Effects of an atmospheric gravity wave on the midlatitude ionospheric F layer

Abstract

A modeling study of the atmospheric response to a single short burst of enhanced ion convection at high latitudes, undertaken using the Sheffield/University College London/Space Environment Laboratory coupled ionosphere/thermosphere model, has revealed a large‐scale atmospheric gravity wave (AGW) moving equatorward from a source in the dawn sector auroral zone. The wave propagates to midlatitudes, perturbing the ionosphere and creating a traveling ionospheric disturbance. Analysis of the interaction between the thermosphere and ionosphere during the passage of the AGW at midlatitudes is undertaken and reveals a complex height‐dependent response. At lower altitudes the field‐aligned velocity of the ions follows closely the field‐aligned wind. Above the F peak, diffusion processes become important and the field‐aligned ion velocity shows fluctuations which exceed those in the wind. Changes in NmF2 and hmF2, during the interaction, are due to redistribution of plasma alone with changes in production and loss insignificant. As the F layer is lifted by the positive surge in the gravity wave, NmF2 decreases, due to a divergence in the ion flux, itself caused by the combination of a divergent neutral wind and an increase in the effects of diffusion with altitude. The slab thickness also increases. Subsequently, the opposite happens as hmF2 falls below its equilibrium value.

Observations and modeling of the April 10–12, 1997 ionospheric storm at Millstone Hill

“…It has been shown, however, that gravity waves cause height variations in the neutral wind (wind shears), which extend into the topside ionosphere [Millward et al, 1993]. Gravity waves are assumed to play a crucial role in the redistribution of the ionospheric plasma during positive ionospheric storm effects of short duration (e.g.…”

A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

“…The duration of the electric ®eld enhancement was 10 min from 12.15 UT (23.03 LT). The magnitude, duration and extent of the enhanced electric ®eld was designed to simulate a typical burst' in the auroral ion velocity (Hajkowicz 1990;Millward et al, 1993a). The geographic location of the enhancement was chosen to ensure that the AGW propagated through the night ionosphere where the amplitudes of observed TIDs are largest (Hajkowicz, 1990).…”

A study of the Joule and Lorentz inputs in the production of atmospheric gravity waves in the upper thermosphere

“…The magnitude and duration of the enhanced electric ®eld was designed to simulate a typical`burst' in the auroral ion velocity (e.g. Millward et al, 1993a), whilst the extent was designed to cover a signi®cant fraction of the auroral region and to cover several`grid points' on the thermospheric grid to avoid resolution e ects; the choice of 6 by 5 grid points was arbitrary.…”

“…In the region of enhanced electric ®eld (the source region) it was found that ion-neutral frictional heating caused an expansion of the atmosphere, loss of plasma due to increased recombination rate and upward¯ow, and increased abundance of molecular ions. The initial expansion of the atmosphere was followed by a relaxation, leading to the formation of a large-scale AGW (Millward et al, 1993a). Here we see that both cases result in AGWs propagating principally meridionally from the source region.…”