What phenomenon is characterized by changes in air pressure due to surrounding weather systems?

The correct choice is pressure gradient, which refers to the difference in air pressure between two areas. This phenomenon drives the flow of air, resulting in wind. When weather systems, such as high and low-pressure areas, come into play, the pressure gradient intensifies, causing variations in air movement and contributing to different weather patterns. Understanding the pressure gradient is essential for pilots, as it can impact flight operations, turbulence, and weather changes.

Microbursts are localized downdrafts of air that can occur in thunderstorms, leading to strong winds that descend rapidly. Thunderstorms themselves are complex weather systems characterized by strong winds, heavy rain, and potential lightning, but they are not specifically defined by the air pressure differences in the surrounding atmosphere. Humidity shifts refer to changes in moisture content in the air, which can influence weather but do not directly relate to pressure variations. Thus, while these phenomena all relate to weather, the pressure gradient is specifically about the changes in air pressure resulting from surrounding weather systems.