Numerical modeling of gravity wave generation by deep tropical convection

Although convective clouds are known to generate internal gravity waves, th e mechanisms responsible are not well understood. The present study seeks t o clarify the dynamics of wave generation using a high-resolution numerical model of deep convection over the Tiwi Islands, Australia. The numerical c alculations presented explicitly resolve both the mesoscale convective clou d cluster and the gravity waves generated. As the convective clouds evolve, they excite gravity waves, which are prominent features of the model solut ions in both the troposphere and stratosphere. The source location is varia ble in time and space but is related to the development of individual conve ctive cells. The largest amplitude gravity waves are generated when the clo ud tops reach the upper troposphere. A new analysis technique is introduced in which the nonlinear terms in the governing equations are taken as the forcing for linear gravity waves. The analysis shows that in the present calculation, neither the shear nor the d iabatic heating are the dominant forcing terms. Instead, the wave source is most easily understood when viewed in a frame of reference moving with the wind at the level of neutral buoyancy, whereupon the source may be describ ed as a vertically oriented, oscillating convective updraft. This descripti on is consistent with the properties of the modeled stratospheric waves.