Statistical dependence of auroral ionospheric currents on solar wind and geomagnetic parameters from 5 years of CHAMP satellite data

摘要

The effects of the solar wind dynamic pressure (P), the z component ofthe solar wind magnetic field (B_z), the merging electric field (E_m),season and the K_p index on R1 and R2 field-aligned currents are studiedstatistically using magnetic field data from the CHAMP satellite during2001–2005. The ionospheric and field-aligned currents are determined fromthe magnetic field data by the recently developed 1-D Spherical ElementaryCurrent System (SECS) method. During southward IMF, increasing |B_z| isobserved to clearly increase the total field-aligned current, while duringnorthward IMF, the amount of field-aligned current remains fairly constantregardless of |B_z|. The dependence of the field-aligned current on B_zis given by |I_r[MA]|=0.054·B_z[nT]2−0.34·B_z[nT]+2.4. With increasing P, the intensity of thefield-aligned current is also found to increase according to|I_r[MA]|=0.62·P[nPa]+1.6, and the auroral oval isobserved to move equatorward. Increasing E_m produces similar behaviour,described by |I_r[MA]|=1.41·E_m[mV/m]+1.4. While theabsolute intensity of the ionospheric current is stronger during negativethan during positive B_z, the relative change in the intensity of thecurrents produced by a more intense solar wind dynamic pressure is observedto be approximately the same regardless of the B_z direction. IncreasingK_p from 0 to ≥5 widens the auroral oval and moves it equatorward frombetween 66°–74° AACGM latitude to59°–71° latitude. The total field aligned currentas a function of K_p is given by |I_r[MA]|=1.1·K_p+0.6.In agreement with previous studies, total field-aligned current in the summeris found to be 1.4 times stronger than in the winter.