Moderate- to large-amplitude mesoscale gravity waves (MGWs) have been the topic of study for many years. Though usually accompanied by precipitation bands that may be tracked with surface-based radar, their detailed structure has been best documented with observations collected during field experiments. At the same time, numerical modeling has emerged as a powerful tool with which to study wave genesis, maintenance and decay.

The recent observational and modeling study of the 14 February 1992 MGW event during STORM-FEST revealed an important role for precipitation bands aloft in wave genesis (Rauber et al. 2001, Yang et al. 2001, and Jewett et al. 2003). Evaporative cooling and subsequent downdraft formation above a low-level stable layer was essential for wave genesis in the STORM-FEST case. While real-data MM5 experiments with and without key physical processes isolated the role of evaporative cooling in this case, the genesis mechanism has not yet been generalized to assess the impact of cooling rates and structure aloft and low- and mid-tropospheric lapse rates on the details of wave genesis and evolution.

Numerical simulations with the WRF model are being carried out to study wave genesis in dry, idealized environments with specified cooling aloft. This work is designed to improve our understanding of the evaporative cooling mechanism of wave genesis and the parameter space under which the mechanism can produce a significant mesoscale gravity wave. Early tests revealed that highly correlated surface wind and pressure perturbations formed when downdrafts aloft impinged on a low-level inversion. The surface evidence of wave presence persisted, suggesting the importance of evaporation to the rear of rainbands as a maintenance mechanism for mesoscale gravity waves in real-world cases.