Estimating entrainment and detrainment from individual clouds using large eddy simulations of shallow convection

Speaker: Phil Austin, UBC, Vancouver

When: Wednesday, April 16, 2014, 3:30 p.m. Mountain Time
Location: Room 2A305, DSRC (NOAA Building), 325 Broadway, Boulder
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We use high resolution simulations of shallow convection to directly estimate entrainment and detrainment rates of thousands of individual clouds tracked over their life-cycle. Our simulations allow us to map the impact of cloud and environmental properties (height above cloudbase, vertical velocity, critical mixing fraction, environmental lapse rate and buoyancy) on entrainment and detrainment rates of a passive tracer and vertical momentum. Paired correlations and measures of the mutual information point to the buoyancy and the environmental stability as the primary controls for entrainment, while vertical velocity and the critical mixing fraction control detrainment. These variable pairs also provide the best fit to the average direct entrainment and detrainment of the entire cloud field. We will look at the implications of these results for the question of "nature vs. nurture" (i.e. are cloud properties determined primarily by their state at initiation, or by their mixing) and the development of large-scale parameterizations of convective mixing.