Plasma sheet electromagnetic power generation and its dissipation along auroral field lines

Abstract

During a fortuitous meridional conjunction of Polar and Geotail at the nightside magnetosphere throughout the course of a geomagnetic substorm, measurements of Poynting flux indicate that most of the electromagnetic energy flux density that is radiated in the form of waves at the location of Geotail at ∼18 RE is dissipated before it reaches Polar at ∼5 R E, i.e., above the auroral acceleration region. While the Poynting flux measured at Polar (and to a greater extent at Geotail) is more than sufficient to account for particle acceleration below the satellite, it still represents a small portion of the earthward directed particle energy flux density measured at Geotail. If even a small portion of the bursty bulk flow energy couples to Alfven waves, it would be energetically sufficient to account for the expected auroral energy deposition during substorms. Power dissipation via kinetic Alfven waves along auroral field lines represents a viable mechanism by which localized reconnection flows can slow down. This may explain why fast earthward flows reported at midtail (>30 RE) distances can exist with no near-Earth counterpart and why any putative candidates of an ionospherically reflected flow burst pulse in the tail have very small amplitudes. Copyright 2002 by the American Geophysical Union.