The Dynamics Of Circulations Within The Trailing Stratiform Regions Of Squall Lines .2. Influence Of The Convective Line And Ambient Environment

A dynamic version of the two-dimensional kinematic cloud model of Rutledge and Houze is used to study the individual roles of hydrometeor and heat advection from the convective line to the stratiform region of the 10-11 June 1985 PRE-STORM squall Line. The design of the model allows for specified inputs of hydrometeors, heat, and water vapor from the convective line.Convective heating alone generates significant ascent and condensate in the anvil; however, surface rainfall is scarce without the advection of hydrometeors from the convective line. Hydrometeor advection alone does not produce strong ascent in the anvil cloud, implying the important additive effects of both heat and hydrometror advection in generating broad regions of significant stratiform rainfall.The roles of individual microphysical processes within the stratiform region are examined, alone with the sensitivity of stratiform region dynamics to postconvective region environmental conditions. Of the processes evaporation, melting, and sublimation-evaporation in mesoscale downdrafts is the most important affecting the intensity of circulations such as the rear-inflow jet and precipitation-followed by melting and then sublimation. Stability strongly controls vertical motion in the stratiform region. Greater instability increases in situ production of condensate, surface rainfall, and low-level drying within the mesoscale downdraft. The intensity of hydrometeor advection from convective elements significantly influences surface rain rates in the stratiform region. These findings suggest that natural variability arising from three-dimensional convective line structures and inhomogeneities in the environment can induce significant hydrometeor and flow perturbations (asymmetries) in the trailing stratiform regions of squall lines.