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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

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German presentations

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  1. 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 German presentations

  2. 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

  3. 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

  4. Example: Inhomogeneity of analyses of hurricanes – Erin, in September 2001 Analysis using additional aircraft reports. Analysis using all available surface observations Max: 20 m/s Max: 52 m/s

  5. Dynamical downscaling, deriving regionally disaggregated descriptions from global re-analysis or global climate change scenarios.

  6. Wind speed [m/s] Wind direction [degrees] Sig. wave height [m] Mean wave direction [degrees] • Problem for synoptic systems solvedby 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. Observations – black; Hindcast - green At a platform in the S North Sea (Weisse and Günther. 2007) 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

  7. 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: 10.1127/0941-2948/2008/0282 Feser, 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

  8. Case study: Typhoon Winnie, August 1997 simulated with different set-ups

  9. 12 TCs in Season 2004 only 10 were found in CLM simulation Following Zhang et al., 2007. Meteor. Atmos. Phys.

  10. 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.

  11. 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

  12. Note: different criteria employed

  13. Interannual variability 16 “best tracks” 16 tracks in CLM 36 “best tracks26 tracks in CLM

  14. Annual statistics of minimum pressure along tracks

  15. Findings so far: • CLM-simulated typhoons too weak. • Number and interannual variability in CLM similar to „best track“ data set. • Long term trends in CLM and in in „best track“ markedly different. • In CLM, intensification since about 1980. • In „best track“, weakening since about 1980.

  16. Typhoon 195313 (TESS) 1953-09-18 00:00 1953-09-27 18:00 Largest drop in BT core pressure: 93 hPa in 6 hours

  17. 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.

  18. Overall Conclusions • Dynamical Downscaling of NCEP reanalysis with regional climate models returns typhoon climatology better than NCEP, even if cyclones are still too weak. • Resultsconcerningchange • 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)

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