Abstract
Abstract. The goal of this study is to find a way to statistically estimate the Hall to Pedersen conductance ratio α from ground magnetic data. We use vector magnetic data from the CHAMP satellite to derive this relation. α is attained from magnetic satellite data using the 1-D Spherical Elementary Current Systems (SECS). The ionospheric equivalent current density can either be computed from ground or satellite magnetic data. Under the required 1-D assumption, these two approaches are shown to be equal, which leads to the advantage that the statistics are not restricted to areas covered by ground data. Unlike other methods, using magnetic satellite measurements to determine α ensures reliable data over long time sequences. The statistical study, comprising over 6000 passes between 55° and 76.5° northern geomagnetic latitude during 2001 and 2002, is carried out employing data from the CHAMP satellite. The data are binned according to activity and season. In agreement with earlier studies, values between 1 and 3 are typically found for α. Good compatibility is found, when α attained from CHAMP data is compared with EISCAT radar measurements. The results make it possible to estimate α from the east-west equivalent current density Jφ; [A/km]: α=2.07/(36.54/|Jφ|+1) for Jφ<0 (westward) and α=1.73/(14.79/|Jφ+1) for Jφ0 (eastward). Using the same data, statistics of ionospheric and field-aligned current densities as a function of geomagnetic latitude and MLT are included. These are binned with respect to activity, season and IMF BZ and BY. For the first time, all three current density components are simultaneously studied this way on a comparable spatial scale. With increasing activity, the enhancement and the equatorward expansion of the electrojets and the R1 and R2 currents is observed, and in the nightside, possible indications of a Cowling channel appear. During southward IMF BZ, the electrojets and the R1 and R2 currents are stronger and clearer than during northward BZ. IMF BY affects the orientation of the pattern.
Highlights
Ionospheric conductances and current distributions, in addition to being important to ionospheric studies, reflect the dynamics of the entire magnetosphere through its coupling to the ionosphere
Under the required 1-D assumption, the equivalent currents determined from ground and satellite magnetic data were shown to be equal, which increased the amount of data available for the statistics by extending it outside ground-based coverage
The conductance ratio was attained from magnetic satellite data by using the 1-D Spherical Elementary Current Systems (SECS) method
Summary
Ionospheric conductances and current distributions, in addition to being important to ionospheric studies, reflect the dynamics of the entire magnetosphere through its coupling to the ionosphere. Section 4: Magnetic vector data from the CHAMP satellite during 2001–2002 is used to ps of the ionospheric and field-aligned current density cLo.mJpuounseonltas,eatnadl.t:oEessttaimblaisthinagrαelaftrioonmshJipeqbetween Jφ and α. When the error is approximately less than 60%, groundand satellite-based Jφ can be considered to be equivalent This means, in addition to confirming the reliability of the 1-D SECS method, that in our pursuit for an estimate for the conductance ratio as a function of ground-based magnetic data, we no longer need to consider the actual ground data at all, but instead can rely solely on CHAMP data with Jφ representing the ground data. Assuming that the geomagnetic field is radial a unit slope is drawn in blue To create this plot, data from 124 (B=−Ber ), and the convection electric field horizontal satellite passes over IMAGE with an error smaller than 60% during (E=Eθ eθ +Eφeφ), Ohm’s law in the ionosphere. This result was attained by assuming uniform conductances in addition to 1-D:ness, it should be reasonably safe to state that in 1-D cases, Eφ/Eθ ≈0 and α=−Jφ/Jθ
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