The southern hemisphere ionosphere and plasmasphere response to the interplanetary shock event of 29 - 31 October 2003

We analyze the effects on the southern hemisphere ionosphere and plasmasphere of the geomagnetic storms occurring in the interval 29-31 October 2003 (the so called series of Halloween storms). Solar wind data from ACE and ionospheric data from: GPS ground and LEO receivers; the TOPEX/Poseidon altimeter; the IMAGE FUV camera, and the DMSP drift meter, are used to understand the ionospheric dynamics as a function of the storm phase. The detailed structure of the ionosphere has been obtained using tomographic reconstruction applied to data from both ground and space based GPS receivers. The tomographic approach using LEO observations of signals received from GPS satellites above the LEO's horizon allows us to investigate the topside ionospheric and plasmaspheric density distribution in more detail than can be obtained using ground based GPS receivers. This is because with ground based receivers, the higher topside ionosphere and plasmasphere contribute only a small fraction to the total electron content (TEC) and so the measurements are dominated by the ionospheric structure at the F2 peak. In contrast the Australian LEO satellite, FedSat, which has been used for this study, orbits at 800 km altitude, well above the F2 peak and hence the TEC measured is primarily due to the upper topside ionosphere and plasmasphere. In this paper we present tomographically reconstructed topside ionosphere and plasmasphere electron density distributions for the above mentioned severe magnetic storm period. The results we report here, the tomographically reconstructed topside ionosphere and plasmasphere electron density distributions, are the first of such LEO observations. The temporal and regional maps of TEC and the IMAGE FUV data show that the first storm that commenced on 29 October dramatically decreased the density in the southern hemisphere mid- and high-latitudes. The region remained depleted of density for more than 24 hours until 31 October, when the second severe storm began. From TOPEX/Poseidon data, a daytime localized density enhancement occurred above the middle of the Pacific Ocean. An eastward expanding trough-like structure, crossing middle Australia, is another important feature that was observed.