13th Conference on Mesoscale Processes


Mesoscale Radiatively-Induced Anvil Spreading

Steven K. Krueger, University of Utah, Salt Lake City, UT; and M. A. Zulauf

In idealized 2D simulations, we represented the generation of optically thick anvil clouds by adding (“injecting”) cloud ice in a layer over a time period of a few hours. We found that (1) there is no spreading without radiative heating, (2) mesoscale motions are required for spreading but cloud-scale motions and/or turbulence are not, and (3) solar radiation does not reduce the spreading. More realistic full life-cycle simulations support the conclusions reached with the injected anvil simulations.

In all the simulations, the spatial gradients of radiative heating at the anvil cloud edges produce a mesoscale circulation that spreads the anvil cloud outward at a significant rate (about 1 m/s). We call this mesoscale radiatively-induced anvil spreading (MRAS). As the cloud spreads due to the mesoscale circulation, the radiative heating gradients also spread. The result is a positive feedback that lasts as long as there is sufficient cloud ice. As a result of the radiatively-induced anvil spreading, the simulated anvils have greater infrared (IR) warming (greenhouse) effects than they would have without the radiatively-induced anvil spreading. This is due to both the greater spatial extent and the longer lifetimes of the radiatively interactive anvils.

Session 4, Mesoscale precipitation systems IV
Monday, 17 August 2009, 4:00 PM-5:00 PM, The Canyons

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