A three-dimensional mesoscale model is used to study the structure of convectively triggered gravity waves in the tropics, and their role in the dynamics of the middle atmosphere. The initial tropospheric thermodynamic sounding for the simulations is taken to be representative of the environment over Bathurst and Melville islands during a monsoon break period and before a ``Hector'' event (Keenan and Carbone 1991). The background tropospheric wind profiles are representative of the climatology of the monsoon break period for that region. Three stratospheric background zonal wind cases are examined. In the first case the background winds are constant, the other two are representative of the easterly and westerly phases of the quasi-biennial oscillation (QBO).
In all three cases, the triggered gravity wave field shows a strong horizontal isotropy below the critical levels, in the sense that the phase lines form circular patterns on a constant height surface. Spectral analysis is done and a peak in zonal wavelength and frequency are found at ~40km and ~30min., respectively, corresponding to a vertical wavelength of 8km.. This characteristic vertical wavelength is consistent with the vertical scale of latent heating.
In the QBO wind shear cases, upward propagating gravity waves are effectively damped as they approach their critical layer. The momentum flux convergence associated with critical layer absorption will tend partly to propagate the QBO shear layers downwards and partly to establish a zonal pressure gradient across the entire domain. Quantitative analysis of the stratospheric dynamical response to gravity wave momentum flux convergence will help asses the role of these waves in the forcing of the QBO's.
Close window or click on previous window to return to the Conference Program.
12th Conference on Atmospheric and Oceanic Fluid Dynamics