Colloquium: Thursday, Oct. 4, 2007, EN6085A, 2:30 pm.

Airborne reverse flow immersion thermometers were designed to prevent sensor wetting in cloud. Yet there is strong evidence that some wetting does occur, and therefore also evaporative cooling as the aircraft exits a cloud. Numerous penetrations of cumulus clouds in a broad range of environmental and cloud conditions in HiCu-03, RICO-04, and CuPIDO-06 are used to estimate the resulting temperature bias. The cloud-exit “cold spike” relates poorly to most parameters, but most strongly to the dryness of the ambient air. A bias also occurs within cloud, because air is decelerated into the thermometer housing, and thus heated, and thus it becomes sub-saturated. A similar correction for evaporative cooling in clouds leads to higher estimates of cumulus buoyancy and lower estimates of cumulus entrainment than in previous studies.