A Sublimation-initiated Mesoscale Downdraft and Its Relation to the Wind Field below a Precipitating Anvil Cloud

Abstract

Abstract A simple, one-dimensional model is developed to examine the potential for a sublimation-initiated mesoscale downdraft to influence the dynamics of the subanvil region by advecting horizontal momentum from a high-level precipitating anvil cloud downward into the middle or lower troposphere. Model results suggest that this vertical advection can occur on a time scale of several hours or less, although it is found to be highly dependent upon the snow mixing ratio within the overlying anvil cloud and lapse rates in the environment below. The study is motivated by an examination of data from a 50-MHz radar wind profiler on 24 June 1985 that suggests downward momentum advection from anvil base may have produced unbalanced flow in midlevels, owing to strong flow within the anvil and weak midlevel geostrophic winds. For this situation, we hypothesize that as the anvil cloud both dissipated and was advected horizontally away from the profiler site by the strong, upper-level winds, the downdraft weakened a...