Height‐resolved variability of midlatitude tropospheric water vapor measured by an airborne lidar

Abstract

Free tropospheric water vapor variability, measured by airborne lidar over Europe during summertime, is analyzed at altitudes from 2 km to 10 km. Horizontal structure functions of specific humidity were computed and show power‐law scaling between about 10 km to 100 km in range. The second‐order structure function shows scaling exponents equivalent to spectral slopes that vary from around 5/3 in the lower troposphere to 2 at upper levels. More specifically humidity smoothness typically increases with height, while intermittency decreases. A classification of the data according to whether the series occurred above or below the level of nearby convective cloud tops gives a separation of the scaling exponents in the two air masses. 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.

The global distribution of cloud gaps in CALIPSO data

“…Nevertheless, physically they are closely related to the distribution of relative humidity. Recently, similar power-law exponents have been reported for specific humidity variability seen in airborne lidar measurements by [5,6]. Meso-scale relative humidity variability is more strongly tied to specific humidity variability than to temperature variability, as temperature fluctuations are likely to be damped by gravity waves through their effect on buoyancy [17].…”

Horizontal structure function and vertical correlation analysis of mesoscale water vapor variability observed by airborne lidar

“…The paper focuses on the particular strengths of airborne lidar data, namely high horizontal and vertical resolution, to characterize the scaling behavior of water vapor in different air masses. The work extends the preliminary results of Fischer et al [] who identified different scaling laws for convective and nonconvective air masses sampled during a field campaign over western Europe in summertime. Here the analysis is extended to include data from subtropical and polar regions in autumn and winter, respectively.…”

“…The analyzed observations in the paper of Fischer et al [] show that first‐order scaling exponents and the intermittency exhibit significant vertical variability during summertime over Europe. The present work gives an analysis of a much larger data set with a larger geographical extent, including data from a polar region and from a subtropical region.…”

Aviation Turbulence

“…Zilberman et al (2008) retrieve spectral characteristics from aerosol concentration measurements with ground-based lidar and allude to the complex relationship between the aerosol spatial spectrum and the spectrum of the underlying turbulence. Airborne water vapor measurements with lidar (Fischer et al 2012) display variance spectra in general accordance with turbulence models, at least for the convective troposphere on rather large scales. These studies hint at the potential of passive tracer variance analysis for the determination of turbulence properties.…”