Small-scale gravity waves in the upper mesosphere and lower thermosphere generated by deep tropical convection

A time-dependent, nonlinear, fully compressible, axisymmetric, f-plane, numerical model is used to simulate the generation of small-scale gravity waves in the upper mesosphere and lower thermosphere by intense deep convection in the troposphere. The simulations show that major convective storms in the tropics excite a broad spectrum of upper mesosphere-lower thermosphere gravity waves above the storm centers. The wave field includes a component that is guided in a thermal duct in the lower thermosphere and propagates horizontally outward from above the storm. Storms excite oscillations over the source which are initially confined to a stratospheric duct but leak into the thermospheric duct over time, generating a long train of small-scale-ducted waves. This ringing phenomenon persists for several hours after the storm has ended. The ducted disturbances may propagate large distances from the source and explain observations of a strong summertime anisotropy favoring southward propagation of small-scale waves observed in the airglow over Adelaide more than 2000 km to the south of the storm events. (Author)