2.4.5—Tricellular model

Rising air tends to bring rain; sinking air tends to suppress clouds, so circulation cells help explain biome belts by latitude.

Unequal solar heating drives three circulation cells in each hemisphere: Hadley cells from the equator to about 30°, Ferrel cells through the mid-latitudes, and polar cells at high latitudes. Warm moist air rises near the equator, bringing rain; descending air near 30° creates dry subtropical belts, while further rising and sinking zones help create mid-latitude and polar climate patterns.

A region near 30° latitude may be desert-prone because descending air warms and dries, limiting cloud formation.

The equatorial rising branch of the Hadley cells is generally wet; the descending branches near 30° are generally dry.

Latitude is a clue, not a guarantee; mountains, currents and seasonal circulation modify the pattern.