General Circulation and Climate Zones

1. General Circulation and Climate Zones Martin Visbeck DEES, Lamont-Doherty Earth Observatory visbeck@ldeo.columbia.edu

2. Outline • Introduction- Climate zones • The surface wind circulation - Climate Belts • The sea level pressure distribution - Monsoons • The upper troposphere • The subtropical jet stream (thermal wind relation) • The Hadley circulation • Middle latitude weather systems (baroclinic instability) • Climate zones and rainfall

3. General Circulationtake away ideas and understanding • Understand how the global atmospheric circulation relates to the distribution of solar heating over the globe. • Learn about the components of the global circulation: • the mean meridional circulation, • trade winds and westerlies, • jet streams and weather belts. • Note the effect of mountains and land-ocean distribution on the global circulation. • Learn about climate zones and the global distribution of temperature and rainfall.

4. Climate Zones • Moist Tropical Climate • Dry Climate • Moist Climate & Mild Winters • Moist Climate & Severe Winters • Polar Climate • Highland Climate

5. Climate Zones • Moist Tropical Climate • Dry Climate • Moist Climate & Mild Winters • Moist Climate & Severe Winters • Polar Climate • Highland Climate

6. Climate Zones • Moist Tropical Climate • Dry Climate • Moist Climate & Mild Winters • Moist Climate & Severe Winters • Polar Climate • Highland Climate

7. Climate Zones • Moist Tropical Climate • Dry Climate • Moist Climate & Mild Winters • Moist Climate & Severe Winters • Polar Climate • Highland Climate

8. Climate Zones • Moist Tropical Climate • Dry Climate • Moist Climate & Mild Winters • Moist Climate & Severe Winters • Polar Climate • Highland Climate

9. Climate Zones • Moist Tropical Climate • Dry Climate • Moist Climate & Mild Winters • Moist Climate & Severe Winters • Polar Climate • Highland Climate

10. General CirculationThe surface wind circulation - climate belts • Hurricanes "move"to the west.... why?

11. General CirculationThe surface wind circulation - climate belts • Weather systems "move"to the east.... why?

12. General CirculationThe surface Temperature Surface air temperature: Warm Equator, cold Polar regions Is this in radiative balance?

13. General CirculationThe surface wind circulation - climate belts • Atmospheric motion is driven by the uneven horizontal distribution of pressure and thus net incoming radiation. On a global scale, the most outstanding part of this uneven distribution is its latitudinal dependence.

14. General CirculationThe surface energy balance Atmosphere/Ocean Heat Transport I ~ sT4

15. General CirculationThe surface wind circulation - climate belts • As we have discussed earlier, atmospheric motion is driven by the uneven horizontal distribution of net incoming radiation. On a global scale, the most outstanding part of this uneven distribution is its latitudinal dependence. • The atmosphere (and oceans) respond to this imbalance by attempting to move heat from the tropics and subtropics, where insolation surpasses the infrared terrestrial radiation going out to space, to the middle and high latitudes, where there is a net radiative loss of heat. Convection, the vertical process of heat transport, and advection, the horizontal process of heat and moisture transport, work together to accomplish this goal.

16. General CirculationThe surface energy balance How is the planet transporting this heat from the equator to the pole? Atmosphere/Ocean Heat Transport

17. General CirculationLarge scale energy transport A non rotating planet might have a circulation like this. What will the Coriolis force do?

18. General CirculationThe large scale wind system A slow rotating planet might have a circulation like this. What will the Coriolis force do?

19. General CirculationThe surface energy balance What will the Coriolis force do? A three cell structure emerges: Hadley Cell Mid-L. Cell Polar Cell

20. General CirculationThe surface wind and pressure Why is there a High at the "Horse Latitudes" at about 30° latitude?

21. General CirculationThe tropical circulation Convection in the ITCZ Sinking near 30 N/S causes the high pressure

22. General CirculationThe surface wind and pressure Why is there a Low at about 60° latitude? Polar Cell

23. General CirculationThe surface wind and pressure Given the High / Low pressure distribution what would a frictional balance look like?

24. General CirculationThe surface wind and pressure Given the High / Low pressure distribution what would a geostrophic balance look like?

25. General CirculationThe surface wind and pressure • Polar Easterlies • Westerlies • Trade Winds • ITCZ (Low) • Subtropical High • Subpolar Low

26. General CirculationThe surface pressure • NorthernWinter (January) • High over Land, Low over Ocean

27. General CirculationThe surface pressure • Northern Summer (July) • High over Ocean, Low over Land

28. Monsoon • Seasonal cycle of heating produces the monsoon winds akin to the daily occurring sea-breeze.

29. General CirculationThe surface wind and pressure Lets look at the upper level flow... 500 and 300 hPa level.

30. General CirculationAtmospheric Heat transport • Two direct cellsHadley & Polar • One indirect cellMid-Latitude (storms)

31. Poleward Heat Transport by Weather Systems

32. General CirculationThe seasonal cycle revisited • Strong Temperature contrast in high latitudes • Strong over Land...why?

33. General CirculationClimate Zones What will the Coriolis force do? A three cell structure emerges: Hadley Cell Mid-L. Cell Polar Cell

34. General CirculationClimate Zones Evaporation - Precipitation Evaporation: where air is subsiding Precipitation: where air is rising

35. Climate Zones • Moist Tropical Climate • Dry Climate • Moist Climate & Mild Winters • Moist Climate & Severe Winters • Polar Climate • Highland Climate