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Geosciences LibreTexts

11.14: Review

  • Page ID
    10215
  • The combination of solar radiation input and IR output from Earth causes polar cooling and tropical heating. In response, a global circulation develops due to buoyancy, pressure, and geostrophic effects, which transports heat from the tropics toward the polar regions, and which counteracts the radiative differential heating. 

    Near the equator, warm air rises and creates a band of thunderstorms at the ITCZ. The updrafts are a part of the Hadley-cell direct vertical circulation, which moves heat away from the equator. This cell cannot extend beyond about 30° to 35° latitude because Coriolis force turns the upper-troposphere winds toward the east, creating a subtropical jet near 30° latitude at the tropopause. Near the surface are the trade-wind return flows from the east.

    A strong meridional temperature gradient remains at mid-latitudes, which drives westerly winds via the thermal-wind effect, and creates a polar jet at the tropopause. But instabilities of the jet stream cause meridional meanders called Rossby waves.

    These waves are very effective at moving heat poleward, leaving only a very weak indirect-circulating Ferrel cell in midlatitudes. Near the poles is a weak direct-circulation cell. Ocean currents can be driven by the overlying winds in the atmosphere. All these ceaseless global circulations in both the atmosphere and the ocean can move enough momentum and heat to keep our planet in near equilibrium.