Generation of large-scale gravity waves and neutral winds in the thermosphere from the dissipation of convectively generated gravity waves

摘要

We study the response of the thermosphere and ionosphere to the dissipation of gravity waves (GWs) excited by a deep convective plume on 1 October 2005 at 52.5°W, 15.0°S, and 2120 UT in Brazil. Those small- and medium-scale GWs which reach the thermosphere dissipate at z 120-250 km in a direction opposite to the background wind —(1-2) density scale heights below. This localized momentum deposition creates horizontal thermospheric body forces that have large sizes and amplitudes and generates large-scale secondary GWs and large-scale traveling ionospheric disturbances (LSTIDs) that propagate globally away from the body force in all directions except that perpendicular to the force direction. For the convective plume at 2120 UT, the secondary GWs have horizontal wavelengths of AH 2100-2200 km, periods of Tr ^, 80 min, horizontal phase speeds of CH — 480-510 m/s, density perturbations as large as Ip'/p1 — 3.6-5% at z = 400 km, relative [0] perturbations as large as —2-2.5% at z = 300 km, and total electron content perturbations as large as —8%. This transfer of momentum from local, relatively slow, small scales at the tropopause to global, fast, large scales in the thermosphere is independent of geomagnetic conditions. The various characteristics of these large-scale waves may explain observations of LSTIDs at magnetically quiet times. We also find that this body force creates a localized "mean" horizontal wind in the direction of the body force. For the plume at 2120 UT, the wind is southward with an estimated maximum of Vmax r —400 m s-1 that is dissipated after N4 h. We also find that the induced body force direction varies throughout the day, depending on the winds in the lower thermosphere.