Ion temperature troughs in the equatorial topside ionosphere
Abstract
The Retarding Potential Analyzer aboard OGO-6 sometimes recorded marked depressions of ion temperature as the satellite crossed the equatorial region. These " Ti troughs" occur at heights between about 700 km and the satellite apogee at 1100 km. At the centre of a trough, close to the dip equator, Ti is frequently 500-1000 K below its value at the northern and southern edges, which are usually 15°-20° in latitude from the centre of the trough. At a given season and local time, the occurrence, symmetry, depth and position of the troughs often vary markedly with longitude. The troughs have no particular association with equatorial troughs of ion concentration Ni. As suggested by Hanson, Nagy and Moffett, the Ti troughs appear to be caused by transequatorial winds that drive F region plasma along geomagnetic field lines. The plasma is adiabatically cooled as it is driven upwards on the "upwind" side of the dip equator, and heated as it descends on the "downwind" side. The available data on the occurrence of troughs at different longitudes, local times and seasons are reasonably consistent with wind directions deduced from Jacchia's model and the OGO-6 thermospheric model of Hedin et al., and with the north-south asymmetries of the tropical 630 nm airglow observed by OGO-4 and OGO-6. Factors determining the latitudinal extent of the troughs are discussed and some questions for further study are listed.
- Publication:
-
Planetary and Space Science
- Pub Date:
- July 1977
- DOI:
- 10.1016/0032-0633(77)90102-7
- Bibcode:
- 1977P&SS...25..629R
- Keywords:
-
- Ion Temperature;
- Ogo-6;
- Tropical Meteorology;
- Upper Ionosphere;
- Atmospheric Models;
- F Region;
- Longitude;
- Magnetic Equator;
- Night Sky;
- Plasma Dynamics;
- Satellite Observation;
- Satellite-Borne Instruments;
- Geophysics