Low Latitude Gravity Wave Variances in the MLT Derived from Saber Temperature Observation and Compared with Model Simulations of Waves Generated By Deep Tropical Convection

Abstract:

Equatorial regions are the scene of prolific generation of gravity waves by deep tropical convection. Waves generated by deep convection have appreciable energy at frequencies and spatial scales that are able to reach altitudes in the Middle Atmosphere and Lower Thermosphere (MLT) and above where they may attain significant amplitudes. A portion of these waves have scales and amplitudes large enough to be detected by space borne instruments. We have analyzed temperature data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite for sub-tidal scale fluctuations. Filtering was applied both vertically and horizontally to extract wave variances. We have examined the variances at equatorial latitudes for the altitude region between 70 and 120 km and have have characterized them as a function of season, local time intervals, geographical location and altitude. We find large variances in locations of where convection is particularly prolific (e.g., western South Pacific) and at altitudes where wave trapping is known to be favored (e.g., the lower thermospheric duct). The locations of significant variances persist from year to year. Variances of on the order of a few tens of degrees are found. We have also performed simulations of the response to deep tropical convection with the The Aerospace Corporation Dynamical Model (ADM). This model is a time dependent, high-resolution fully compressible dynamical model that has been used to examine the MLT wave response to intense cellular convection in northern Australia. The background thermal structure for the present simulations was obtained from TIMED/SABER data averaged over low latitudes by season and local time. Our simulations give wave amplitudes that agree reasonably well with the observed amplitudes and show layering that is consistent with the observations. We will show the results of our analysis of TIMED/SABER temperature as a function of geographical location (maps) and altitude (height-latitude cross-sections) for various seasons and local times. We will show simulations for various background thermal states. Our main finding is that in large part significant point to point variations seen in TIMED/SABER temperature data have a wave source.