Neutral Winds and Densities at the Bottomside of the F Layer from Primary and Secondary Gravity Waves from Deep Convection

Abstract

We model the primary gravity waves (GWs) excited by overshooting convective plumes in a $20^{\circ}\times 20^{\circ}$ region in central Brazil for 6 h during the evening on 01 October, 2005. We ray trace these GWs into the thermosphere. At $z=250$ km (near the bottomside of the F layer), the surviving GWs have horizontal wavelengths of $\lambda_{\textrm{H}}\sim 200{-}300$ km, horizontal velocity amplitudes of $u',v'\le15\, \textrm{m/s}$, and neutral density perturbations of $\rho'/\,\overline{\rho} \le2$%. We compute the thermospheric body forces, and input them into the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). These forces create a “mean” eastward wind perturbation at $z\sim150$ km of $200{-}340\; \textrm{m/s}$ which lasts for ∼3 h. These forces also excite large-scale secondary GWs in all directions for at least 3 h with horizontal wavelengths of $\lambda_{\textrm{H}}\sim4000{-}5000$ km, horizontal phase speeds of $c_{\textrm{H}}\sim500{-}600\;\textrm{m/s}$, and density perturbations of 5–15% at $z=250$ km. Prior to and after sunset, the wind perturbations are eastward with $u'\sim75{-}150\;\textrm{m/s}$ at $z=250$ km. This occurs over the convective region, where the winds from 2 large vortices (created by the forces) converge. In other areas, the winds are west, south, or northward. It is likely that these forces (and the GWs they excite) significantly affect the F region dynamo and the seeding of equatorial plasma bubbles (EPBs).