page 1. page 2 german presentations colijn franciscus, gkss: cosyna von storch jin-song, mpim: wind...
TRANSCRIPT
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German presentations• COLIJN Franciscus, GKSS: COSYNA• VON STORCH Jin-Song, MPIM: Wind generated power
input into the deep ocean • VON STORCH Hans, GKSS: Downscaling Tropical
Cyclones from global re-analysis: Statistics of multi-decadal variability of TC activity in E Asia, 1948-2007
• STANEV Emil, GKSS: A step towards model supported monitoring of the German Bight
• MEYER Bernhard, Uni HH: Suspended matter modelling• POHLMANN Thomas, Uni HH: Application of the
circulation model “HAMSOM” to Asian waters
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Downscaling Tropical Cyclones from global re-analysis:
Statistics of multi-decadal variability of TC activity in E
Asia, 1948-2007 VON STORCH Hans and FESER Frauke
1Institute for Coastal Research, GKSS Research Center, Germany
2clisap-Klimacampus, University of Hamburg, Germany
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• Any assessment of how weather patterns have changed in recent decades requires long and homogeneous time series.
• Local time series representing wind speeds are usually not homogeneous, even for a few decades (sensitivity to instrumentation and surrounding).
• Homogeneous description of variability of meso-scale storms in recent decades has also not been achieved.
• Model-based “reconstructions” may help
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Analysis using additional aircraft reports.
Analysis using all available surface observations
Max: 52 m/s
Max: 20 m/s
Example: Inhomogeneity of analyses of hurricanes – Erin, in September 2001
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Dynamical downscaling, deriving regionally disaggregated descriptions from global re-analysis or global climate change scenarios.
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Problem for synoptic systems solved by CoastDat@GKSS in N Europe, using RCM spectrally nudged to NCEP
- retrospective analysis 1958-2007- 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
Wind speed [m/s] Wind direction [degrees]
Sig. wave height [m] Mean wave direction [degrees]
(Weisse and Günther. 2007)
Observations – black; Hindcast - green
At a platform in the S North Sea
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• We have implemented the dynamical downscaling approach for E Asian marine weather.
• The key question is – will we master the description of typhoons?
• Done: Case studies and seasons – formation of typhoons induced by large scale dynamics and NOT by initial values.
• Presently under examination: Continuous 6-decade simulations constrained by NCEP global re-analyses.
Feser, F., and H. von Storch, 2008: Regional modelling of the western Pacific typhoon season 2004, Meteor. Z. 17 (3), 1-10. DOI: 10.1127/0941-2948/2008/0282Feser, F., and H. von Storch, 2008: A dynamical downscaling case study for typhoons in SE Asia using a regional climate model. Mon. Wea. Rev. 136, 1806-1815
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Case study: Typhoon Winnie, August 1997 simulated with different
set-ups
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12 TCs in Seaso
n 2004only 10
were found in
CLM simulationFollowing Zhang et
al., 2007. Meteor. Atmos. Phys.
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Simulated typhoons are weaker than found in the „best track data“ – too high core pressures, too weak winds,But considerably stronger than in the driving NCEP re-analyses.
The model‘s performance does not improve much by enhancing the horizontal resolution from about 50 km to about 16 km.
Experiments with different convection parametrizations will be done in the future.
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Complete simulation of 1948-2007 using CLM with 0.5º grid resolution and NCEP/NCAR reanalysis
Spectral nudging of scales larger than about 800 km.
All „best tracks“, 1951-2007
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1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
0
10
20
30
40
E A sian t r opical cyclones as given byC LM dow nscaling
JM A best track data
Note: different criteria employed
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36 “best tracks26 tracks in CLM
16 “best tracks” 16 tracks in CLM
Interannual variability
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1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
15
20
25
30
35
40
Annual number o f T Cs dow nscaled
linear fit
11-year running m ean
best track
linear fit
11 year running m ean
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Annual statistics of minimum pressure along tracks
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Findings so far:
1)CLM-simulated typhoons too weak.2)Number and interannual variability in CLM similar to „best track“ data set.3)Long term trends in CLM and in in „best track“ markedly different.4)In CLM, intensification since about 1980.5)In „best track“, weakening since about 1980.
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Typhoon 195313 (TESS)
1953-09-18 00:00 1953-09-27 18:00
Largest drop in BT core pressure:
93 hPa in 6 hours
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The CLM shows much smaller drops in core pressure- probably too small in most cases.
The most extreme pressure falls described in the “best track” data set took place over the open ocean, where no satellite data was available in 1953 – how was it observed?
Later years show overall less extreme pressure 6-hourly drops.
Use caution when using earlier “best track” years.
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Overall ConclusionsDynamical Downscaling of NCEP
reanalysis with regional climate models returns typhoon climatology better than NCEP, even if cyclones are still too weak.
Results concerning change- Strong year-to-year variability- Little decadal variability- No overall trend in numbers- Trends in intensities opposite in CLM
and in “best track”.- “Best track” suffer likely from severe
inhomogeneities in the early years (e.g., 1953)