What describes the relative movement of two air masses along a cold front?

The relative movement of two air masses along a cold front is characterized by cold air pushing under a warm air mass. This process occurs because cold air is denser than warm air, causing the cold air to advance and displace the warm air upward. As the cold front moves in, the warmer, lighter air is forced to rise rapidly, which can lead to the development of cumulus clouds and thunderstorms. This upward movement of warm air creates instability in the atmosphere, often resulting in precipitation as the warm air cools and condenses.

In contrast, warm air pushing over or under a cold air mass does not accurately describe the dynamics at a cold front, as this scenario typically occurs with warm fronts instead. The unique characteristics of cold fronts distinguish them based on the behavior of the differing temperatures and densities of the air masses involved.