Dynamics of circulations within the stratiform regions of squall lines, The (original) (raw)
THE DYNAMICS OF CIRCULATIONS WITHIN THE STRATIFORM REGIONS OF SQUALL LINES A dynamic version of the two dimensional kinematic cloud model of Rutledge and Houze (1987) has been developed to investigate the effect of microphysics on circulations within the stratiform region associated with mesoscale convective systems. The design of the model allows for specified inputs of hydrometeors, water vapor and heat from the convective region. While there are some disadvantages to this approach, there are also distinct advantages: (1) the complexities of initialization and simulation of a realistic convective line are avoided and (2) many simulations (over 100) were conducted to examine the sensitivity of the results to many physical processes and assumptions. The 10-11 June 1985 PRE-STORM squall line is simulated first, with initialization based upon appropriate soundings, heat budgets and I-D cumulonimbus model results. A 5 km mesh size is used, a value between those typically used in cloud models and in mesoscale models. The model accurately simulates the evolution of the stratiform rain area with a transition zone broadening over time, especially late in the simulation after leading convective elements weaken. Significant ascent is simulated with peak intensities agreeing with observations. In-situ condensate production within the updraft contributes increasingly to the surface rainfall, an,d the ratio of condensate produced within the mesoscale updraft to that advected from the convective line generally agrees with previous water budgets of squall lines. Simulated horizontal flows agree qualitatively with observations, and include a sloping rear-inflow jet that develops with peak magnitudes approaching those observed. Surface rainfall is underestimated as in previous 2D models, possibly implying the importance of 3D convergent forcing of strong ascent in the anvil cloud. Although peak i ACKNOWLEDGEMENTS I would like to thank Prof. Richard Johnson for his guidance, sharing of ideas, and encouragement throughout the doctoral process. Additionally I would like to thank my committee, Prof. Steven Rutledge, Prof. Wayne Schubert and Prof. Reza Zoughi, for their assistance and comments. Special thanks is given to James Bresch for his help with computer programming and debugging during the development of the model. I would also like to thank John Adams for providing the code from the MUDPACK elliptic equation solver.
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