Ionospheric signatures of particular magnetospheric configurations - ASAIDs
Mirela Voiculescu - Dunarea de Jos University of Galati, Romania
The magnetosphere-ionosphere coupling may result, in some cases, in strong westward ion flows (in excess of 1 km) observed in the ionospheric F region and in the top ionosphere, known as subauroral ion drifts (SAIDs). They have a narrow latitudinal extent and are located equatorward of the nightside auroral zone at geomagnetic latitudes of 50-65 degrees, lasting less than 3 hours. There are three main theories that explain SAIDs as a result of magnetospheric processes, which will be reviewed here.
We have identified, for the first time, strong eastward ion drifts, with speeds larger than 1 km/s, widths of 1-2 degrees and occurring at similar temporal and spatial locations as sub-auroral ion drifts. We have called them Abnormal Subauroral Ion Drifts, ASAIDs. They coincide with deep, narrow troughs in the total ion density both at the altitude of the F15 DMSP satellite (850 km) and in the F region of the ionosphere, but do not seem to be a feature of the convective transport. During the entire duration of ASAID the electron temperature is very high while, contrarily to SAID, the ion temperature has no clear variation. We show that the generator of ASAID could be located inside the plasmasphere close to the plasmapause. We suggest a possible mechanism of ASAID generation which requires a particular magnetospheric configuration, where hot ring current particles and cold particles of the outer plasmasphere overlap partially, creating an earthward electric field, mapping in the ionosphere as an equatorward electric field.
