depression (meteorology)

A meteorological term for a low pressure system at high and mid-latitudes; also known as a cyclone at low latitudes. The system generally passes through a number of well-defined stages, each of which is accompanied by characteristic weather patterns, although not all depressions follow the idealized cycle. A depression is initiated when a wave develops on a front (a boundary between cold and warm air masses). Pressure falls at the crest of the wave. A warm front is the leading edge of the depression, followed by the cold front, with a warm sector between the two fronts. As the cold front travels faster than the warm front, it catches up, to produce an occluded front. When this happens, pressure rises and the depression loses velocity. Surface winds travel anticlockwise around a depression in the N hemisphere, and clockwise in the S hemisphere. Depressions are typically 1000–2000 km/600–1250 mi across, but are temporary features with an average lifespan of 4–7 days. They form regularly in a number of regions (eg along the polar front of the N Pacific and N Atlantic Oceans, and in the Mediterranean). The most intense depressions usually form in winter. Their formation is associated with Rossby waves.

Depression may refer to:

Clinical depression, a medical condition identified by clusters of symptoms such as markedly-decreased mood, motivation, interest, energy levels, etc (also known as "severe depression disorder" or "major depression disorder"). Depression (mood), an everyday term for a sad or low mood or the loss of pleasure. Depression (geology), a sunken geological formation. Depression (economics), a longer-lasting and more severe economic downturn than a recession. The Great Depression, a severe economic recession in the 1930s. Depression (meteorology), an area of low atmospheric pressure associated with cyclones and weather fronts. Depression (physiology), a lowering, in particular a reduction in a particular biological variable or the function of an organ, contrasted to elevation.