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

Abstract

Abstract.A global coupled thermosphere-ionosphereplasmasphere model is used to simulate a family of large-scale imperfectly ducted atmospheric gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) 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 identi®ed. We ®nd that, at the magnetic equator, all the clearly identi®ed modes of AGW interfere constructively and pass through to the opposite hemisphere with unchanged velocity. At F-region altitudes the`fast' AGW has the largest amplitude, and when northward propagating and southward propagating modes interfere at the equator, the TID (as parameterised by the fractional change in the electron density at the F2 peak) increases 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 AGWs ®rst interfere, and it is suggested that this is due to enhancements of the TID by slower AGW modes arriving later at the magnetic equator. The complex e ects of the interplays of the TIDs generated in the equatorial plasmasphere are analysed by examining neutral and ion winds predicted by the model, and are demonstrated to be consequences of the forcing of the plasmasphere along the magnetic ®eld lines by the neutral air pressure wave.

Magnetic storm-induced enhancement in neutral composition at low latitudes as inferred by O(<sup>1</sup>D) dayglow measurements from Chile

“…From satellite measurements it is known that neutral densities increase in low latitudes during geomagnetic storms (for example, Hedin et al, 1977;Mayr et al, 1978;Burrage et al, 1992;Prolss, 1993;Burns et al, 1995). This redistribution is caused by transport of the neutrals (Mayr et al, 1978;Prolss, 1980) from the hot polar latitudes to the colder low and equatorial latitudes and by TADs (Prolss, 1993;Fujiwara et al, 1996;Balthazor and Moffet, 1997). An essential feature of such a TAD is that it carries equatorward-directed winds along with it.…”

“…The wind strengths also increase with an increase in the intensity and the duration of the magnetic storm. Furthermore, TADs generated during magnetic storms propagate with high velocities from the polar to the equatorial-latitudes, and depending on their strength, they are also capable of propagating to the opposite hemisphere (Fujiwara et al, 1996;Balthazor and Moffet, 1997). There is a good temporal correlation between the magnetic storm activity at high latitudes and the increase in neutral gas densities at low latitudes (Prolss, 1993;Fujiwara et al, 1996;Balthazor and Moffet, 1997).…”

“…Also, variabilities in the columnintegrated emissions can be brought about by changes in the neutral composition due to the transport from the high latitudes, propagation of the gravity waves, neutral winds, etc. (Fujiwara et al, 1996;Balthazor and Moffet, 1997). Notice the periodicities of small-amplitude oscillations, which seem to increase in time periods from around 30 min in the morning to around 100 min in the evening.…”

Ionosphere Waves Service (IWS) – a problem-oriented tool in ionosphere and Space Weather research produced by POPDAT project

“…TIDs propagate in global scales from auroral ovals toward low latitudes (Balthazor & Mofett 1997) and/or across polar caps (Cai et al 2011) appearing as oscillations in F-region plasma parameters, like plasma density, temperature, drift velocity, mean ion mass, etc. These oscillations provide significant fluctuations in the plasma parameters registered by in situ observations at low Earth orbiting satellites and/or remotely by various ground-based radio-sounding techniques; between these possibilities one of the most effective technique is the measuring of the total electron content (TEC) along the GPS signal propagating path crossing the whole ionosphere (Crespon 2007).…”

Tsunami Detection by Ionospheric Sounding: New Tools for Oceanic Monitoring

“…Moreover, a period between 22 and 33 min, consistent with the tsunami, was identified in the observed TEC signals. The tsunami generated internal gravity waves (IGWs) were, however, superimposed by other signals associated with traveling ionospheric disturbances (TIDs) (Balthazor & Moffett, 1997). The ionospheric noise is large in the gravity domain (Garcia et al, 2005), consequently the identification of the tsunami signature in the TEC could be doubtful, and the debate still open.…”