13.3 Comparison of the analytical and numerical model for convectively coupled gravity waves

Friday, 12 June 2009: 8:40 AM
Pinnacle BC (Stoweflake Resort and Confernce Center)
Zeljka Fuchs, University of Split, Split, Croatia; and S. L. Sessions and D. J. Raymond

The analytical model by Raymond and Fuchs (2008) is a linearized, two-dimensional, non-rotating model of the tropical atmosphere. It incorporates the saturation fraction of the troposphere, surface moist entropy fluxes, and the strength of convective inhibition into its convective closure. A modeled convectively coupled gravity mode, that maps onto equatorial Kelvin waves in the earth's atmosphere, is governed by anomalies in convective inhibition caused by buoyancy variations just above the top of the planetary boundary layer. The model is vertically resolved, the vertical structure of computed temperature matches the observations and so does the phase speed of 17 m/s. The phase speed of the convectively coupled gravity mode is a dynamical property of the wave itself as it does not depend on various convective closures.

In a series of experiments using a cloud resolving model in two-dimensional domain (7000 km in the horizontal, horizontal grid spacing 1 km and 2 km) large-scale waves with phase speed of 15 m/s developed. All simulations were run for 15 days. The analysis of the produced wave shows that it matches a convectively coupled gravity mode, but an interesting point is that among many parameters (humidity, CAPE) it showed the strongest correlation with convective inhibition.

Crucial to the hypothesis for convectively coupled gravity waves in the analytical model is that the convection is largely controlled by the capping layer. The numerical runs show the very same thing.

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