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Download Polar Lows - Hans von Storch
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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”)