Displacement and changes in distribution of Birkeland currents during disturbed conditions relative to nominal activity

Details Displacement and changes in distribution of Birkeland currents during disturbed conditions relative to nominal activity Displacement and changes in distribution of Birkeland currents during disturbed conditions relative to nominal activity

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsa24a..04a&link_type=abstract

American Geophysical Union, Spring Meeting 2009, abstract #SA24A-04

Statistics

2704 Auroral Phenomena (2407), 2721 Field-Aligned Currents And Current Systems (2409), 2736 Magnetosphere/Ionosphere Interactions (2431), 2788 Magnetic Storms And Substorms (7954)

Scientific paper

Although much is known about the distributions of Birkeland currents and their relationship to ionospheric conductance and convection during periods of nominal activity, relatively little is understood about their expansion and configuration during storm times. This is largely because unlike convection which can be detected remotely via Doppler shifts in HF frequencies and conductance distributions which can be inferred either from coherent radars or auroral emissions, the field aligned currents cannot be sensed remotely but can only be measured in-situ by transiting the currents while measuring the corresponding magnetic field signatures of the currents. Individual satellite observations have provided a wealth of information about Birkeland currents in excellent statistical analyses, but these approaches are less enlightening when applied to storms both because of limited statistics and because the statistical approach may have limited applicability to active conditions. We therefore use the magnetometer data from the Iridium constellation of more than 70 satellites in low altitude, circular, polar orbits to assess the Birkeland currents during active conditions. These data, acquired for scientific use since February 1999, allow determination of the two-dimensional distribution and intensity of Birkeland currents with a few degree resolution in latitude from about one hour of observations. While not short enough to resolve many storm-time dynamics, this time cadence does allow an assessment of some basic features of storm-time currents and their unique character. Specifically, a differential equatorward shift at dusk, dramatic departures from the conventional distributions, and measurement of the time delay and rate of intensification and equatorward displacement. This analysis takes advantage of new data processing techniques developed under NSF's AMPERE project that allow us to use the full horizontal vector for the Birkeland current inversions. The major advances in Birkeland current determination that will be afforded by AMPERE when high-time resolution Iridium data become available and the status of AMPERE are also discussed.

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