Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm42a0592a&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM42A-0592
Physics
2708 Current Systems (2409), 2736 Magnetosphere/Ionosphere Interactions
Scientific paper
The Iridium system key parameters are used to compare the magnetic perturbations in the northern and southern hemisphere simultaneously. By using simultaneous data from the north and south the variations in currents due to changes in the solar wind-magnetosphere drivers of current are greatly reduced revealing true hemispherical differences for identical driving conditions. Three full years of data are used to characterize the seasonal and diurnal dependence of FACs. Strong seasonal and diurnal variations in the relative intensity of the Birkeland currents are found on the dayside and much smaller effects on the nightside. In a given hemisphere the net current is a factor of 1.6 larger in summer than in winter. The diurnal variation is nearly as large and the amplitude of the diurnal variation changes with season having the largest amplitude near the equinoxes. Both the seasonal and diurnal variations are modeled by comparing the relative ionospheric conductances modeled as the combination of solar EUV and particle contributions evaluated using empirical relations between solar zenith angle and conductivity and average Polar UVI auroral emission distributions. The observations can all be accounted for in terms of EUV and auroral conductances if the maximum auroral conductivity is near 10 mhos. In addition to the variations there is a persistent bias toward the northern hemisphere. After removing seasonal and diurnal effects, the magnetic perturbations are consistently 15 percent larger in the northern hemisphere than in the south. The uncertainty in the bias is less than 2 percent. The bias can be attributed to the combined effects of auroral zone geometry and magnetic field between the northern and southern hemispheres.
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