Birkeland currents correlated with direct-current electric fields observed during the CENTAUR Black Brant X rocket experiment

Abstract

Vector magnetic-field observations from two rocket flights in the winter polar cusp during the CENTAUR project show several groups of upward and downward flowing small-scale Birkeland current sheets in the afternoon region of the cusp, whereas none are detected at noon. High correlation with electric-field observations allow calculation of the height-integrated Pedersen conductivity, and an estimate is made of the ionospheric input power density associated with the Birkeland currents. This input power density is comparable to that of a similar summertime experiment at nearly the same magnetic local time and under almost the same interplanetary magnetic-field conditions, despite an order-of-magnitude difference in ionospheric conductivity. Indications are that the magnetospheric energy source for these two events more closely resembles a constant-power generator rather than a constant-voltage or a constant-current generator.