3.2 Under what conditions does embedded convection enhance orographic precipitation?

Monday, 30 August 2010: 1:45 PM
Alpine Ballroom A (Resort at Squaw Creek)
Dirk Cannon, University of Reading, Reading, Berkshire, United Kingdom; and D. J. Kirshbaum

Although convective orographic clouds generally produce larger local precipitation rates than stable laminar clouds, the impact of this convection on area-averaged precipitation amounts, and hence the large-scale flow, is still not fully understood. To improve this understanding, we conduct a large number of idealised, cloud-resolving numerical simulations of moist flow over Gaussian orography. A wide range of parameter space is considered to capture the dominant environmental and terrain-related controls on convective vigor, condensation amounts, and precipitation efficiency. The results suggest that embedded convection only yields a significant precipitation enhancement in certain well-defined regions of parameter space. This behavior can be qualitatively explained through a consideration of the relevant advective, convective, and microphysical timescales. More quantitative insight is provided through a simple scaling analysis of orographic precipitation that is valid for both stratiform and convective orographic clouds.
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