The Effects of Local Body Forces and Re-Radiated Gravity Waves in the Mesosphere and Lower Thermosphere

* Use airglow and radar observations to further quantify MLT body forces

* Model the generation of secondary waves from these body forces, and ray-trace them into the lower thermosphere

* Determine the variability and mean horizontal accerlerations associated with the dissipation of the secondary waves in the lower thermosphere

* Put together a seasonal, global, zonally-averaged model of the subsequent effect of these high frequency waves on the lower thermosphere

Activities to date towards achieving these goals:

* Derived a simple dispersion relation for ray tracing gravity waves under the presence of molecular viscosity and thermal conductivity. A nice theoretical limit is obtained when the Prantl number is one (equal influences from molecular viscosity and thermal conductivity), and a simple analytical solution results. This solution yields some meaningful results, eg. that the height to which an internal gravity wave propagates depends sensitively on the value of the viscosity and is not an integrated effect. In addition, larger thermospheric temperatures than what we have modelled to date (273K) should allow MCC gravity waves to propagate 50-100km higher into the thermosphere than was previously found of z=210km. Upon dissipation, these gravity waves accelerate the background wind, thereby causing localized body forces spatially and temporally. This transfer of energy and momentum from the equatorial troposphere to the thermosphere can be important in seeding equatorial spread F.

* Studied the propagation of MCC (mesoscale convective complexes) gravity waves into the thermosphere using our 3D ray-tracing code which includes molecular viscosity (and will soon include thermal conductivity). However, the background thermal structure was assumed to be isothermal, which limits the height to which these gravity waves dissipate.

Publications under this grant to date:

* Sharon L. Vadas and David C. Fritts, 2004: "Thermospheric responses to gravity waves: Influences of increasing viscosity and thermal diffusivity", J. Geoph. Res., submitted.

* Sharon L. Vadas and David C. Fritts, 2004: "Thermospheric responses to gravity waves arising from mesoscale convective complexes", J. Atmos. Terr. Sci., 66, 781-804. Pdf version of this paper

* Sharon L. Vadas and David C. Fritts, 2004: "Thermospheric responses to gravity waves: Influences of increasing viscosity and thermal diffusivity", JGR, to be submitted.

This research was supported in part by the National Science Foundation under grant ATM-0307910.