1. 夏兰 Lan Xia (Yunnan University) Hans von Storch and Frauke Feser (Institute of Coastal Research, Helmholtz Ceter Geesthacht: Germany) A comparison of quasi-millennial extratropical winter cyclone activity between the Northern and Southern Hemisphere

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

3. Data and method Data from 1000-1990 “Erik-the red” run with the global climate model ECHO-G exposed to estimated volcanic, solar and GHG forcing. Horizontal resolution is T30 (ca. 3.75°) for the atmosphere. The output is every 12 hourly data. 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.  Cyclone numbers are stable with small variability and decoupled 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

7. 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

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 Indian Ocean South Pacific

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)  Geometric positions of cyclone tracks differ very little NH

12. 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

13. 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

14. 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

15. Conclusions There is very strong year-to-year variability for winter extratropical cyclone numbers of both hemispheres. Northern Hemisphere midlatitude winter storm tracks are mostly stationary at the centennial time scales. This stationarity is also valid for the track locations indicating only minor changes. The mean tracks of clusters over the Southern Indian Ocean and near New Zealand shift poleward from the 11 th to the 20 th century. The frequency of storm tracks for Pacific/Atlantic clusters is linearly related to the mean circulation like the Aleutian Low, the NAO or the Antarctic Oscillation (AAO) pattern.

16. Related Papers (1) Lan Xia, Hans von Storch, Frauke Feser, and Jian Wu, A study of quasi-millennial extratropical winter cyclone activity over the Southern Hemisphere. Climate Dynamics, 2015, Doi: 10.1007/s00382-015-2954-x. (2) Lan Xia, Hans von Storch, and Frauke Feser, Quasi-stationarity of centennial Northern Hemisphere midlatitude winter storm tracks. Climate Dynamics, 2013, 41: 901-916.