Airborne lidar observations of mid-latitude upper-tropospheric water vapour variability

Abstract

In order to characterize moisture variability in the troposphere, we have analysed long-range airborne differential-absorption lidar observations of water vapor measured during the COPS (Convective and Orographically-induced Precipitation Study) experiment conducted in summer 2007 by computing structure functions throughout the troposphere from 2 km up to 10 km. The specifc humidity variations over middle and south Europe show scaling from about 10 km to 100 km in horizontal range. The scaling laws show different characteristics at different heights. Typically humidity smoothness increases with height, while intermittency decreases. The results are consistent with a water vapor distribution determined at upper levels by a downscale cascade of variance by advective mixing, but increasingly influenced at lower levels by local injection of humidity by moist convection.