5.3 Radiatively generated vortical flows

Wednesday, 10 June 2009: 8:40 AM
Pinnacle BC (Stoweflake Resort and Confernce Center)
Gregory J. Hakim, University of Washington, Seattle, WA

Subsynoptic-scale vortices are ubiquitous features of the arctic troposphere. Typical cyclonic vortices are cold-core, based on the tropopause, and may last more than one month. Such features are abundant year round, with an average of 15 unique vortices per month in winter and 12 in summer. Despite their ubiquity and longevity, the dynamics of these features remain poorly understood, particularly with respect to genesis. Here we explore the possibility that the vortices may be generated spontaneously by radiative cooling, using theoretical arguments and idealized numerical calculations.

We consider axisymmetric circulations generated from rest on a piecewise constant domain consisting of regions inside and outside the vortex. These domains are linked by a diagnostic equation for vertical motion forced by the radial gradient in diabatic heating. Accurate heating rates are determined by direct calculation using a column radiative transfer model (RRTM). An optimal stability approach is employed to determine perturbations that maximize circulation tendency, and a numerical model is used to determine finite-time behavior. The opposing tendency from latent heating will also be discussed.

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