1. Lan Xia (Yunnan University) cooperate with Prof. Hans von Storch and Dr. Frauke Feser A study of Quasi-millennial Extratropical Cyclone Activity using Tracking and Clustering Methods

2. Many studies deal with recent decades or only last century. Quasi-millennial variability of global extratropical storms in winter is studied through tracking and clustering method. Motivation Gulev et al. 2001 UK Christmas Eve storm

3. Data and method Simulation data from 1000-1990 run with the global climate model ECHO-G combined with ECHAM4 and HOPE-G (Min et al. 2005). Horizontal resolution is T30 (ca. 3.75°) for the atmosphere. The output is every 12 hourly data. It has been used for studying midlatitude baroclinic cyclones (Fischer-Bruns et al. 2005). An automatic tracking algorithm developed by Hodges (1994, 1995, and 1999) is applied.

4. Comparison of cyclone density NCEP Difference  Cyclone statistics from ECHO-G are realistic 40 years mean cyclone density (cyclone numbers per winter per 218000 km 2)

5. Changes of cyclone numbers and temperature track numbers surface air temperature (SAT) Time series of winter (DJF) extratropical cyclone numbers (black) and surface air temperature (red) in the NH from year 1001-1990 NH

6. Changes of cyclone numbers and temperature track numbers surface air temperature (SAT) Time series of winter (DJF) extratropical cyclone numbers (black) and surface air temperature (red) in the SH from year 1001-1990 SH

7.  Cyclone numbers are stable with small variability and decouple from temperature variations (Fischer-Bruns et al. 2005). Changes of cyclone numbers and temperature track numbers surface air temperature (SAT) Average annual winter cyclone numbers and SAT for different centuries NH

8. Changes of cyclone numbers and temperature track numbers surface air temperature (SAT) Average annual winter cyclone numbers and SAT for different centuries SH

9. Clustering results North Pacific North Atlantic  Clusters are consistent with cyclone genesis areas

10. Clustering results 11 th century 20 th century Mean tracks of ten clusters for the NH in the 11 th century (red) and 20 th century (blue)  Geometric positions of cyclone tracks differ very little NH

11. Clustering results 11 th century 20 th century Mean tracks of ten clusters for the NH in the 11 th century (red) and 20 th century (blue)  Cluster 1,2,3 and 10 move northward  Cluster 9 moves southward SH

12. Second pattern: r=0.39 represents 35% of variance Canonical Correlation Analysis (CCA) patterns for North Pacific First pattern: r=0.59 represents 48% of variance

13. First pattern: r=0.51 represents 39% of variance Canonical Correlation Analysis (CCA) patterns for North Atlantic Second pattern: r=0.27 represents 31% of variance

14. Conclusions Quasi-stationarity is shown for Northern Hemisphere midlatitude winter storm tracks at the centennial time scales. This stationarity is also valid for the track locations indicating only minor changes. The frequency of storm tracks for Pacific/Atlantic clusters is linearly related to mean circulation various like the Aleutian Low and the North Atlantic Oscillation (NAO) pattern.

15. Thank you very much for your attention!