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

Downscaling cascade Globale development (NCEP) Dynamical Downscaling Simulation with barotropic model of North Sea Dynamical (process based models) cascade for constructing variable regional marine weather statistics, processing NCEP/NCAR large-scale analysis of 1948/ weather Dynamical Downscaling

60 year construction available for N Europe from using RCM spectrally nudged to NCEP - retrospective analysis 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 and comparison with observations. J. Climate 18,

Oct Polar Lows

Comparison with satellite data Count of Polar Lows per month. – downscaling - satellite data (Blechschmidt, 2008) Polar Lows

Downscaling re-analysis Number of polar lows Polar Lows

Downscaling scenarios Polar Lows

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)

RCM simulations 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 All tracks in “reconstruction” SE Asian Typhoons

Note: different criteria employed SE Asian Typhoons

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 )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”)