therefore Reinsurance
represents
Companypressure
or any ofto)
itsthe
affiliates
or employees
for any
damage
and
opposing
weather
patterns of be
theliable
northern
middle
latitudes
financial
loss Europe,
arising inNorthern
connection
use of North
the information
(i.e.
Northern
Asiawith
andthe
northern
America).relating to
this document.
AO measures the variation in the strength, intensity and size of the jet
About TransRe
stream
as it expands and contracts to alter the shape of the fast-flowing
air current. AO is measured by opposing sea-pressure anomalies, ranging
TransRe is the brand name for Transatlantic Holdings,
Inc. and its subsidiaries.
th
from the Arctic Circle approximately to the 38 parallel.
TransRe, wholly owned by Alleghany Corporation (NYSE-Y), is a reinsurance
organization
headquartered
in New
York
with operations
worldwide.
Since
During
the ‘negative
phase’
of AO,
sea-level
pressure
is high in
the
1978,
TransRe
has
been
offering
its
clients
the
capacity,
expertise
and
Arctic and low in the northern middle latitudes. The ‘positive phase’ of
creativity
necessary
to structure
programs across the full spectrum of property
AO
has the
exact opposite
pattern.
and casualty risks.
Dr. James E. Hansen of NASA describes AO thus:
Visit www.transre.com for additional information.
"The degree to which Arctic air penetrates into middle latitudes is related to
© 2014
Transatlantic
Inc.
All rights
reserved.pressure patterns.
the
AO index,
which isHoldings,
defined by
surface
atmospheric
When the AO index is positive, surface pressure is low in the polar region.
This helps the middle latitude jet stream to blow strongly and consistently
from
west to east, thus keeping cold Arctic air locked in the polar region.
TransRe
When
the AOPlaza
index is negative, there tends to be high pressure in the polar
One Liberty
region,
weaker
165 Broadway zonal winds, and greater movement of frigid polar air into
middle
latitudes."
New York,
New York 10006
AO has a dominant role in determining the shape of the jet stream, which in
turn plays a crucial role in steering European ETCs. During active ETC
phases, the jet stream tends to be reinforced and prevented from
shifting. This is an effect called eddy feedback.
By maintaining the shape and consistency of the jet stream, eddy feedback
increases the propensity for clustering of ETCs. Such clustering
patterns were seen during the destructive 1987, 1990, 2000 and 2014
European ETC seasons. This is a month-to-month phenomenon. It does
not persist on a yearly basis.
European Extratropical Cyclones | TransRe White Paper
European Extratropical Cyclones | TransRe White Paper
4 22 22