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Jean-Jacques Morcrette and Christian Jakob

operational forecasts are performed with the maximum-random cloud overlap assumption. This paper reports results of simulations obtained with the operational radiation scheme including either the RAN, the MAX, or the MRN cloud overlap assumption, within both the framework of the one-dimensional version of the ECMWF physics parametrization, and that of the three-dimensional model (RAD simulations). As important as the changes in cloud radiative forcing can be, they are only one element in what contributes

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J. M. Reisner and C. A. Jeffery

solution to minimize numerical issues near cloud boundaries. Two particular items distinguish the current SC modeling approach from other traditional approaches. First, it is required that the entire equation set converge within the JFNK solution procedure, thus mandating within the discrete model that the smallest values for cloud quantities are near the Newton tolerance. But, the small background values have little impact outside of cloud boundaries with these values being subtracted from forcing

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John B. Cunning, Henry W. Poor, and Mark Demaria

inconvective storm development and show the importance of boundary layer forcing in the development ofconvective clouds in the Horida environment. Analysis of the temporal evolution of cloud mass at 600-mintervals in the vertical shows that below 3 km the two cumulonimbus systems appeared to evolve to about thesame size, with significant differences occurring above that level. The increase in cloud mass at some levelsabove 3 km in the second convective system (System II) were more than twice as large as

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Robert Solomon and Marcia Baker

of early electrificatio~ in thunderstorms, together with observations of aseries of summer thunderstorms in New Mexico, to understand the roles of certain environmental factors indetermining thunderstorm electrification. The results suggest that development of lightning depends sensitivelyon rcz, the duration of significant updrafts in the charging z6ne between -10- and -25-C. Model tests suggestthat rcz is maximized for moderate cloud-base forcing and,that rc~ depends on enwronmental parameters

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U-2 flight was part of the US. AirForce High Altitude Clear Air Turbulence program. Pertinent findings include: (1) location of the tropopause justabove the cloud tops at 54,000 ft (100 mb) with a temperature of -86OC, 12'C lower than the mean; (2) a verticaltemperature rise of 11C in a few hundred feet just above the tropopause; (3) horizontal temperature changes up to7C and smooth flight conditions in the stable layer above the cloud tops; and (4) small temperature fluctuations andgenerally

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Thomas Rickenbach, Paul Kucera, Megan Gentry, Larry Carey, Andrew Lare, Ruei-Fong Lin, Belay Demoz, and David O’C. Starr

; Machado et al. 2002 ) of a systematic shift in time between the diurnal maximum of near-surface rainfall and of the cloud-top area (or of rainfall based on infrared cloudiness). Moreover, the present result predicts that the time shift would increase for larger, stronger, and rainier systems, which may be tested in model simulations. This also has implications for model parameterization of latent heat (related to rainfall) and radiative forcing (related to the cloud-top area) of tropical cloud systems

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Adrian M. Loftus, Daniel B. Weber, and Charles A. Doswell III

avenue to follow, therefore, was to replace the IB with a mechanism for producing sustained ascent. For simplicity, it was assumed that the time scale of such ascent would be much longer than that of a deep convective cloud, which has a time scale associated with how long it takes an air parcel to rise through the depth of the cloud (of order 20 min). Thus, at least to begin the study, we assumed that the forcing for ascent would be constant in time; this is not necessary, but it does represent a

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Jonathan E. Martin

first to identify this important cloud and precipitation producing airstream, as the foregoing discussion indicates. It is, however, the first to directly relate it to the three-dimensional occluded structure and, more importantly, to the dynamical forcing that supports its ascent in the occluded quadrant of cyclones. The current analysis also supports the aforementioned investigations in suggesting that the western extension of the cyclone comma head cloud shield sometimes results from cyclonically

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Keith Brill and Bruce Albrecht

the partitioning of the solar heating between the top half of the cloud layer and theinversion. The variations due to divergence and solar radiation appear to contribute additive[y to the totaldiurnal variation of the model inversion height. The observations and model results support the conclusion that significant diurnal variation of the tradewind boundary layer bccurs and is primarily due to the diurnal variation of radiative forcing and secondarilyto diurnally varying large-scale divergence

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George S. Young and Todd D. Sikora

northwest of the Gulf Stream North Wall yields a bulk surface sensible heat flux of 0 W m −2 while the inferred value over the Gulf Stream was 120 W m −2 . Thus, the thermodynamic forcing was similar to that in the previously discussed mesoscale band cases. The synoptic setting was likewise similar with cold advection occurring in the northerly and northwesterly boundary layer flow west of a cold front (not shown). Yet, despite these similarities, the 20 March case lacked mesoscale- β cloud bands. The

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