Damaging Surface Hail in Simulations of Satellite-Detected Hailstorms in Australia's Tropics

Abstract

Satellite detections of hail signatures are uncertain in the tropics, where the deep troposphere and a warm, humid sub-cloud environment increase the chances that ice detected aloft will melt before it reaches the surface. It is often suspected that satellite-based detections of hail over the tropics are over-estimations owing to this effect. Here, we used numerical weather simulations to examine the plausibility of damaging surface hail at times and locations when satellites detected hail signatures over Australia's tropics. Four microphysics schemes were used to simulate 61 hail signature detections with surface hailstone sizes estimated using a column model for hailstone growth and melting, and estimated by model microphysics. Using the column model, 65 of the 244 simulations were “damaging-hail cases” that produced surface hail at least 20 mm in diameter. Although instability was not significantly different between the no-hail and damaging-hail cases, damaging-hail cases had increased wind shear and mid- to upper-level moisture, and produced storms with wider and stronger updrafts than no-hail cases. These hail cases could therefore support the growth of larger hailstones that survived melting to reach the surface. The results are well explained by entrainment theory. These simulations show that satellite-based hail detections in the tropics may plausibly contain a significant subset of damaging surface-hail events.