Search for formation of global current system during substorm through observation of ionospheric response at mid-latitudinal region

Abstract:

For comprehensive understanding of global current system from polar to equatorial ionosphere during substorm, we investigate a local time (LT) dependence of magnetic and electric fields in the mid-latitude ionosphere.

It is well known that the development of Region 1 type field-aligned current (R1 FAC) at the polar ionosphere is linked with development of magnetospheric convection system, while development of Region 2 type field-aligned current (R2 FAC) at sub-auroral region is linked with development of diamagnetic current [Iijima and Potemra, 1976, 1978].

The substorm current-wedge is excited by dipolarization process of geomagnetic fields with plasma injection to the inner magnetosphere, which shows the R1 FAC closure to the westward auroral electrojet current inside auroral oval. Simultaneously the R2 FAC is activated by increasing of plasma pressure accompanied by the plasma injection to the inner magnetosphere during dipolarization process. Both of current systems excite ionospheric current connecting from polar to equatorial ionosphere, but their polarities are opposite and response time and duration to the substorm are different. Hence the R2-type FAC not only shields growth of ionospheric part of current wedge system reaching from high to equatorial region, but also causes overshielding effect that sometimes excites the low latitudinal ionospheric current in the opposite direction to that of current wedge system [Kelley et al., 1979; Gonzales et al., 1979]

In this study, to identify cause of geomagnetic filed variations during substorm at mid-latitudinal region, we investigate ionospheric variations at the substorm onset and its LT dependence. We used electric field data from the HF Doppler radar at Palatunka, Russia, and magnetic field data from SuperMag and MAGDAS. The preliminary results show that when the station is inside the current-wedge of the substorm and the magnetic field observe the upward current growing with the substorm onset, the electric field at mid-latitudes is eastward for about ten minutes. This electric field is thought to be an induced electric field that prevents the magnetosonic waves excited in the substorm onset from reaching and growing in the mid-latitude magnetosphere. We report the results of the LT dependence, which were verified in detail on a global scale.