EFFECTS OF AN ATMOSPHERIC GRAVITY-WAVE ON THE MIDLATITUDE IONOSPHERIC F-LAYER

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 N(m)F2 and h(m)F2, 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, N(m)F2 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 h(m)F2 falls below its equilibrium value.