Statistical Birkeland current distributions from magnetic field observations by the Iridium constellation

By Brian J. Anderson, H. Korth, Colin L. Waters, D. L. Green, P. Stauning. 2008

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We present a statistical analysis of Birkeland currents derived from Iridium magnetometer data acquired in the Northern Hemisphere to determine the dependence of large-scale currents on the interplanetary magnetic field (IMF) direction. Because the Iridium data span nearly seven years, we can restrict analysis to only those intervals with sta- ble currents. We used image comparison to quantify the con- sistency between successive one-hour current distributions and selected 1550 two-hour intervals, 5% of the data, for analysis. Results include: no statistically significant aver- age currents are present poleward of 80 during southward IMF; Region-2 currents are weak and confined to latitudes >65 during northward IMF; there is marked contrast be- tween currents for northward and southward IMF but the evo- lution of the patterns is continuous with IMF rotation. The directions of flows inferred from the most poleward currents are more consistent with theoretical expectations of transport away from magnetopause reconnection than previous results. We attribute the differences to the restriction in this analysis to intervals having relatively stable distributions of current so that the data set corresponds more nearly to pure states of the system. the dynamic state of the system. The M-I system and hence the distribution and intensity of the large-scale Birkeland cur- rents is largely governed by the magnitude and direction of the interplanetary magnetic field (IMF), the solar wind speed and density, and the ionospheric conductivity. Characteriz- ing these dependencies is central to understanding driven M- I electrodynamics. Previous studies have determined global distributions of the large-scale Birkeland currents and their relationship to solar wind and IMF parameters by statistical analysis of single-satellite observations ( Iijima and Potemra, 1978; Weimer, 2001, 2005; Papitashvili et al., 2002). These studies significantly advanced our understanding of M-I cou- pling and may represent the most comprehensive analyses possible with these data. From this body of work we know that the IMF orientation is the dominant factor controlling the distribution of the currents and that while the IMF magnitude and the solar wind speed and density affect the intensity of the currents, they do not to first order alter the pattern of the

Subfields: Astronomy and Astrophysics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/986330010d9c24b894a16aa3d04389c11b037998

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Particle Acceleration in the Magnetotail and Aurora (2012, background): “The “upward/downward” FA current topology is found at large scales, typical for the auroral oval (Anderson et al. 2008; Iijima and Potemra 1976; Kamide 1982; Ohtani et al. 2010; Weimer 2001) as illustrated in Fig.”
The Magnetic Field of Mercury (2010, methodology): “The first flyby also revealed a boundary layer within and adjacent to the outbound magnetopause crossing, but there were no indications of reconnection on the outbound magnetopause crossing (Anderson et al. 2008b; Slavin et al. 2008).”
Development of large‐scale Birkeland currents determined from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (2014, methodology): “This basic pattern has been derived statistically from several data sets [Papitashvili et al., 2002; Weimer, 2005; Anderson et al., 2008; He et al., 2012].”