IMF <i>B_y</i> dependence of region 1 Birkeland currents near noon

Abstract

We have conducted a statistical study of large‐scale Birkeland currents, hot plasma, and the B y component of the interplanetary magnetic field. Forty‐eight Viking orbits from July 19, 1986, to September 2, 1986, were used in the study during a time period when the 3‐ R E geocentric apogee was located near the dayside high‐latitude region usually associated with the polar cusp. We first compared the location of magnetosheathlike electrons to the region 1 and “traditional cusp” Birkeland current systems near noon. It was found that the region 1 Birkeland current system was colocated with the region of most intense magnetosheathlike electron flux. We therefore infer that the “traditional cusp” current system, located poleward of the region 1 system, is associated with field lines that extend to the plasma mantle in the outer magnetosphere. Using this same data base a statistical study between the B y component of the IMF and the flow direction of the region 1 Birkeland current system as a function of magnetic local time was performed. We determined that the flow direction of the region 1 current system near noon depends on the B y component of IMF. The meridian that separates the dawnside and duskside region 1 Birkeland currents shifted to magnetic local times before noon when B y was less than 0 nT, and to the afternoon when B y was greater than 0 nT. The extent of the shift away from noon was dependent on the magnitude of the IMF B y component.