Remote sensing ice supersaturation inside and near cirrus clouds: a case study in the subtropics

Abstract

Combining vertically resolved lidar retrievals of water vapor and cloud detection, we document a 2-day subtropical cirrus case study over La Réunion (20.9°S–55.5°E) in March 2005, focusing on the conditions of ice supersaturation inside and near the observed cloud. Using satellite observations, we describe the synoptic conditions leading to cloud formation. Supersaturation occurs 25% of the time within the cirrus, up to 35% in its middle segment, where relative humidity goes beyond 150%. In clear-sky areas, relative humidity stays consistently low, especially in profiles without clouds. High-troposphere atmospheric waves could initiate the formation of supersaturation conditions, especially on 16 March.