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<br />lifted by large-scale forcing. It is a measure of potential for buoyant <br />accelerations of a parcel. <br /> <br />The PBE is a function of the sounding's static stability lapse rate <br />and the vertical profile of moisture. Soundings which have stable <br />layers are affected by lifting. Lifting destabilizes stable layers and <br />advects moisture upward, thereby creating a more favorable atmospheric <br />structure to support convection (Hess, 1959). When the parcel reaches <br />the level of free convection and energy from the environment becomes <br />available for buoyant accelerations, it is considered to become ABE as <br />defined by Chappell and Smith (1975). <br /> <br />The MESOCU model (Kreitzberg and Perkey, 1976) used in this study <br />is a simple, fast, one-dimensional model capable of being used opera- <br />tionally in weather modification projects and forecasting. It simulates <br />several basic processes associated with the development of clouds, <br />including lifting, subsidence induced by convective development, mixing <br />of the cloud into the environment, entrainment, surface eddy mixing, <br />solar heating and subcloud evaporation. <br /> <br />The model is initialized by a vertical profile of temperature and <br />moisture interpolated to 250 m grid levels from significant level data <br />observed in a rawinsonde. In these simulations a convective base is <br />determined from-the initial sounding, and an impulse of 2 m/s is applied <br />to a parcel at this level. The initial parcel radius is specified as <br />2 km. Previous sensitivity studies by Matthews and Henz (1975) showed <br />that 2 m/s initial parcel vertical motion resulted in observed cloud- <br /> <br />50 <br />