Unified Very Low Stratus Cloud/Subcloud Microphysics Model
ARMY LAB COMMAND WHITE SANDS MISSILE RANGE NM ATMOSPHERIC SCIENCES LAB
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A model is presented for simulating very low stratus clouds and their associated subcloud regions. This model is based on the assumption that the atmosphere contains particles that can be chemically and physically characterized and that grow in the presence of moisture as a function of relative humidity, temperature, and the size and chemistry of the particles. Components of this model include droplet growth and evaporation, phase change and mass balance of total water, thermodynamics, and ascent of a cluster of drops enclosed in moist air. The model requires only limited user input some conventional meteorological values at a reference height 2 m above ground level and some parameter values and other specifications. Input values for a visibility parameter and relative humidity are used with a choice of air mass type to define the parameters of a truncated bimodal lognormal drop size distribution at the reference height. Vertical profiles of drop size distributions can be simulated and used for further analysis. Examples are shown for modeled vertical profiles of lapse rate, temperature, potential temperature, mass loading, relative humidity, drop size, and drop concentration.