Cloud liquid water measurement on the armoured T-28: Intercomparison between Johnson-Williams cloud water meter and CSIRO (King) liquid water probe

Abstract

Comparisons are made between liquid water concentration (LWC) readings obtained from a Johnson-Williams (J-W) cloud water meter and a King (Commonwealth Scientific and Industrial Research Organisation) liquid water probe, both mounted on the armored T-28 research aircraft during penetrations of springtime convective storms in Oklahoma and Colorado. The King probe readings are almost always higher, being up to twice those of the J-W instrument in clouds with narrower cloud droplet spectra. In clouds with broader droplet spectra, the ratio often climbs to three or greater. The King probe responds partially to drops larger than cloud droplet size, and also to some ice particles, so its reading can be higher than the cloud LWC present. However, this and earlier comparisons by others indicate that the primary reason for this discrepancy is that the J-W probe often underestimates the cloud LWC due to incomplete response to larger cloud droplets. Thus, published studies involving cloud LWC in convective storms based on readings of the T-28 J-W probe have often overestimated the effects of entrainment and precipitation scavenging on depletion of updraft liquid water, particularly in those areas characterized by clouds with broad droplet size spectra.