1. Global annual cycle F Kucharski Fred Kucharski, Abdus Salam ICTP, Earth System Physics Section, Climate Variability Group, Trieste, Italy

2. http://www.windows2universe.org/earth/climate/cli_seasons.html

4. External forcing Longitude average of Solar surface radiation In W/m^2 This clearly drives our seasons

5. Of course, this translates Into seasonal variations of surface temperature (here in degrees C) However, note that the north- south excursions are much smaller……..and there is a 1-2 month shift -> Inertia of Oceans

6. May be a more interesting field: Sea-level pressure (shown here in hPa) As you know, it rains where the pressure is low…

7. But first have a look At the consequences For the zonal mean Winds [m/s]. Trades Interesting interruptions of trades: Monsoons! Extratropical westerlies

8. And finally precipitation: The extratropical rainbelts The tropical ITCZ (precip in mm/day)

9. Diff temp djf-jja Cool, why?

10. Even the global men surface temperature has a seasonal cycle (due to heat capacity differences between ocean and land)

11. Diff slp djf-jja Mediterranian Climates Subtropical monsoons

12. Mediterranian Climates Subtropical monsoons Diff prec djf-jja

13. Picture can be quite different if we zoom into specific regions: Indian Monsoon

14. Seasonality of Indian Monsoon

15. Mechanism 2 : Different heat capacity of land and sea (land-sea breeze)

17. Zoom into Mediterranean

18. Surface pressure: Azores high moving northwards

19. Zoom into the Mediterranean

20. Also Carbon Dioxide has a seasonal Cycle……..

22. SUMMARY The annual cycle is the largest climate variation on Earth. It is forced by the Earth axis tilt with respect to the rotation axis around the sun. The surface temperature reacts to this forcing with some delay, depending on the total heat capacity (land/ocean). The responses of other climatic fields, such as surface pressure, winds and rainfall, is also very clear, but more complicated. Usually the annual cycle is stronger in high latitudes than in low latitudes, particularly for temperature. The climate in the mediterranean region is strongly influenced by the seasonal cycle, but also the climate in monsoon regions (i.e. Indian Monsoon).

23. THANK YOU!