A Method for Realistic Simulation of Tropical Gravity Waves with Potential for near Real-Time Applications

Convective gravity waves (GWs) in the tropics are important for the correct simulation of the tropical Quasi-Biennial Oscillation (QBO) as well as the Semi-Annual Oscillation (SAO). The simulation of these waves requires cloud-resolving full-physics models. However, the application of these models is currently limited in two ways: first by the inaccurate representation of the locations, timing and intensity of individual convective cells and second by high computational costs.

Here, we present a new method suitable for rapid simulation of realistic GWs emanating from tropical convection, including both developing and more mature storm conditions. Our method is based on Stephan & Alexander (2015) who trained an algorithm using non-linear, full-physics cloud resolving model simulations to characterize the profile of latent heating using a single parameter, the near-surface rain rate. Their method found success in realistic representation of the characteristics of observed wave fields surrounding convective rain in mature midlatitude summertime storm conditions over the Continental US using rain-rates from ground-based scanning radar.

In this work, we associate the profile of latent heating with two parameters: rain rate and echo-top height. An ensemble of full-physics cloud-resolving WRF simulations is used to develop a lookup table for converting instantaneous radar precipitation rates and echo top measurements near Darwin, Australia, into a high-resolution latent heating field. The heating field from these simulations is then used to force an idealized dry version of the WRF model. Furthermore we present validation of the precipitation rates and clouds with scanning radar observations near Darwin and compare the resulting GW field of the idealized simulations with AIRS (Atmospheric InfraRed Sounder) satellite measurements. We demonstrate in this study that including the echo-top height variable leads to a dramatic improvement especially in the representation of amplitudes of the tropical convective GWs.

References

Stephan, C., & Alexander, M. J. 2015. Realistic simulations of atmospheric gravity waves over the continental U.S. using precipitation radar data. Journal of Advances in Modeling Earth Systems, 7(2), 823-835.