Case study analysis of convectively-generated gravity waves

Dr Jeffrey Chagnon
Dr Suzanne Gray

Viewed from the perspective of the larger scale environment, convection is a localised source of rapid heating and acceleration that generates gravity waves. These waves can have a significant impact on the surrounding environment, including the triggering or reorganisation of nearby convection, the establishment of mixing layers near the tropopause, and the maintenance of large scale circulation in the middle atmosphere. Simulating such waves is a challenge for mesoscale numerical models which do not resolve the full wave spectrum or its source unambiguously. This work examines the characteristics of convectively-generated gravity waves in several cases simulated using the mesoscale version of the Met Office Unified Model. We examine the dependence of simulated waves on model configuration (e.g., resolution and convective parameterization) as well as the thermodynamic and kinematic properties of the background environment. In order to clarify the model results, we also analyse radar observations from the MST radar facility in Aberystwyth and perform additional numerical experiments with an idealised linear model. Significant findings to date include the identification of multiple spectral peaks at horizontal scales below 50 km. These peaks might be attributable to either a parameteric (wave-wave) instability, or a resonant interaction between the waves and their source near the tropopause.

Related publications

Chagnon, J. M., and S. L. Gray, 2008: Analysis of convectively-generated gravity waves in mesoscale model simulations and wind profiler observations. The Quarterly Journal of the Royal Meteorological Society, 134, 663 - 676.