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Annual- and zonal-mean climate of the tropics (NCEP)

Annual- and zonal-mean climate of the tropics (NCEP). Relative humidity [%]. Temperature [degC]. subtropical high. subtropical high. surface pressure [mb]. equatorial trough. Angular momentum conservation and zonal acceleration. When parcel moves poleward, r decreases

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Annual- and zonal-mean climate of the tropics (NCEP)

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

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

  3. Walker cell

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

  5. Monsoon circulation

  6. Asian monsoon

  7. American monsoons N. America S. America

  8. African monsoon

  9. Moist static energy h (105 J/kg) DJF JJA

  10. Components of moist static energy averaged over Hadley cell (10S–30N, DJF) total potential pressure (hPa) sensible latent energy (105 J/kg)

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

  12. Net surface energy flux (NCEP, W/m2)

  13. 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”)

  14. Tropical cyclone tracks, 1985–2005

  15. Distribution of cyclone occurrence by intensity

  16. Tropical cyclone structure

  17. Tropical cyclone structure

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

  19. Potential intensity as function of Ts, T0

  20. Potential intensity compared with actual intensity

  21. 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.

  22. Cold wakes

  23. Increasing destructiveness Power Dissipation Index:

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