Depression Slides
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A depression forms when warm and cold air masses meet at a polar front boundary. As the denser cold air advances, it undercuts the warm air, forming a warm front and cold front. Eventually the cold front catches up to the warm front, lifting it in an occluded front. The depression then decays as the warm air is lifted away, with warm air now trapped on the poleward side of the polar front.
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Depression Slides
- 2. 1) Initiation: Depressions begin to form when a tropical air mass meets a polar air mass (polar front boundary between cold and warm air) to form a vortex of anticlockwise swirling air. Instability occurs on the polar front. 2) Growth and development stage: The less dense warm air rises over cold air. The boundary between the two forms the warm front. The colder advancing air to the west is denser and undercuts the warmer air. The boundary forms the cold front. In between is a warm sector. 3) Occluded stage: The cold front moves faster than the warm front and eventually catches it up and lifts it away from the ground, forming an occluded front. 4) Decay stage: After occlusion the depression dissolves as the warm air has been lifted away. Warm air is now trapped on poleward side of polar front. How depressions are formed A depression brings rapidly changing weather, which nevertheless follows a pattern . The stage a depression is at when it passes will influence the nature of its impact. Further variation is provided by the nature, type and temperature differences between the converging air masses which form the system. Key point: a depression is a weather system where a cold front is chasing a warm front . 1 2 3 4