In which scenario would air typically rise due to being less dense?

Air typically rises when it is warmed by the Earth's surface because heating decreases the density of the air. As the ground absorbs solar radiation, it warms the air directly above it. This warmer air becomes less dense than the cooler air surrounding it, causing it to rise. This process is a fundamental aspect of atmospheric convection and is essential for various weather phenomena, including the formation of clouds and precipitation.

In contrast, high pressure systems are associated with descending air that tends to create clearer skies as the denser, cooler air sinks. Decreasing humidity generally leads to drier conditions but does not directly cause air to rise; rather, it could lead to stability in the atmosphere. The presence of multiple air masses can influence weather patterns, but the rising of air relates more to its temperature and density rather than the mere existence of different air masses.