Anatomy of cirrus clouds

Abstract

The Emerald airborne measurement campaigns have provided a view of the anatomy of cirrus clouds in both the tropics and mid-latitudes. These experiments have involved two aircraft that probe cirrus clouds from outside and from within. One aircraft, the Egrett, flew within the cloud with instruments for in-situ sampling of ice crystals, humidity, and turbulence. Another aircraft, the King Air, flew directly below the cloud with an upward viewing lidar to map the cloud structure. The airborne lidar measurements were used as a guide for the experimenters to conduct flight patterns with the Egrett sampling at various altitudes within the same cirrus fall-streaks. Results are presented here from two separate flights: one in frontal cirrus above Adelaide, Australia, and the other in the cirrus outflow from convection above Darwin. Recorded images of ice crystals are shown in relation to the cloud structure measured by the lidar. In mid-latitude frontal cirrus, columnar and irregular ice crystals were observed throughout the cloud while rosettes were found only at the top. The cirrus outflow from tropical thunderstorms was found to be composed of similar shapes in addition to hexagonal plates and large crystal aggregates. As the cloud drifted away from the convection the plates and smaller aggregates were found at the top while large aggregates had sedimented to lower regions of the cloud.