1. Annual- and zonal-mean climate of the tropics (NCEP) Relative humidity [%] Temperature [degC] surface pressure [mb] equatorial trough subtropical high subtropical high

3. Angular momentum conservation and zonal acceleration When parcel moves poleward, r decreases so v must increase in order to keep L constant

4. Walker cell

5. The real Walker cell (Trenberth et al. 2000)

6. Monsoon circulation

7. Asian monsoon

8. American monsoons N. AmericaS. America

9. African monsoon

10. Moist static energy h (10 5 J/kg) DJF JJA

11. Components of moist static energy averaged over Hadley cell (10S–30N, DJF) pressure (hPa) energy (10 5 J/kg) latent potential sensible total

12. Vertically averaged energy transport (arrows) and its divergence (shade, W/m2) (Trenberth&Stepaniak 2003) Total Dry Moist

13. Net surface energy flux (NCEP, W/m 2)

14. Tropical cyclones Definition: cyclonic system driven principally by energy transfer from ocean. Categories by max surface wind: –up to 17 m/s: tropical depression –18–32 m/s: tropical storm –over 32 m/s: hurricane/typhoon Scale: 100–1000 km diameter Frequency: ~ 80 tropical cyclones per year globally (very stable number) Occur mostly in summer/early autumn Hurricane-like storms also occur in Mediterranean (“medicanes”) and in Arctic (“polar lows”)

15. Tropical cyclone tracks, 1985–2005

16. Distribution of cyclone occurrence by intensity

17. Tropical cyclone structure

19. Potential intensity theory W = rate of working by cyclone D = energy dissipation rate V max = max surface wind speed p(V max ) = surface pressure at location of V max

20. Potential intensity as function of Ts, T0

21. Potential intensity compared with actual intensity

22. Winds here are normalized by the maximum potential value. Note that this is a cumulative distribution, ie. the y-axis gives the probability of achieving a windspeed equal or greater than the corresponding x-axis value.

23. Cold wakes

24. Increasing destructiveness Power Dissipation Index: