Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm72b0618a&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM72B-0618
Physics
2407 Auroral Ionosphere (2704), 2409 Current Systems (2708), 2712 Electric Fields (2411), 2736 Magnetosphere/Ionosphere Interactions
Scientific paper
The solar EUV contribution to ionospheric conductivity should produce a diurnal variation in the Birkeland, Hall and Pedersen currents. The Iridium system of satellites provides nearly uniformly spaced coverage at all local times regardless of the time of day and simultaneous observations in northern and southern hemispheres allow separation of variations in the solar wind dynamo, both due to dipole tilt effects and solar wind/IMF dynamics, from those associated with hemispheric differences. We examine three years of Iridium magnetometer key parameters [Anderson et al., 2002] for seasonal and diurnal variations in the ratio of total Birkeland current flowing in the northern and southern hemispheres. The N/S FAC ratio is evaluated using three different measures of FAC intensity: maximum magnetic perturbation (95-100 percentile average), median magnetic perturbation (45-55 percentile average) and average fraction of samples above the noise level. All three measures show the same basic pattern. The seasonal and diurnal variations on the dayside are much larger than the nightside indicating that variations in solar illumination are responsible. Moreover, the N/S FAC ratio is in phase with the N/S average ionospheric conductance estimated using diurnal variation in magnetic coordinates, dominated by dipole tilt effects. The results imply a strong diurnal hemispherical anti-phase relationship in FACs and in associated Joule heating which should have important consequences for modeling high latitude thermospheric dynamics.
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