Generator and load regions in the magnetotail

Abstract:

Energy conversion processes play an important role for the dynamics of the Earth's magnetotail. They can be probed through the power density, E·J, where E and J are the electric field and the current density, respectively. In a load process, for example magnetic reconnection and auroral acceleration, electromagnetic energy is converted into kinetic energy and E·J>0. In a generator (dynamo) process, such as the deceleration of fast magnetotail flows, energy is transferred in the opposite direction and E·J<0. Multispacecraft missions such as Cluster and MMS are favorable for observational investigations of energy conversion using E·J, since at least four simultaneous magnetic field measurements are needed for estimating the full vector J. By using Cluster E·J data from 2001-2004 we have investigated the statistical properties of plasma sheet energy conversion regions, and the role of the plasma sheet in channeling solar wind power to the ionosphere. Studying a fortunate interval of conjugated Cluster-FAST data, we have been able to associate the auroral acceleration observed at lower FAST altitudes with possible auroral generator regions at higher Cluster altitudes. In addition, in our investigations, we have used E·J to study both plasma acceleration and deceleration processes. In particular, we have found that E·J can be used as a tool for identifying possible magnetic reconnection events from large sets of data, e.g., from the Cluster and MMS missions.