HR: 0800h
AN: SM51B-1307    [Abstracts]
TI: What Does the Polar Cap (PC) Index of Geomagnetic Activity Measure?
AU: * Tan, A
EM: arjun.tan@email.aamu.edu
AF: Alabama A&M University, 4900 Meridian St, Normal, AL 35762 United States
AU: Lyatsky, W
EM: lyatsky@cspar.uah.edu
AF: Alabama A&M University, 4900 Meridian St, Normal, AL 35762 United States
AB: The ionospheric convection, driven directly by solar wind electric field, shows energy input from the solar wind to the magnetosphere and ionosphere. One of methods for measurements of this convection is based on magnetic field measurements in the polar cap. For this purpose, the polar cap (PC) geomagnetic activity index has been introduced. This index is derived from magnetic field horizontal components at two near-pole stations in the northern and southern hemispheres. The method is based on the fact that for the homogeneously-conductive ionosphere, magnetic effects from field-aligned and Pedersen currents under the ionosphere compensate one other so that the magnetic variations on the ground show the Hall currents that coincide with the convection flow taken with the opposite sign. It was supposed that magnetic field measurements near the geomagnetic poles are able to describe the directly-driven ionospheric convection during summer months, then this idea had been generalized for all months. However, the magnetic field in the polar cap shows not only local ionospheric currents but also remote field-aligned currents of substorm current wedge, which are responsible for the so-called DP-1 equivalent currents that include "return" equivalent ionospheric currents in the polar cap. The magnetic effect from these currents may significantly contribute to PC index. To investigate contributions from ionospheric convection and substorms to PC index, we used 15-min values of this index, auroral electrojet AL index, and the solar wind and interplanetary magnetic field data for the period of 1995. For reliability, we used several methods. We studied the correlation PC index and both solar wind coupling function and the auroral electrojet AL index showing substorm activity. We found that the correlation between PC and AL indices is significantly better than that between PC index and the coupling function. Additionally, for low values of the coupling function when the correlation between PC index and the solar wind may be neglected, there is a good correlation between PC and AL indices. These results demonstrate obviously a strong contribution from substorms to PC index. This finding is consistent with the recent results by Huang [2005] who also concluded that the solar wind electric field and substorms give comparable contributions to PC index.
DE: 2441 Ionospheric storms (7949)
DE: 2788 Magnetic storms and substorms (7954)
DE: 7894 Instruments and techniques
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005