Application of Slice Theory to Account for the Horizontal Extent of Convective Precipitation Radar Echoes

Abstract

Classical slice theory modified to take account of mixing and entrainment is used to explain the areal extent of 10-cm convective radar echoes in nonconvergent, barotropic situations in the subtropics. Relative humidity in the layer of convective cloudiness, which is taken as a measure of the ability of mixing and entrainment to destroy buoyancy and evaporate clouds, correlates very significantly with the ratio of observed scope coverage to slice-indicated maximum updraft area. Furthermore, the computed slice updraft area exceeds the observed scope coverage in all cases where surface convergence was absent. Incorporation of saturated air descent into the slice equations is performed in Appendix 1. The results show that the presence of saturated downdrafts increases the updraft area by an amount that is directly proportional to the area and velocity of these downdrafts.