Gravity waves generated by convection in the Darwin area during the Darwin area wave experiment

Abstract

We describe a model study of gravity wave generation by convection near Darwin during the Darwin Area Wave Experiment (DAWEX). We focus on an 7-hour period on 17 November 2001 for our study which included a major Hector event over the Tiwi Islands followed by a continental convective outbreak that included a squall line to the southeast of Darwin. Our model is a dry version of a three-dimensional (3-D) mesoscale cloud resolving model with horizontally uniform background wind and stability fields. The model is forced with a spatially and temporally varying heating field representative of the convective latent heating in the area. We derive this heating field from 3-D volumetric reflectivity from the precipitation radar located just north of Darwin at Gunn Point during DAWEX. The conversion from radar reflectivity to a 3-D latent heating field requires numerous assumptions that do not allow a quantitative heating estimate but which do provide a very realistic measure of the spatial morphology and temporal variations of the latent heating. Gravity waves generated by convective heating are known to be very sensitive to these characteristics of the heating, so our resulting wave field is likely to be the most realistic possible description of the waves emitted from convection in the Darwin area. Uncertainty in the wave amplitudes is large both because the input forcing (heating) is uncertain and because the use of heating as the sole proxy for wave forcing leads to additional wave amplitude errors. We therefore compare the results of the model to other DAWEX measurements and previous modeling studies both to validate the waves in our model and to calibrate the wave amplitudes. Our study in turn aids in the interpretation of the other gravity wave measurements during DAWEX. Copyright 2004 by the American Geophysical Union.