Abstract
Abstract. We examine the distribution and propagation of energy in the plasma sheet and lobes using observations and simulations for three substorms. The substorms occurred on 9 March 1995, 10 December 1996, and 27 August 2001 and have been simulated using the Lyon-Fedder-Mobarry magneto-hydrodynamic code. All three events occur over North America and show a clear substorm current wedge over the ground magnetometer chains of Alaska, Canada, and Greenland. The three simulations show the thinning of the plasma sheet during the growth phase of the event and an increase in the relative amount of thermal energy due to the compression of the plasma sheet. Generally, the total lobe energy, polar cap flux, and lobe magnetic field strength simultaneously increase during the growth phase, and polar cap flux and total lobe energy only start dropping at substorm onset, as measured by the CANOPUS magnetometer chain. Starting at time of onset and continuing throughout the expansion phase a transfer of magnetic energy from the lobes into the plasma sheet occurs, with the increase in the plasma sheet energy ranging from 30–40% of the energy that is released from the lobes.
Highlights
Substorms are the process by which energy that was loaded into the magnetotail from the solar wind is explosively released in the magnetosphere-ionosphere system
The total lobe energy, polar cap flux, and lobe magnetic field strength simultaneously increase during the growth phase, and polar cap flux and total lobe energy only start dropping at substorm onset, as measured by the CANOPUS magnetometer chain
Starting at time of onset and continuing throughout the expansion phase a transfer of magnetic energy from the lobes into the plasma sheet occurs, with the increase in the plasma sheet energy ranging from 30–40% of the energy that is released from the lobes
Summary
Substorms are the process by which energy that was loaded into the magnetotail from the solar wind is explosively released in the magnetosphere-ionosphere system. The reconnection region causes a disruption of the growth phase enhanced cross-tail currents. S. Brogl et al.: Magnetotail dynamics and energy evolution during substorms down the tail when reconnection proceeds to open field lines, and this is generally thought to be coincident with the expansion phase onset (Baker et al, 1985, 1996). It was thought that the energy loading and unloading processes were different during the growth and expansion phase of the substorm (Baker et al, 1985), but it was clarified that both are due to reconnection processes of open and closed field lines in the dayside and nightside of Earth, respectively (Baker et al, 1996). We present first a brief introduction of the code and procedures used to do this analysis, followed by a discussion of the energy dynamics of the three events showing that the results are consistent, followed by our conclusion
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