Gravity waves generated by deep tropical convection: Estimates from balloon observations and mesoscale simulations

Abstract

Convective gravity waves in the Tropics are studied by analyzing in situ measurements from long-duration stratospheric balloons launched during the PreConcordiasi campaign (2010) and mesoscale simulations. An improved temporal resolution of the observations as well as the balloon quasi-Lagrangian behavior allow an unprecedented investigation of the whole gravity wave spectrum. First, a case study of gravity waves generated by a developing cyclone, Tropical Storm Gelane (February 2010), is carried out using observations complemented by numerical simulations with the Weather Research and Forecast model, with a resolution down to 1 km. Distributions of momentum fluxes obtained from both data show reasonable agreement and emphasize waves with short wavelengths (<15 km) and short periods (<20 min). Still, some differences are also found, which can likely be related to errors of the modeled background flow. Second, observations from the whole PreConcordiasi flights are analyzed with an emphasis on gravity wave momentum fluxes. Their phase speed distribution has a robust shape, with maximum fluxes with near-zero ground-based phase speeds. Yet, significant momentum fluxes are also found for larger values, yielding a mean phase speed of about 27 ms -1. The momentum fluxes are concentrated in short episodes with intense values, and their intermittency is quantified using probability distribution functions and the Gini coefficient (0.5-0.6). The relative importance of convective and topographic sources are investigated, suggesting comparable intensities, but a greater occurrence frequency of convective events. Waves emitted by Tropical Storm Gelane do not stand out relative to other convective events. Key Points The whole gravity-wave spectrum is studiedin simulations and balloon data.Most momentum fluxes come from short-wavelength, short-period waves.Intermittency is quantified, a robust phase-speed distribution is found. ©2013. American Geophysical Union. All Rights Reserved.