What happens to relative humidity when a mass of air descends?

When a mass of air descends, the pressure exerted on it increases due to the weight of the air above it. As the air descends and the pressure increases, the temperature of the air also typically increases due to adiabatic compression. Since warmer air can hold more moisture compared to cooler air, the relative humidity decreases as the temperature rises.

Relative humidity is defined as the amount of moisture in the air compared to the maximum amount of moisture the air can hold at that temperature. When the air descends, even if the absolute amount of moisture remains constant, the increase in temperature due to compression means that the air is now capable of holding more moisture than before. Consequently, the relative humidity drops because the air is less saturated with water vapor relative to its new capacity at the higher temperature.

This process is essential in meteorology as it impacts weather patterns, cloud formation, and precipitation. Understanding the dynamics of air movements and their effects on humidity is crucial for predicting weather conditions effectively.