4.2 Mixed-phase clouds: from theory to application in a global model

Monday, 7 July 2014: 3:45 PM
Essex Center/South (Westin Copley Place)
Kalli Furtado, Met Office, Exeter, United Kingdom; and P. Field, A. Hill, B. Shipway, and A. Korolev

A lack of liquid water in mixed-phase clouds has been implicated as a possible cause of model outgoing short-wave biases, and associated SST biases, over the Southern Ocean. A physically based method for parametrizing the role of sub-grid scale turbulence in the production and maintenance of supercooled liquid water in mixed-phase clouds is presented. The approach used is to simplify the dynamics of supersaturation fluctuations to a stochastic differential equation that can be solved analytically to provide expressions for the mixed-phase cloud fraction and mean liquid water content. We demonstrate that the approach captures the properties of decameter-resolution Large Eddy Simulations of a turbulent mixed-phase environment and show how it can be implemented in a GCM and the effects that this has on Southern Ocean biases and on Arctic stratus.
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