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<br />1058 <br /> ""j <br /> 11,0 <br /> 12,0 <br /> 10.0 <br />E <br />"" <br />to< 8,0 <br />::c <br />(9 <br />w <br />::c <br /> 6.0 <br /> 1.0 <br /> 2,0 <br /> . <br /> 0.0 ~ <br /> 0.0 <br /> <br />MONTHLY WEATHER REVIEW <br /> <br /> <br />VOLUME 108 <br /> <br />TIME or L1rTING 12 <br /> <br />20 KPA <br /> <br />30 KPA <br /> <br />50 KPA <br /> <br />70 KPA <br /> <br />80 KPA <br /> <br />I 1 <br />0,5 1.0 <br />MAGNITUDE Of LI~T IKMI <br /> <br />, <br />I.S <br /> <br />FIG. 2. Two profiles of lifting used in modeling experiments which simulate 10 <br />cm S-1 (dashed) and 20 cm S-1 (solid) lifting at the 70 kPa level (3,1 km MSL), <br /> <br />et al., 1976), radar observations of gravity wave <br />amplitudes (Gossard and Richter, 1970), and meso- <br />scale convergence observed in surface. mesoscale <br />networks in Florida (Ulan ski and Garstang, 1978) <br />and in Texas.1 <br />In these simulations a measure of the magnitude of <br />lifting is the vertical distance (km) through which <br />each parcel in the modeled atmosphere is lifted <br />during each hour simulated, so that a 10 cm S-1 <br />lifting rate would result in a maximum lifting of 360 m <br />at the level of nondiyergence each hour. A level of <br />nondivergence of 70 kP A was assumed for meso- <br />scale triggering in contrast to the synoptic-scale level <br />of nondivergence of -60 kP A. This assumption was <br />based on mesoscale observations indicating more in- <br />tense low-level forcing. 1 <br />Three-hour sequences of convective development <br />were simulated using identical initial conditions of <br />cloud updraft radius (2.0 km) and initial parcel <br />vertical velocity (2.0 m S-I). The mesoscale lifting <br />impulse was applied at the end of each hour's con- <br />vective development such that the subsequent hours <br />simulated were destabilized by the large-scale forc- <br />ing which balanced the local stabilizing effects of <br />cloud-induced subsidence. The arithmetic sum <br />of the depths of all clouds formed by the one-dimen- <br />sional steady-state cloud model (Fig. 1) for each 3 h <br /> <br />1 Scoggins, R. S., G, S. Wilson and S, F, Williams, 1979: <br />Mesoscale characteristics of the Texas HIPLEX area during sum- <br />mer 1977, Texas Department of Water Resources, Rep. LP. 99, <br />Prepared under Contract 14-80002 by Texas A & M University <br />funded by U,S. Department of the Interior and the Texas De- <br />partment of Water Resources, ' <br /> <br />simulation of cloud-environment interaction is taken <br />as a measure of the thermodynamic potential for <br />convective cloud growth of each sounding. This total <br />depth of all clouds in each sequence of growth is <br />referred to as the convective potential index (CPI). <br />The CPI is a simple measure of the relative potential <br />for convective cloud development which may be <br />realized when synoptic or mesoscale lifting creates <br />Potential Buoyant Energy that can be converted into <br />Available Buoyant Energy. <br />The numerical experiments were performed on <br />232 rawinsonde observations taken during the sum- <br />mers of 1975, 1976 and 1977 at Big Spring, Texas, <br />Goodland, Kansas, and Miles City, Montana (Table <br />1). The rawinsonde observations for 1976 and 1977 <br />that were used to initialize the model simula- <br />tions were selected from days with either 1) or- <br />ganized mesoscale convective clouds, e.g., lines <br />or clusters, which indicate the existence of a <br />mesoscale-triggering mechanism that may result in <br />lifting, or 2) isolated or random convective clouds <br />or clear skies. GOES-TAP satellite imagery from <br />the National Environmental Satellite Service was <br />used to visually classify each day's convective cloud <br /> <br />TABLE 1. Number of rawinsonde cases examined <br />by site and year. <br /> <br />Site <br /> <br />Number <br /> <br />Year <br /> <br />Miles City, Montana <br />Goodland, Kansas <br />Big Spring, Texas <br />Total <br /> <br />120 <br />56 <br />56 <br />232 <br /> <br />1975 <br />1976, 1977 <br />1976, 1977 <br />