Download Polar Lows - Hans von Storch

Institute for Coastal Research
of GKSS Research Center
Germany
Changing statistics of polar
lows and typhoons in the past
and foreseeable future.
Hans von Storch, Frauke Feser,
Matthias Zahn, Monika Barcikowska,
Chen Fei and Xia Lan
Overview:
a) Dynamical downscaling strategy developed
for NE Atlantic to obtain homogeneous
analysis of past and present change as well
as scnearios of possible future conditions
a) Application of downscaling strategy to
Polar Lows in the N Atlantic
b) Application of down scaling strategy to SE
Asian typhoons
Dynamical
Downscaling
Dynamical (process based
models) cascade for constructing
variable regional marine weather
statistics, processing
NCEP/NCAR large-scale analysis
of 1948/58-2008 weather
Globale development
(NCEP)
Simulation with barotropic
model of North Sea
Dynamical Downscaling
Downscaling cascade
60 year construction available for N Europe from
CoastDat@GKSS, using RCM spectrally nudged to NCEP
- retrospective analysis 1958-2005
- good skill with respect
to statistics, but not all
details are recovered.
Weisse, R., H. von Storch and F. Feser, 2005: Northeast Atlantic and North Sea storminess as simulated by a
regional climate model 1958-2001 and comparison with observations. J. Climate 18, 465-479
Polar Lows
Oct
Polar Lows
Count of Polar Lows
per month.
– downscaling
- satellite data
(Blechschmidt, 2008)
Comparison with satellite data
Polar Lows
Number of polar lows
Downscaling re-analysis
Polar Lows
Downscaling scenarios
SE Asian Typhoons
Analysis by best track data inhomogeneous and contradictory
(cf. Ren, F., Liang, J., Wu, G., Dong,W. and X. Yang, 2010: Reliability Analysis of
Climate Change of Tropical Cyclone Activity in the Northwest Pacific. J. Climate)
• CCLM regional
atmospheric model
• 50 km grid resolution
• “Reconstructions” –
NCEP forcing, incl.
spectral nudging (800
km), 1948-today
• “Scenario” –
ECHAM5/MPIOM
A1B1; also spectral
nudging
SE Asian Typhoons
All tracks in “reconstruction”
RCM simulations
SE Asian Typhoons
50
Number of detected typhoons
JMA Best Track
CCLM "normal"
CCLM "high"
40
30
20
10
1950
1960
1970
1980
Note: different criteria employed
1990
2000
2010
SE Asian Typhoons
50
Number of detected typhoons
Scenario A1B
CCLM "normal"
40
30
20
10
1950
1960
1970
1980
1990
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100
SE Asian Typhoons
Maximum typhoon wind speed
in CCLM simulations
plus linear trends
Reconstruction "normal"
Scenario A1B
50
Line/Symbol Plot 18
Fit 1: Linear
m/s
40
30
20
1950
1960
1970
1980
1990
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100
Reconstruction findings:
1) Regional climate model CCLM simulates polar lows and
typhoons.
2) Number and interannual variability in CLM similar to „best
track“ data set and to limited satellite data evidence.
3) Simulated typhoons and polar lows too weak.
Polar Lows: No multi-decadal reference available.
Typhoons
1) Long term trends in CCLM and in „best track“ markedly
different.
2) In CCLM, some intensification mainly since about 1980.
3) In JMA-„best track“, mainly weakening since about 1980.
Scenario findings:
Polar Lows: Number decreases, pattern shifts poleward.
Typhoons: Number and intensity in scenario A1B slightly
decreasing, while intensity almost stationary. Note – only
one scenario.
Scenarios not (very) consistent with reconstructions
1. Polar lows: reconstructions: no change, scenario: less
storms)
2. Typhoons: reconstructions: increase in number, but
decrease in scenario)
Conclusions
• Dynamical downscaling re-analyses or climate
change scenarios a useful approach.
• “Continuity” of past change and of expected
future change a significant issue (in the
framework of “detection and attribution”)