21.12 Atmospheric Circulation and Atmospheric Cells

21.12 Atmospheric Circulation and Atmospheric Cells

The conservation of angular momentum of Earth plays an important role in shaping the moving air patterns. Atmospheric circulation is significantly affected by the conservation of angular momentum and Earth's rotation. The angular momentum of an air mass about Earth's rotation axis is given by $L = mvr$, where $m$ is the mass of the air, $r$ is the distance from the rotation axis, and $v$ is the velocity. In atmospheric science, we usually consider specific angular momentum, which is the angular momentum per unit mass as follows:

As air moves from the equator toward the poles or vice versa, it retains its specific angular momentum at its original latitude. As the air mass moves, $r$ decreases and so $v$ increases to keep $rv$ constant. As the Earth rotates faster at the equator than at higher latitudes, air moving toward the pole from the equator lags behind the rotation of the surface beneath it. This results in an apparent deflection of the moving air due to Earth's rotation and this type of effect is called Coriolis Effect.

(Fig. 21.14: Schematic representation of formation of atmospheric cells during atmospheric circulation of Earth.)

Tidbit!

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The Dead Sea is so salty that people float effortlessly, the density is extremely high due to salt concentration.

Brain Teaser

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In the polar regions, seawater becomes saltier as ice forms. How does this affect ocean circulation, and what process does it drive?

The deflection occurs toward right in the northern hemisphere and to the left in the southern hemisphere. This deflection does not affect the speed of the air but changes its path, creating curved wind patterns. These deflected air flows lead to the formation of three distinct atmospheric circulation cells in each hemisphere: the Hadley cell, Ferrel cell, and Polar cell. A schematic diagram representing the formation of atmospheric cells during atmospheric circulation is shown in Fig. 21.14.