Question

How does subsidence at the storm's periphery make surface air relatively dry there?

Answer 1

Subsidence at the storm's periphery makes the surface air dry due to the rain shadow effect, where air descending on the leeward side of mountains warms and carries less moisture. Subsidence also occurs in high-pressure areas surrounding storms, leading the air to warm and dry as it moves downward.

Step-by-step explanation:

Subsidence at the storm's periphery causes surface air to become relatively dry due to the rain shadow effect. This phenomenon occurs when moist air ascends over high elevations, such as mountain ranges, leading to cooling and condensation which causes precipitation on the windward side of the mountains. As the air descends on the leeward side, it warms and becomes drier, leading to semi-desert or desert conditions due to lack of precipitation.

An example of this can be seen in the dryness of the North American deserts like the Mohave and Sonoran, where evaporation often exceeds precipitation, and similar processes contribute to the dryness of the Sahara and Namib deserts. In a storm context, particularly around tropical storms or hurricanes, subsidence can occur when the high-pressure systems outside the storm's core cause air to move downward.

This sinking air increases in temperature and decreases in relative humidity as it compresses, which leads to dry conditions surrounding the storm. While low-pressure systems typically instigate weather events with ascendant, moist, and condensing air, these are complemented by subsiding air in high-pressure situations.

Answer 2

Subsidence is simply sinking air. As air sinks it warms adiabatically due to increasing pressure as it sinks. As air warms it can hold more water vapor. The sinking air warms but does not acquire more water vapor thus its relative humidity decreases,thus the relative dryness that results.