Abstract
First results of a modelling study of atmospheric gravity waves (AGWs) are presented. A fully-coupled global thermosphere-ionosphere-plasmasphere model is used to examine the relative importance of Lorentz forcing and Joule heating in the generation of AGWs. It is found that Joule heating is the dominant component above 110km. The effects of the direction of the Lorentz forcing component on the subsequent propagation of the AGW are also addressed. It is found that enhancement of zonal EÃB forcing results in AGWs at F-region altitudes of similar magnitudes travelling from the region of forcing in both poleward and equatorward directions, whilst enhancement of equatorward meridional EÃB forcing results in AGWs travelling both poleward and equatorward, but with the magnitude of the poleward wave severely attenuated compared with the equatorward wave
Highlights
The production and propagation mechanisms of atmospheric gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) have been studied in great detail; reviews have been written by e.g. Hines (1960), Hines (1974), Francis (1975), Richmond (1978), Hunsucker (1982) and most recently by Jing and Hunsucker (1993)
Observed characteristics more commonly used in AGW studies such as temperatures and winds are secondary eects of the pressure wave travelling through the thermosphere, whereas the change in height of a ®xed pressure level is a moredirect' measure of the wave
It is speculated that the high velocity ion drift. These ®rst results from the coupled thermosphereionosphere-plasmasphere model suggest that an enhancement in the auroral electric ®eld produces signi®cant AGW propagation at F-region altitudes
Summary
The production and propagation mechanisms of atmospheric gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) have been studied in great detail; reviews have been written by e.g. Hines (1960), Hines (1974), Francis (1975), Richmond (1978), Hunsucker (1982) and most recently by Jing and Hunsucker (1993). Brekke (1979) used height-dependent values of j and r, re-applying them to the equation of Chimonas and Hines (1970), to yield r. The approach is similar to that of Chimonas and Hines (1970) the source perturbation used was an enhancement in the electron density at E-region altitudes, yielding an expression for vat of v t. Magnetometer data was used to obtain the height-integrated current density j whilst Hall and Pedersen conductivity observations (Brekke et al, 1974) were used to calculate more precise values for the Cowling conductivity. Jing and Hunsucker (1993) presented an analytical solution to take into account density, pressure and velocity perturbations, the simpli®cations of an ideal windless isothermal atmosphere ignoring Coriolis eects are retained.
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