Hadley cells develop because the equatorial and tropical regions are heated more intensely than the higher latitudes,
causing thermal circulations.
- These loops drive the northeast and southeast trade winds, the convergence and lifting of air at the intertropical
convergence zone (ITCZ), and the sinking and divergence of air in the subtropical high-pressure belts.
Surface air moving poleward from the subtropical highs forms the midlatitude westerlies.
- The polar front forms where this warm subtropical air meets the cold, dry air moving equatorward out of the
The ideal circulation over the Earth is modified by the seasonal changes in land–sea temperature contrasts.
- These contrasts produce monsoon circulations over low-latitude continents. In addition, they produce seasonal
changes in the midlatitude circulations over the northern hemisphere continents and oceans.
Winds in the atmosphere are dominated by a global pressure gradient force between the tropics and pole in each
The global pressure gradient force and the Coriolis force generate strong westerly geostrophic winds in the upper
atmosphere called jet streams.
- These jet streams are concentrated westerly wind streams with high wind speeds located near the tropopause.
Disturbances in the jet stream develop in the upper-air westerlies, bringing cold, polar air equatorward and warmer,
subtropical air poleward
Oceans show a warm surface mixed layer, a thermocline, and a deep cold layer. Near the poles, the