Definition
Lower part of the terrestrial ATMOSPHERE, extending from the surface up to a HEIGHT varying from about 9 km at the POLES to about 17 km at the EQUATOR, in which temperature decreases fairly regularly with HEIGHT. From an analogy with the ATMOSPHERE, the term is sometimes applied in OCEANOGRAPHY to the upper ocean layer of relatively high temperature that is found in middle and lower LATITUDES and within which strong CURRENTS are present. See STRATOSPHERE.