Answer:
Stage 4 in the Polar Front theory is called the occlusion stage.
Step-by-step explanation:
The Polar Front theory describes the life cycle of a mid-latitude cyclone, which is a type of cyclone that forms along the polar front, the boundary between cold polar air and warmer air from the tropics. The life cycle of a mid-latitude cyclone is divided into several stages, and stage 4 is known as the occlusion stage.
During the occlusion stage, the cold front of the cyclone catches up and overtakes the warm front. This occurs when the cold air associated with the cold front undercuts the warm air associated with the warm front, lifting the warm air mass off the surface. As a result, the warm air is separated from the surface and forced aloft.
The occlusion stage is characterized by the formation of an occluded front, which is a combination of the cold front and the warm front. The occluded front wraps around the cyclone, marking the area where the warm and cold air masses meet.
In this stage, the cyclone reaches its maximum intensity, and the central pressure begins to rise. The occlusion stage is often associated with strong winds, heavy precipitation, and sometimes severe weather, such as thunderstorms or tornadoes.
In summary, stage 4 in the Polar Front theory is called the occlusion stage. During this stage, the cold front catches up with and overtakes the warm front, leading to the formation of an occluded front. This stage is characterized by the maximum intensity of the cyclone, with strong winds, heavy precipitation, and potential severe weather.