Effect of Bγ IMF in substorm current wedge formation

Based on the data of longitudinal chain of midlatitude stations in the northern hemisphere, substorm-associated field-alighned currents (FACs) are examined. A comparison of IMF component variations with surface FAC characteristics in substorm sites is performed. It is shown that the ratio between the upward and downward surface FAC intensities depends on By IMF. In this regard, the conditions are discussed that favor currents flowing from the dayside cusp to nightside auroral region. These currents, which position is dependent on By IMF direction, can be responsible for difference between the upward and downward current-wedge-associated FACs.