Mass flux in continental shallow cumulus clouds: large-eddy simulation versus long-term radar observation

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Description

Summertime observations for 13 years at Atmospheric Radiation Measurement Southern Great Plains (SGP) site are used to study air motion in non-precipitating fair-weather shallow cumulus clouds. A composite shallow cumulus case is constructed based on an ensemble of days with observed active shallow cumulus clouds. Large-scale forcing for this composite case and individual cases are derived accordingly based on observation-constrained variational analysis and are used to drive the large-eddy simulation (LES), whose set-up is most suitable to make an apple-to-apple comparison with radar observation at the site. At the same time, a novel retrieval algorithm, which can remove the insects’ contamination on radar reflectivity, is applied to millimeter cloud radar 10s observations to get vertical velocity of air motion in the shallow cumulus cloud ensembles. Together with cloud fraction observation, mass fluxes are derived. We focus on the behavior of cloudy profiles with liquid water path greater than 80 g/m^2, because we believe this portion of clouds makes a major contribution to the total mass flux and by so doing, the uncertainty is minimized in the comparison between observation and LES results. This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-648654