On the propagation and upscale development of explicity simulated convectively-coupled gravity waves

Results from several recent 2D CRM (two-dimensional cloud-resolving model) studies have shown that large-scale [O(1000 km)] convectively coupled gravity waves tend to "spontaneously" develop from random initial conditions. By spontaneous development, we mean that which occurs in the presence of uniform large-scale forcing and uniform lower boundary conditions. Two important questions raised by such findings are: 1) what determines the horizontal propagation speed of the waves, and 2) what are the mechanisms responsible for their upscale development.

In an effort to address these questions, we used a vertical mode transform algorithm to project the winds, temperature, and heating anomalies associated with the simulated waves onto the vertical modes of the model's base state atmosphere. The results of this analysis show that: 1) the propagation speed of the waves is set by interactions between convection and vertical modes with relatively short vertical wavelengths in the troposphere (~ 10 km), and 2) the upscale development of the waves is due to the successive generation of smaller-scale [O(50 km)] gravity wave disturbances towards the rear of the wave's convective envelope. Some possible explanations for this successive generation are discussed.