Circulation cells

Between the Equator up to 30° latitude (N or S), we find the Hadley cell.
In the Equatorial region, air is heated and rises, creating a low pressure area. Air would tend to shift towards the N along the meridians, but in the northern hemisphere, due to the Coriolis effect, the flow is deviated towards NE and descends toward the 30° parallel, bringing warm humid air. Once it descends, the air is again drawn towards the Equator due to the low pressure of the area, and this time the air travels from NE to SW, again as a result of the Coriolis effect. This movement gives origin to the NE trade winds. The same occurs in the southern hemisphere where the trade winds blow from the SE. The area where the NE trade winds clash and converge with the SE trade winds creates an equatorial low pressure area characterized by precipitations and violent perturbations, the so-called area of equatorial calm, that gets its name due to the low pressures and low wind speeds. Between the 30° and 60° latitudes, instead, in both hemispheres the Ferrel cell is active. It rotates in the opposite direction to the Hadley cell. Converging with the margin of Hadley’s Cell, a tropical high pressure area is created, around 30°, the so-called horse latitudes area, where the winds blow from the SW on ground, the westerlies which however have a more irregular trend than the trade winds. In this belt there are a series of anti-cyclonic nuclei, among which the Azores anticyclone whose seasonal movements determine the weather in our regions. The masses of air from the Ferrel cell move back to the higher altitudes around the 60° latitude, where the area of sub-Polar low pressure is formed.
In the higher latitudes the Polar cell forms, which has the same trend as the Hadley cell with easterlies at ground level and westerlies at higher altitudes. The Polar cells are the least extended, but thanks to the Polar high pressures, these have the important task of transferring the freezing polar air to the middle latitudes in the Ferrel cell.

Special reports

From the Multimedia section

Facts