Energy as a tracer of magnetospheric processes: GUMICS-4 global MHD results and observations compared

This paper reviews quantitative analysis results of the energy transfer and dissipation processes in the GUMICS-4 global MHD simulation. Reconnection power dissipating magnetic energy, dynamo power transferring energy from plasma to the field, and energy flux transport across the magnetopause surface are all examined separately and shown to yield consistent results. This is used to argue that magnetic reconnection is the process controlling the energy transfer, even though it is not localized near the reconnection line. The most important factors controlling the reconnection efficiency are the interplanetary magnetic field (IMF) orientation and the solar wind speed, while the IMF magnitude and solar wind density play a lesser role. During northward IMF, the reconnection efficiency is larger for high speed and low IMF than for low speed and high IMF magnitude, even though the solar wind electric field in both cases is the same. Moreover, increasing pressure by increasing density has a different effect from equal increase of pressure by increasing the solar wind speed. Comparison with statistical observational results shows that the simulation results are in qualitative agreement with the observations, which significantly increases our confidence in interpreting the simulation results.