Statistical Dependence of the Large-Scale Birkeland Currents on Solar Wind Parameters

Details Statistical Dependence of the Large-Scale Birkeland Currents on Solar Wind Parameters Statistical Dependence of the Large-Scale Birkeland Currents on Solar Wind Parameters

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsa33a1613k&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SA33A-1613

Physics

2400 Ionosphere (6929), 2407 Auroral Ionosphere (2704), 2409 Current Systems (2721), 2431 Ionosphere/Magnetosphere Interactions (2736), 2447 Modeling And Forecasting

Scientific paper

Since February 1999, distributions of the large-scale field-aligned Birkeland currents have been derived continuously from magnetic perturbations measured globally by the Iridium constellation of satellites. In a statistical study, over 1500 two-hour intervals (5% of the data) were identified for which the currents were stable to within at least 45% overlap between successive hours, corresponding to conditions in the solar wind were sufficiently stable to obtain reliable Birkeland currents. Organized by the interplanetary magnetic field (IMF) clock angle, the statistical current distributions show familiar Regrion-1 and Region-2 currents for southward IMF, NBZ currents for northward IMF, and a continuous distortion of the currents with IMF clock angle consistent with changes in the location of outflow from magnetopause reconnection (Anderson et al. 2008). Here we extend the statistical analysis to examine the dependence of the large-scale Birkeland currents on solar wind electric field in the plane normal to the Earth-Sun line, Eyz, to assess the sensitivity to the strength of the solar wind dynamo, Alfvén Mach number to assess the influence of dayside reconnection mass loading, and dynamic pressure to investigate the dependence on ram pressure. The current intensities are first corrected for variations in EUV-produced ionospheric conductance, normalizing the current densities to zero dipole tilt conditions. Findings include: (1) with increasing solar wind electric field the large-scale Birkeland currents shift duskward and expand equatorward, and the total current intensifies; (2) the total current intensifies with increasing solar wind dynamic pressure by 0.4 MA/nPa; (3) the total current intensifies with increasing Alfvén Mach number by 0.07 MA per unit Alfvén Mach number change. The analysis and implications are discussed.

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