MHD simulations of substorms: Energy flow through the magnetotail.

摘要

Substorms have been a continued matter of discussion over several decades. Magnetometers and other instruments on ground and on satellites have made it possible to quantify the changes that Earth's magnetic field goes through over the course of such an event. Realistic simulations add large scale results to micro scale observations. This dissertation will therefore use both measurements and simulations to analyze six substorms.; The substorms will be analyzed in detail using ground based magnetometer stations and satellite data. The simulations were made using the Lyon-Fedder-Mobarry magneto-hydrodynamic code. By comparing measurements to simulated data I will show that this code simulates basic features of substorms. This dissertation will analyze six substorms, which is three times of what has been done before.; Every simulated event clearly portraits the three phases of a substorm. One can see 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 plasma sheet compression during this time. Generally, the total lobe energy and polar cap flux simultaneously increase during the growth phase and only start decreasing at substorm onset, as measured by the CL index.; 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 being on average one third of the energy that is released from the lobes. It appears that the lobe energy is equipartitioned, with part going earthward, part tailward, part into the endothermic process of plasma sheet dipolarization, and part into the creation of a plasmoid.; The decrease of the magnetic field in the lobes will be shown as well as that its decrease does not coincide with substorm onset. It will be shown from the data that the start of the onset after southward turning of the solar wind magnetic field depends on the strength of the Z component of the IMF, and that the length of the expansion phase is directly linearly dependent on the duration of the southward IMF after onset.