front

front in meteorology, zone of transition between adjacent air masses . If a cold air mass is advancing to replace a warmer one, their mutual boundary is termed a cold front; if the reverse, then the boundary is termed a warm front, whereas a stationary front indicates that no relative advance of either air mass is occurring (see illustration) . An occluded front is one in which a warm front has been completely undermined by cold air and is therefore positioned aloft. Since warmer air always overrides colder, denser air, the frontal boundary is sloped closer to the horizontal than the vertical. A mature cyclone usually involves all of the frontal types. The recognition of atmospheric fronts and their relative importance to weather forecasting came about only at the beginning of the 20th cent. as a result of publications by the meteorologists Vilhelm and Jakob Bjerknes .

front The boundary or boundary region that separates air masses of different origins and characteristics. Temperature gradients in any horizontal surface are large through the front. Different types of front are distinguished according to the nature of the air masses separated by the front, the direction of the front's advance, and the stage of development. The term was first devised during World War I by the Norwegian school of meteorologists (headed by Professor V. Bjerknes). See also anafront; cold front; katafront; occluded front; polar front; and warm front.

front Boundary or boundary region separating air masses of different origins and characteristics. Temperature gradients in any horizontal surface are large through the front. Different types of front are distinguished according to the nature of the air masses separated by the front, the direction of the front's advance, and the stage of development. The term was first devised during the First World War by the Norwegian school of meteorologists (headed by Prof. V. Bjerknes). See also ANAFRONT; COLD FRONT; WARM FRONT; KATAFRONT; OCCLUDED FRONT; and POLAR FRONT.