1. Activities at GKSS related to D&A problems Hans von Storch Institute for Coastal Research GKSS Research Centre Geesthacht, Germany INTERESTED IN WIND OVER SEA

2. Overview Millennial forced runs "Erik the Red" and "Christof Columbus" 1958-2000 regional downscaling/reconstruction Changes storminess / WASA Ocean waves and detection for (erosion relevant) wave energy change.

3. 1550-2000 simulation Changing solar forcing and time variable volcanic aerosol load; greenhouse gases 1550-2000 simulation Changing solar forcing and time variable volcanic aerosol load; greenhouse gases Forced Simulation

4. Climate model used Atmosphere: ECHAM4 horizontal resolution T30 ~ 300 km at mid latitudes Ocean: HOPE-G horizontal resolution T42 ~ 200 km at mid latitudes increased resolution in the tropics Model provided as community climate by Model & Data Group at MPI for Meteorology and run at German Climate Computing Centre (DKRZ) and computing facilities at FZ Jülich Institut für Küstenforschung I f K

5. More actual data via internetinternet Control 1990 equilibrium Erik the Red Christoph Columbus

6. Information provided by Fidel González-Rouco and Simon Tett HadCM3 ECHO-G differences relative to the 1550-1800 average and are a 25-year running average.

7. control forced Institut für Küstenforschung I f K

8. 1958-2000 regional downscaling/reconstruction Spectral nudging Dutch coast extremes (maps) K13 extremes wind & waves (return values)

9. Institut für Küstenforschung I f K Concept of Dynamical Downscaling RCM Physiographic detail 3-d vector of state Known large scale state projection of full state on large-scale scale Large-scale (spectral) nudging

10. Institut für Küstenforschung I f K Skill in representing marine winds Red: buoy, yellow: radar, blue: wave model run with REMO winds wave direction significant wave height [days]

11. Extreme wind speeds 20-year return values of wind speed, based on daily 1992-97 data (color codes) plus from station data in NL (numbers in black) Southern North Sea DWDREMO Feser, pers. comm.

12. Institut für Küstenforschung I f K Weisse, pers. comm. Extreme value analysis of significant wave height at platform K13 (southern North Sea) January 1980-January 1997 simulatedobserved Skill in representing marine winds 2 5 10 25 years [m]

13. Changing storminess / WASA Geostrophic wind + pressure tendencies Ekofisk SMHI scenario

14. Trends in storminess Alexandersson, SMHI, 2003 intra-annual 99% quantiles of geostrophic wind, averaged over many triangles. North Sea Baltic Sea

15. Bärring, 2003

16. red: local observations solid: RCM reconstruction (downscaling NCEP) + WAM dashed: WASA estimate + WAM Weisse, pers. comm. 99% 95% 90% 50% 99% 95% 90% 50% Wind speed Significant wave height

17. Scenario for changed wind conditions in the wider North Sea area, end of 21st century (A2) Rossby Center, Norrköping, Sweden Mean wind speed Storm wind speeds m/sec

18. ABSTRACT: In the central North Sea we have observed an increase in the frequency of eastwardly propagating waves in the last 4 decades. To assess the significance of this change, wave statistics for the 20th century were reconstructed with a statistical model. With a linear multivariate technique (redundancy analysis), monthly mean air pressure fields over the North Atlantic and Western Europe were downscaled on the intramonthly frequency of directional wave propagation. When compared against this reference, the recent change appears statistically significant at the 5% level. In order to investigate the reason for this local climatic change, the reconstruction was compared with the downscaled results of control and transient GCM scenarios (ECHAM4-OPYC3) and with the results obtained in a high-resolution time-slice experiment with increased concentrations of greenhouse gases and aerosols. Both estimates are qualitatively consistent with the changes observed in the last 4 decades. We suggest that the recent increase in eastward propagation is a local manifestation of anthropogenic global climate change. Anthropogenic climate change shown by local wave conditions in the North Sea (Arnt Pfizenmayer, Hans von Storch)

19. Comparison of the 30 yr running mean of the monthly frequency of eastwardly propagating waves (3 h time steps, anomalies). The reconstruction of the 20th century (black line), the transient T42 run (dotted line), the T42 control run (grey line) and the time-slice experiment T106 (star) are shown. Dashed lines are the estimated 5, 95 and 99% confidence intervals. Pfizenmayer and von Storch, 2002

20. Pfizenmayer, 2002