Clouds Blowing in the Wind: Momentum Transport in Cloudy Boundary Layers Observed From Collocated Wind Lidar and Cloud Radars and Simulated With Dales

Abstract

Convective clouds may be associated with substantial transport of momentum. Much of what we know about convective momentum transport stems from high-resolution simulations because high-resolution measurements of the wind profile are rare. This study exploits ground-based remote sensing techniques to visualize wind below and within clouds and their surroundings, to assess momentum transport. The Tracing Convective Momentum Transport in Complex Cloudy Atmospheres experiment (CMTRACE) took place at the experimental Cabauw site (The Netherlands) between 13.09.2021 and 03.10.2021. The goal of CMTRACE was to provide continuous profiles of horizontal and vertical wind with a temporal resolution of ~1 minute and vertical resolution of ~50 m within the cloud and sub-cloud layers to improve our understanding of the role of momentum transport from cloud- to mesoscales. A scanning wind lidar provided the observations in the sub-cloud layer, while in the cloud layer, one scanning and one vertically pointing cloud radar provided observations. During CMTRACE, we sampled various cloud regimes including non-precipitating shallow cumulus clouds, deep convective clouds and stratiform clouds. In this study, we illustrate some of the most interesting CMTRACE observations that reveal the circulations (winds) near clouds and present statistical analyses as a function of different cloud regimes. Specifically, we calculate profiles of wind fluctuations and their cross-correlations to address the momentum flux carried on cloud- and mesoscale scales. The observations from different cloud regimes (e.g. clear sky, shallow convection and frontal passage) are compared to momentum fluxes and wind variability in the Dutch Large-Eddy Simulations nested on the experimental site for the selected days.