Microphysical analysis at the cloud edge of a severe hailstorm

Abstract

Microphysical measurements inside cumulonimbus clouds (Cb) are technically complex and imply some risks. However, data such as the characteristics of the hydrometeors in a cloud, both in liquid and solid phases, their spectrum or the liquid water content are essential to understand microphysical processes inside severe storms as well as the internal structure of the storm. These data can also be used to validate numerical models to characterize severe storms beyond the information provided by the measurements. During a campaign for gathering microphysical data, measurements were carried out through a vigorous cloud turret rising on the flank of a Cb that produced hailstones, at an altitude with temperatures around − 5 °C. Hydrometeor spectra and the liquid water content were determined. The droplet concentration, measured by an FSSP 100, varied a lot depending on the sampling area. The droplet concentration varied inversely when compared to the concentration of larger hydrometeors registered by an OAP 2D2-C. In addition, in some areas supercooled large drops were found to form accumulation zones. The microphysical results have been used to calculate the minimum magnitude of a sustained updraft required to produce supercooled water at an altitude of − 16 °C in adverse conditions for the increase in liquid water due to the presence of ice particle populations.