Abstract
Abstract. The effects of the solar wind dynamic pressure (P), the z component of the solar wind magnetic field (Bz), the merging electric field (Em), season and the Kp index on R1 and R2 field-aligned currents are studied statistically using magnetic field data from the CHAMP satellite during 2001–2005. The ionospheric and field-aligned currents are determined from the magnetic field data by the recently developed 1-D Spherical Elementary Current System (SECS) method. During southward IMF, increasing |Bz| is observed to clearly increase the total field-aligned current, while during northward IMF, the amount of field-aligned current remains fairly constant regardless of |Bz|. The dependence of the field-aligned current on Bz is given by |Ir[MA]|=0.054·Bz[nT]2−0.34·Bz[nT]+2.4. With increasing P, the intensity of the field-aligned current is also found to increase according to |Ir[MA]|=0.62·P[nPa]+1.6, and the auroral oval is observed to move equatorward. Increasing Em produces similar behaviour, described by |Ir[MA]|=1.41·Em[mV/m]+1.4. While the absolute intensity of the ionospheric current is stronger during negative than during positive Bz, the relative change in the intensity of the currents produced by a more intense solar wind dynamic pressure is observed to be approximately the same regardless of the Bz direction. Increasing Kp from 0 to ≥5 widens the auroral oval and moves it equatorward from between 66°–74° AACGM latitude to 59°–71° latitude. The total field aligned current as a function of Kp is given by |Ir[MA]|=1.1·Kp+0.6. In agreement with previous studies, total field-aligned current in the summer is found to be 1.4 times stronger than in the winter.
Highlights
A significant part of the solar wind energy that penetrates the Earth’s magnetosphere is dissipated in the polar ionospheres
Using particle precipitation data from the Defense Meteorological Satellite Program (DMSP) spacecraft, Boudouridis et al (2003) studied the effect of large solar wind dynamic pressure increases on the location, size and intensity of the auroral oval during three events with various interplanetary magnetic field (IMF) orientation
The determination of the ionospheric current density from the magnetic field measured by the satellite (Br, Bθ, Bφ) using the 1-D Spherical Elementary Current System (SECS) method is illustrated in the bottom panel of Fig. 1: The horizontal ionospheric current density at the altitude of 100 km can be divided into curl-free and divergence-free parts
Summary
A significant part of the solar wind energy that penetrates the Earth’s magnetosphere is dissipated in the polar ionospheres. Seasonal variations in local solar radiation affect the ionospheric conductivity and thereby the intensity of the currents. Due to the effect of the dipole tilt on the magnetospheric configuration, the dayside fieldaligned currents move poleward in the summer hemisphere and equatorward in the winter hemisphere, while the nightside field-aligned currents have the opposite seasonal dependence (Ohtani et al, 2005). On the other hand, using a global MHD simulation, they found that Joule heating was positively correlated with the solar wind dynamic pressure both during southward and northward IMF. Using particle precipitation data from the Defense Meteorological Satellite Program (DMSP) spacecraft, Boudouridis et al (2003) studied the effect of large solar wind dynamic pressure increases on the location, size and intensity of the auroral oval during three events with various IMF orientation.
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