Primary Atmospheric Circulation

The Sun’s unequal heating of Earth creates spatial pressure differences that drive the primary atmospheric circulation. The pressure gradient force moves air from higher to lower pressure. The Coriolis effect (apparently, to us) deflects winds to the right (left) in the Northern (Southern) Hemisphere, and frictionFriction slows the wind and therefore weakens the Coriolis effectCoriolis effect. Quasi-permanent pressure-derived features include the two Hadley cellsHadley cell, which have rising motion and low pressure knownHumidityand Africaand inter-tropical convergence zone as theEnergyand inter-tropical convergence zone inter-tropical convergence zone (ITCZ) near the Equator andInter-tropical convergence zone (ITCZ)and humidity sinking motion with high pressure at the subtropical anticyclones near 30° N and 30° S latitude, with trade windsWindsoutheast trade between them and the subtropical jet streamSubtropical jet stream flowing aloft near the Hadley cells’ poleward edges. Rising motion at the subpolar lowsSubpolar low near 60° N and 60° S and sinking air and high pressure near both poles support the near-surface polar easterliesWindpolar easterlies. The mid-latitudes of each hemisphere have near-surface westerly windsWindeasterlies, polar. West-to-east flow also prevails aloft over the extratropics of both hemispheres, with embedded poleward-bending ridges and equatorward-bending troughs within a continuousHumidityand Africaand Rossby waves belt of Rossby wavesRossby wave andand humidity theJet streamAfrican easterlypolar front polar frontFront (weather)polar jet stream circumnavigating each pole. The ridge-to-trough sideand humidityridge-to-trough side of the Rossby waveRidge-to-trough side of Rossby wave generally supports clear skiesHumidityand Africaand trough-to-ridge side of Rossby wave while theTrough-to-ridge side of Rossby waveand humidity trough-to-ridge sidetrough-to-ridge side supports surface cyclones and cloudy conditions.