Download Is it true that the North Atlantic current could shut down?

Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
•
Natural variability can be classified by its forcing type (internal or
external to the climate system) and whether it is periodic/cyclic or
episodic.
Modes of Natural Variability that we know of:
timescale
1. Seasonal
90 days
2. El Niño Southern Oscillation
3-5 yrs
3. North Atlantic Oscillation
decadal
4. Volcanism
none
5. Ice ages
40,000 yrs
6. Pacific Decadal
20-50 yrs
form forcing
cyclic external
cyclic internal
cyclic internal??
episodic external
cyclic internal
cyclic ????
Ocean structure: on average:
warm and relatively fresh
mixed layer lying on top
of a nearly isothermal
(same temperature) cold
and salty water mass
Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
Air-Sea Interactions:
Ocean and atmosphere
communicate with one
another:
1. constituents: water
(precipitation and
evaporation), carbon dioxide,
oxygen, trace gasses, etc
2. Energy – momentum through
wind stress driving the
surface currents
3. Heat – sensible heat and
latent heat due to evaporation
http://science.hq.nasa.gov/oceans/images/
water_cycle.jpg
How does ocean circulation affect local climates?
Answer: Heat release locations are warmer!
http://
www.
wbgu
.de/I
mage
s/sn_
2006
_en/2
.14.png
Warm surface current- Less Dense
Cold deep water current–More Dense
Salty water anywhere- More Dense
Intergovernmental Panel on Climate Change (IPCC), "Climate Change 2001: The Scientific Basis"
What directions do warm and cold
water currents travel?
Is it true that the North Atlantic
current could shut down?
The ocean surface transfers heat to the atmosphere!
Animation by Jack Cook (Woods Hole Oceanographic Institute)
Animation by Jack Cook (Woods Hole Oceanographic Institute)
Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
What process could change the
ocean circulation?
http://www.whoi.edu/page.do?pid=12455&tid=282&cid=10046
go to bookmarks
The global thermohaline circulation: Cold Salty water in the
north Atlantic becomes dense and convects downward, spreads
southward and contributes to vertical overturning of deep ocean
water on millennial timescales.
Importance: Climate of northern Europe and Asia rely on heat
and moisture supplied to atmosphere to keep climate habitable
in extreme northern latitudes.
Is freshwater increasing in the
North Atlantic?
• http://www.whoi.edu/templates/files/multim
edia.jsp?pid=12455&cid=7466&cl=6732
•
Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
Even though the oceans and atmosphere are both fluids, they have
a fundamental difference – their density: Atmosphere 1 kg/cubic
meter, Ocean – approximately 1000 kg/cubic meter.
This density difference leads to large difference in heat capacity.
Heat capacity is defined as the amount of temperature change in
kelvin degrees for a unit input of heat energy.
The ocean’s heat capacity is approximately 41 times that of the
atmosphere.
A 1 degree change in atmospheric temperature is equivalent to an
0.02 change in ocean temperature change.
http://www.whoi.edu/institutes/occi/images/occi_abrclimate_jk_lev_en.gif
Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
El Nino is an example of air-sea interactions that occur on annual
time scales
Note figures 4.8 and 4.9:
Sea surface temperature (SST) patterns change fundamentally
with the el nino cycle
The atmosphere both forces and responds to the el nino cycle.
Normal sst patterns: atmospheric forcing of sst is accomplished
through easterly trade winds cooling the central and eastern
equatorial pacific. Atmosphere responds to warm western pacific
water by the occurrence of strong thunderstorms in that region
http://teacherresourceexchange.org/science/coriolis/index.php
ENSO Outline
ENSO Animation
•
•
http://www.cpc.noaa.gov/
products/precip/CWlink/
MJO/enso.shtml#curren
t
http://sealevel.jpl.nasa.gov/science/images/el-nino-la-nina.jpg
•
•
Mean state of the ocean and atmosphere across the tropical Pacific
Mean ocean surface temperatures
Mean tropical Pacific rainfall, winds, and subsurface ocean temperatures
Mean wintertime jet streams over the North Pacific and South Pacific
The ENSO cycle
El Niño and La Niña Ocean Temperature Patterns
The Southern Oscillation and its link to the ENSO cycle
The Southern Oscillation Index (SOI)
El Niño
El Niño (ENSO) related rainfall patterns over the tropical Pacific
El Niño-related winds, the state of the equatorial Walker circulation, subsurface ocean
structure
El Niño-related global temperature and rainfall patterns
El Niño - related changes in atmospheric circulation in the subtropics and middle
latitudes
La Niña
La Niña-related rainfall patterns over the tropical Pacific
La Niña-related winds, the state of the equatorial Walker circulation, subsurface
ocean structure
La Niña-related global temperature and rainfall patterns
La Niña- related changes in atmospheric circulation in the subtropics
2. Mean tropical Pacific rainfall, winds,
and subsurface ocean temperatures
•
NOAA Image
and text
•
NOAA Image
and text
Summary:
Normally in the equatorial pacific
El Niño and La Niña Ocean
Temperature Patterns
• Trade winds blow from the east to the west
• Warm water piles up on the western side of the
equatorial pacific ocean
• Cool water upwells along the coast of South
America
• Low pressure is observed over Indonesia and
the western pacific ocean and heavy rainfall
occurs there
• High pressure is observed in the eastern pacific
ocean.
•
The Southern Oscillation and its link to the ENSO
cycle
•
NOAA Image
and text
How are high and low pressures
related to rainfall and winds?
NOAA Image
and text
Pressure Force
• More air on the left
hand side (higher
pressure).
• The pressure
difference over that
distance of the
sheet (the pressure
gradient force),
pushes the sheet to
the right.
Pressure Force
• More air on the left
hand side (higher
pressure).
• The pressure
difference on either
side of the parcel
(the pressure
gradient force),
pushes the parcel to
the right.
Pressure Gradient Force
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/pgf.rxml
Ifhttp://teacherresourceexchange.org/science/coriolis/index.php
the earth was not spinning,
air would move directly from high
to low pressure areas.
Coriolis Force
http://teacherresourceexchange.org/science/coriolis/index.php
El Nino Related Rainfall
•
NOAA Image
and text
http://ww2010.at
mos.uiuc.edu/(Gh
)/guides/mtr/fw/gif
s/coriolis.mpg
Video
2. Mean tropical Pacific rainfall, winds,
and subsurface ocean temperatures
•
NOAA Image
and text
El Niño-related winds, the state of the equatorial
Walker circulation, subsurface ocean structure
Ocean productivity and El Niño
– easterly trade winds weaken,
• allowing warmer waters of the western Pacific to
migrate eastward and eventually reach the South
American Coast.
– The cool nutrient-rich sea water normally
found along the coast of Peru is replaced by
warmer water depleted of nutrients, resulting
in a dramatic reduction in marine fish and
plant life.
•
NOAA Image
and text
El Niño
El Niño
•
El Niño
NOAA Image
and text
La Niña-Related Rainfall Patterns
over the Tropical Pacific
•
NOAA Image
and text
2. Mean tropical Pacific rainfall, winds,
and subsurface ocean temperatures
•
La Niña-Related Winds, Walker Circulation,
and Subsurface Ocean Temperatures
NOAA Image
and text
La Niña-Related Global Temperature
and Precipitation Patterns
•
•
World Connections of weather patterns
shift in the distribution of heat in the
atmosphere and ocean which moves things
around (Boiling pot)
NOAA Image
and text
La Niña
NOAA Image
and text
•
NOAA Image
and text
•
NOAA Image
and text
Current Data
• Stronger easterly (coming from the east)
winds occur moving surface water away
from the western coast of South America.
• La Niña (female child)
• La Niña occurs roughly half as often as El
Niño.
Current La Niña
Sea Surface Temperatures
•
NOAA Image
and text
Upper ocean heat changes
•
NOAA Image
and text
Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
An el nino is characterized by a general warming of the water in the
central and eastern pacific.
Atmosphere forces the ocean by a weakening of the easterly trades
in the central and eastern pacific.
Atmosphere responds by shifting thunderstorm activity eastward to
the central pacific.
Implications: Interruption of fishery along western margins of
South America, failure and/or weakening of the Indian Monsoon
impacting agriculture in that region.
•
NOAA Image
and text
•
NOAA Image
and text
Ocean Anomalies
Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
El nino remote forcing: the modulation of the normal patterns in
the equatorial pacific influence weather patterns around the
world:
In the U.S., the pacific storm track is shifted southward leading
resulting in storminess over the southwestern U.S. and droughts
over the Pacific Northwest. Precipitation is often reduced over
the southeastern U.S.
Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
•
Natural variability can be classified by its forcing type (internal or
external to the climate system) and whether it is periodic/cyclic or
episodic.
Modes of Natural Variability that we know of:
timescale
1. Seasonal
90 days
2. El nino
3-5 yrs
3. North Atlantic Oscillation
decadal
4. Volcanism
none
5. Ice ages
40,000 yrs
6. Pacific Decadal
20-50 yrs
•
The negative NAO index phase
shows a weak subtropical high
and a weak Icelandic low.
•
The reduced pressure gradient
results in fewer and weaker winter
storms crossing on a more westeast pathway.
•
They bring moist air into the
Mediterranean and cold air to
northern Europe
•
The US east coast experiences
more cold air outbreaks and
hence snowy weather conditions.
Meteo 1020 – Lecture 4
The Natural Variability of the Earth-Atmosphere System
Natural variability can be classified by its forcing type (internal or
external to the climate system) and whether it is periodic/cyclic or
episodic.
Modes of Natural Variability that we know of:
timescale
1. Seasonal
90 days
2. El nino
3-5 yrs
3. North Atlantic Oscillation
decadal
4. Volcanism
none
5. Ice ages
40,000 yrs
6. Pacific Decadal
20-50 yrs
The NAO index is defined as the anomalous
difference between the polar low and the
subtropical high during the winter season
(December through March)
form forcing
cyclic external
cyclic internal
cyclic internal??
episodic external
cyclic internal
cyclic ????
The Negative NAO
•
North Atlantic Oscillation
•
form forcing
cyclic external
cyclic internal
cyclic internal??
episodic external
cyclic internal
cyclic ????
Positive NAO Index
•
The Positive NAO index phase
shows a stronger than usual
subtropical high pressure center
and a deeper than normal
Icelandic low.
•
The increased pressure
difference results in more and
stronger winter storms crossing
the Atlantic Ocean on a more
northerly track.
•
This results in warm and wet
winters in Europe and in cold
and dry winters in northern
Canada and Greenland
•
The eastern US experiences
mild and wet winter conditions
Volcanic eruptions and
climate:
•
The present atmospheric
composition, Nitrogen-78%,
Oxygen-21%, Argon-<1%,
water vapor-0.4%, carbon
dioxide-0.036%
•
How did the present
atmospheric composition
evolve?
•
Assume outgassing from early
volcanoes provided the first
atmosphere.
•
Composition of volcanic gasses:
Water vapor-80%, Nitrogen-1%,
Oxygen-0%, carbon dioxide12%, sulphur compounds and
others-7%
Volcanism and the early atmosphere:
So how did the atmosphere evolve from the volcanic composition to
our present composition?
Earth’s Atmosphere Develops
1. Water began to precipitate early – forming oceans
2. Carbon Dioxide dissolved rapidly in the early oceans reaching
saturation and leading to precipitate of Calcium carbonate to the
deep ocean
3. Nitrogen and argon built up slowly since it does not dissolve in sea
water
4. Oxygen built up in the atmosphere due to by product of
photosynthesis.
http://www.globalchange.umich.edu/globalchange1/current/lectures/first_
billion_years/first_billion_years.html
EFFECTS OF LARGE EXPLOSIVE TROPICAL
VOLCANOES ON WEATHER AND CLIMATE
Volcanoes produced the
atmosphere and the oceans
EFFECT/MECHANISM
Volcanic
emissions
1. Enhance or reduce El Niño?
BEGINS
DURATION
1-2 weeks 1-2 months
Tropospheric absorption of shortwave and longwave radiation, dynamics
N2
remains
N2
CO2
photosynthesis
O2
H2O
condensation
2. Reduction of diurnal cycle
Immediately 1-4 days
Blockage of shortwave and emission of longwave radiation
99% of
atmosphere
3. Summer cooling of NH tropics, subtropics Immediately 1-2 years
Blockage of shortwave radiation
4. Reduced tropical precipitation
Immediately
~1 year
Blockage of shortwave radiation, reduced evaporation
oceans
5. Reduced Sahel precipitation (?)
1-3 months 1-2 years
Blockage of shortwave radiation, reduced land temp., reduced evaporation
Tambora in 1815, together with an eruption
from an unknown volcano in 1809, produced
the “Year Without a Summer” (1816)
EFFECTS OF LARGE EXPLOSIVE TROPICAL
VOLCANOES ON WEATHER AND CLIMATE
EFFECT/MECHANISM
BEGINS
6. Ozone depletion, enhanced UV
DURATION
1 day
1-2 years
Dilution, heterogeneous chemistry on aerosols
7. Global cooling
Blockage of shortwave radiation
Immediately 1-3 years
multiple eruptions: 10-100 years
8. Stratospheric warming
Immediately 1-2 years
Stratospheric absorption of shortwave and longwave radiation
9. Winter warming of NH continents
½-1½ years 1 or 2 winters
Stratospheric absorption of shortwave and longwave radiation, dynamics
High latitude eruptions:
10. Cooling of continents
Immediately 1-2 years
Blockage of shortwave radiation
11. Reduction of Indian summer monsoon ½-1½ years 1 or 2 summers
Continental cooling, reduction of land-sea temperature contrast
Tambora, 1815, produced the
“Year Without a Summer” (1816)
“The Scream”
Edvard Munch
Percy Bysshe Shelley
Mary Shelley
George Gordon,
Lord Byron
Painted in 1893
based on Munch’s
memory of the
brilliant sunsets
following the
1883 Krakatau
eruption.
These two photos show the Earth’s
limb at sunset before and after the
Mt. Pinatubo eruption. The first view
(STS41D-32-14) shows a relatively
clear atmosphere, taken August 30,
1984. Astronauts were looking at the
profiles of high thunderstorms topping
out at the tropopause at sunset;
different atmospheric layers
absorbed the last rays of light from
the sun as the spacecraft moved
eastward.
Pinatubo
June 12, 1991
Three days
before major
eruption of
June 15, 1991
The same type of photograph
(STS043-22-23) was taken August 8,
1991, less than two months after the
Pinatubo eruption. Two dark layers of
aerosols make distinct boundaries in
the atmosphere. The estimated
altitude of aerosol layers in this view
is 20 to 25 km.
Photo from USGS.
From http://earthobservatory.nasa.gov/Study/AstronautPinatubo/astronaut_pinatubo2.html
Casadevall et al. (1996)
After Pinatubo, Clark Air Force Base
25 km from volcano
Bataan
Photo by R. P. Hoblitt, June 15, 1991
After Pinatubo, Cubi Point Naval Air
Station, 40 km from volcano
After Pinatubo, Subic Bay Naval Base
35 km from volcano
Photo by Tom Grzelak
U.S. Navy photograph by R. L. Rieger
The climate effects of volcanic eruptions:
What makes an eruption climatically significant?
•
nature of the eruption – lava vs. ash (ash is more significant)
•
composition – need high sulfur dioxide gas content
•
location – Tropical eruption spread globally
In most eruptions, the particulates have only a minor effect. If the
sulfur dioxide gas can reach the stratosphere, it converts to small
sulfuric acid droplets that have long residence times in the stable
stratosphere. It is this cloud of particles that spread and influence
climate over long periods.
Note Figure 4.3 in the book.
Pacific Decadal Oscillation
•
Natural variability can be classified by its forcing type (internal or
external to the climate system) and whether it is periodic/cyclic or
episodic.
Modes of Natural Variability that we know of:
timescale
1. Seasonal
90 days
2. El nino
3-5 yrs
3. North Atlantic Oscillation
decadal
4. Volcanism
none
5. Ice ages
40,000 yrs
6. Pacific Decadal
20-50 yrs
form forcing
cyclic external
cyclic internal
cyclic internal??
episodic external
cyclic internal
cyclic ????
Pacific Decadal Oscillation
warm phase
phase
cool
http://teacherresourceexchange.org/science/coriolis/index.php
http://teacherresourceexchange.org/science/coriolis/index.php
How does weather move the
energy (heat) move from equator
to the poles?
Vertical winds, horizontal winds,
and the release of latent heat
transport the energy!
Our
atmosphere is a three cell model.
http://teacherresourceexchange.org/science/coriolis/index.php
These three cells transport energy to the poles.
Winds Patterns
Balance of 3 forces
1. The pressure gradient force causes wind
to blow from high pressure toward low
pressure.
2. The coriolis force causes wind to be
deflected to the right of the motion in the
northern hemisphere.
3. Friction which slows the wind.
Pressure Force
• More air on the left
hand side (higher
pressure).
• The pressure
difference over that
distance of the
sheet (the pressure
gradient force),
pushes the sheet to
the right.
Pressure Force
Pressure Gradient Force
• More air on the left
hand side (higher
pressure).
• The pressure
difference on either
side of the parcel
(the pressure
gradient force),
pushes the parcel to
the right.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/pgf.rxml
Pressure Gradient Force
Pressure Gradient Force
• Hurricane’s have a
strong pressure
gradient force!
• This generates fast
winds!
Winds Patterns are a
balance of 3 forces
Ifhttp://teacherresourceexchange.org/science/coriolis/index.php
the earth was not spinning,
air would move directly from high
to low pressure areas.
1. The pressure gradient force causes wind
to blow from high pressure toward low
pressure.
2. The coriolis force causes wind to be
deflected to the right of the motion in the
northern hemisphere.
3. Friction which slows the wind.
Coriolis Force
• Stronger as you move
AWAY from the
equator (dependant on
latitude).
• There must be initial
motion for the coriolis
to take place (there
must be a wind).
• Reference information:
Coriolis force = 2 * the
rotation rate of the
earth * sin (degree
latitude) * velocity of
the wind
Coriolis Force
Southern hemisphere
video (earth spinning
from the point of view
“underneath” the earth.
Video
Coriolis
Coriolis
(Northern Hemisphere- air moves to the right of
the initial motion)
(Northern Hemisphere- air moves to the right of
the initial motion)
Direction of initial motion
• Highs – clockwise rotation
• Lows – counterclockwise rotation
(cyclonic)
• Northern Hemisphere Surface map
• Northern Hemisphere Satellite map
Coriolis
Coriolis
(Southern Hemisphere - Air moves to the left of the
initial motion)
(Southern Hemisphere - Air moves to the left of the
initial motion)
• Highs- counterclockwise rotation
• Lows- clockwise rotation
Direction of initial motion
• Southern Hemisphere Satellite
• Southern Hemisphere Pressure
Coriolis
(earth turns underneath the slower wind)
Direction of initial motion
http://teacherresourceexchange.org/science/coriolis/index.php
Geostrophic Balance
• Coriolis Pressure Gradient Movement
Animation
Geostrophic Wind
Pressure Gradient Force = Coriolis Force
H
L
Initial
Motion
• Balance of forces
summary
• Pressure
• Coriolis
• Friction
Winds Patterns are a
balance of 3 forces
Geostrophic
Balance
Lines of constant pressure
Arrows show wind flow
Frictional Force
1. The pressure gradient force causes wind
to blow from high pressure toward low
pressure.
2. The coriolis force causes wind to be
deflected to the right of the motion in the
northern hemisphere.
3. Friction which slows the wind.
Pressure Gradient and Coriolis
and Friction
H
L
Initial
Motion
http://teacherresourceexchange.org/science/coriolis/index.php