Dynamics of Global-Scale Birkeland Currents During Geomagnetic Storm
Tuesday, September 29, 2015
Haje Korth, Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, Brian J Anderson, Johns Hopkins University, Baltimore, MD, United States, Colin L Waters, University of Newcastle, Callaghan, Australia and Robin J Barnes, JHU/APL, Laurel, MD, United States
Abstract:
The Active Magnetosphere and Polar Electrodynamics Response Experiment (AMPERE) provides the first ever continuous global measurements of the Birkeland currents linking the ionosphere and high-altitude magnetosphere with sufficiently fine temporal cadence to monitor the currents through geomagnetically active conditions. The present analysis focusses primarily on three storm periods: 5-6 August 2011, 17-18 March 2015, and 13-15 May 2015. The first two storms were driven by coronal mass ejections whereas the third was driven by a high-speed stream. At storm commencement the shock arrival corresponds to a strong enhancement of Birkeland currents at high latitudes on the dayside, which corresponds to intense reconnection flows and leads to intense heating in the dayside high-latitude thermosphere. The storm main-phase corresponds to rapid equatorward expansion of the currents as well as multiple onsets and expansions of the currents on the nightside, reflecting sporadic and explosive onsets or intensifications of return convection in the magnetotail. Such sub-storm like intensifications continue throughout the main phase. In addition, a new set of upward and downward currents is found in the nighttime evening sector during the storm main phase. These currents are equatorward of the Region 1/Region 2 system associated with statistical descriptions, and are present over a limited local time region. We suggest that this new system is generated entirely by plasma pressure intensifications resulting from convection into the inner magnetosphere and is associated with the main phase partial ring current. We also contrast the dynamics between storms driven by CMEs and high-speed streams to identify the effects of enhanced IMF and flow speed, respectively, on the solar wind–magnetosphere interaction.
