Physics
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995jatp...57..279b&link_type=abstract
Journal of Atmospheric and Terrestrial Physics (ISSN 0021-9169), vol. 57, no. 3, p. 279-292
Physics
15
Asymmetry, Atmospheric Ionization, Atmospheric Models, Earth Ionosphere, Equatorial Regions, Ionospheric Electron Density, Magnetohydrodynamic Flow, Annual Variations, Antipodes, Diurnal Variations, Ionospheric Drift, Nocturnal Variations, Solar Activity, Zonal Flow (Meteorology)
Scientific paper
The relative importance of the equatorial plasma fountain (caused by vertical E x B drift at the equator) and neutral winds in leading to the ionospheric variations at equatorial-anomaly latitudes, with particular emphasis on conjugate-hemisphere differences, is investigated using a plasmasphere model. Values of ionospheric electron content (IEC) and peak electron density (Nmax) computed at conjugate points in the magnetic latitude range 10-30 deg at longitude 158 deg W reproduce the observed seasonal, solar activity, and latitudinal variations of IEC and Nmax, including the conjugate-hemisphere differences. The model results show that the plasma fountain, in the absence of neutral winds, produces almost identical effects at conjugate points in all seasons; neutral winds cause conjugate-hemisphere differences by modulating the fountain and moving the ionospheres at the conjugate hemispheres to different altitudes. At equinox, the neutral winds, mainly the zonal wind, modulate the fountain to supply more ionization to the northern hemisphere during evening and night-time hours and, at the same time, cause smaller chemical loss in the southern hemisphere by raising the ionosphere. The gain of ionization through the reduction in chemical loss is greater than that supplied by the fountain and causes stronger premidnight enhancements in IEC and Nmax (with delayed peaks) in the southern hemisphere at all latitudes (10-30 deg). The same mechanism, but with the hemispheres of more flux and less chemical loss interchanged, causes stronger daytime IEC in the northern hemisphere at all latitudes. At solstice, the neutral winds, mainly the meriodional wind, modulate the fountain differently at different altitudes and latitudes with a general interhemispheric flow from the summer to the winter hemisphere at altitudes above the F-region peaks. The interhemispheric flow causes stronger premidnight enhancements in IEC and Nmax and stronger daytime Nmax in the winter hemisphere, especially at latitudes equatorward of the anomaly crest. The altitude and latitude distributions of the daytime plasma flows combined with the longer daytime period can cause stronger daytime IEC in the summer hemisphere at all latitudes.
Bailey Graham J.
Balan Nanan
Moffett R. J.
Su Zheng-Yao
Titheridge J. E.
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