A STUDY OF ATMOSPHERIC GRAVITY-WAVES AND TRAVELING IONOSPHERIC DISTURBANCES AT EQUATORIAL LATITUDES

A global coupled thermosphere-ionosphere-plasmasphere model is used to simulate a family of large-scale imperfectly ducted atmospheric gravi ty waves (AGWs) and associated travelling ionospheric disturbances (TI Ds) originating at conjugate magnetic latitudes in the north and south auroral zones and subsequently propagating meridionally to equatorial latitudes. A 'fast' dominant mode and two slower modes are identified . We find that, at the magnetic equator, all the clearly identified mo des of AGW interfere constructively and pass through to the opposite h emisphere with unchanged velocity. At F-region altitudes the 'fast' AG W has the largest amplitude, and when northward propagating and southw ard propagating modes interfere at the equator, the TID (as parameteri sed by the fractional change in the electron density at the F2 peak) i ncreases in magnitude at the equator. The amplitude of the TID at the magnetic equator is increased compared to mid-latitudes in both upper and lower F-regions with a larger increase in the upper F-region. The ionospheric disturbance at the equator persists in the upper F-region for about 1 hour and in the lower F-region for 2.5 hours after the AGW s first interfere, and it is suggested that this is due to enhancement s of the TID by slower AGW modes arriving later at the magnetic equato r. The complex effects of the interplays of the TIDs generated in the equatorial plasmasphere are analysed by examining neutral and ion wind s predicted by the model, and are demonstrated to be consequences of t he forcing of the plasmasphere along the magnetic field lines by the n eutral air pressure wave.