What defines a warm front in meteorology?

A warm front in meteorology is defined as a boundary where warmer air rises and replaces colder air. This occurs because warm air is less dense than cold air, causing the warm air to ascend over the colder, denser air mass. As the warm air rises, it cools, which can lead to cloud formation and precipitation. This process is integral to understanding weather patterns, particularly the gradual changes associated with the passage of a warm front.

In contrast, the other options describe different meteorological phenomena. The first choice describes a cold front, where cold air is actively pushing under warm air, leading to more abrupt changes in weather. The third choice references a zone of heavy rain and storms, which can occur within various types of fronts but is not specific to warm fronts. The last choice, describing a transitional area between high-pressure systems, does not pertain specifically to warm fronts and is more general in nature.