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<br />(Qe) in the inflow zone of these storms was nearly constant <br />with height in the subcloud region; however~ large horizontal gradi- <br />ents existed at the edge of the inflow air. This air was negatively <br />buoyant (Marwitz~ 1972a; Foote and Fankhauser~ 1973) suggesting that <br />mechanical lifting rather than buoyant processes were responsible for <br />initiation of moist convection. Fankhauser (1976) concluded that the <br />release of latent heat with strong updrafts was the most likely <br />driving force in vigorous thunderstorms. He hypothesized that <br />non-hydrostatic pressure forces (AP > 1 mb) could result from upward <br />accelerations and sustain the inflow of negatively buoyant air. Sail <br />plane measurements in NHRE storms also showed an excellent correla- <br />tion between updraft speed and Qe~ further indicating the value <br />of Qe as a tracer of regions of vertical motion. <br /> <br />Squall lines have been studied extensively in the mid-latitudes <br />because of their importance in producing severe weather such as <br />tornadoes~ hail and damaging winds (e.g.~ Tepper, 1950; Newton~ 1950; <br />Fujita~ 1955; Bates~ 1961; House~ 1959; Miller~ 1967; Dirks~ 1969). <br />These types of meso-almeso-B systems tend to be linearly organized in <br />response to the synoptic-scale flow ahead of advancing cold fronts. <br />They develop in regions of strong horizontal pressure gradients with <br />large vertical and horizontal wind shears where conditional instabil- <br />ityand abundant moisture exist. In these cases~ the linear struc- <br />ture is imposed and modulated by synoptic-scale features described by <br />Sanders and Emanuel (1977)~ Emanuel (1979~ 1982). The boundary-layer <br />convergence ahead.of a surface front~ a narrow tongue of moist~ <br />unstable air in the warm sector~ a strong short-wave trough at <br /> <br />15 <br />