Observation estimates of detrainment and entrainment in non-precipitating shallow cumulus
Norgren, M. S.
Small, J. D.
Jonsson, H. H.
Chuang, P. Y.
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Vertical transport associated with cumulus clouds is important to the redistribution of gases, particles and energy, with subsequent consequences for many aspects of the climate system. Previous studies have suggested that detrainment from clouds can be comparable to the updraft mass flux, and thus represents an important contribution to vertical transport. In this study, we describe a new method to deduce the amounts of gross detrainment and entrainment experienced by non-precipitating cumulus cloud using aircraft observations. The method utilizes equations for three conserved variables: cloud mass, total water, and moist static energy. Optimizing these three equations leads to estimates of the mass fractions of adiabatic mixed-layer air, entrained air and detrained air that the sampled cloud has experienced. The method is applied to six flights of the CIRPAS Twin Otter during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) which took place in the Houston, Texas region during the summer of 2006 during which 176 small, non-precipitating cumulus were sampled. Our analysis suggests that, on average, these clouds were comprised of 30 to 70% mixed-layer air with entrained air comprising most of the remainder. The mass fraction of detrained air was less than 2% for a majority of the clouds, although 15% of them did exhibit detrained air fractions larger than 10%. Entrained and detrained air mass fraction both increased with altitude, and the largest detrainment events were almost al associated with air that was at their level of neutral buoyancy, findings that are consistent with previous studies.
Approved for public release; distribution is unlimitedThis documnent marked "Discussion Paper". The article of record as published may be located at http://www.doi:10.5194/acpd-14-21785-2014Discussion Paper
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