Convectively-coupled gravity wave disturbances in the Tropics

Tropical deep convection has long been known to interact strongly with large-scale atmospheric wave circulations -- well known examples include convectively coupled Kelvin waves and the Madden-Julian Oscillation, both of which have characteristic spatial scales measured in 1000s of kilometers. In addition to these synoptic scale waves, however, we present evidence for zonally-propagating inertio-gravity gravity wave disturbances with spatial scales typically on the order of 100s of kilometers and frequencies < 2.5 day. These short/fast waves are shown to be strongly tied to the diurnal cycle over land, and to appear prominently near certain geographic features, such as the eastern mountains of Rwanda, the central mountains of New Guinea, and the northeastern coast of Brazil. We also provide evidence that some of these disturbances may be involved in the genesis of tropical storms, such as Hurricane Andrew 1992.

A number of open questions currently surround the existence of these high-frequency wave modes. First and foremost is the question of what determines their relatively shallow equivalent depths (~25 m; comparable to that of lower-frequency Kelvin modes)? Another question concerns a dramatic bias in the propagation direction of the waves, with westward-moving waves appearing more prominently than eastward-moving. As a first step towards addressing these issues, we use radiosonde and reanalysis data to examine the dynamical structures of the waves, as well as their background environments.