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

A time‐dependent, nonlinear, fully compressible, axisymmetric, ƒ‐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.