Separatrix regions of magnetic reconnection at the magnetopause
1Swedish Institute of Space Physics, P.O. Box 537, 751 21 Uppsala, Sweden
2Department of Physics and Astronomy, Space and Plasma Physics, P.O. Box 515, 751 20 Uppsala, Sweden
3Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
4Centre d'Etude Spatiale des Rayonnements, CNRS, Toulouse, France
5Department of Physics and Technology, University of Bergen, Bergen, Norway
6Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany
7Mullard Space Science Laboratory, University College London, Dorking, UK
Abstract. Using data from the four Cluster spacecraft we study the separatrix regions of magnetic reconnection sites at the dayside magnetopause under conditions when reconnection is occurring in the magnetopause current layer which separates magnetosheath plasma from the hot magnetospheric plasma sheet. We define the separatrix region as the region between the separatrix – the first field line opened by reconnection – and the reconnection jet (outflow region). We analyze eight separatrix region crossings on the magnetospheric side of the magnetopause and present detailed data for two of the events. We show that characteristic widths of the separatrix regions are of the order of ten ion inertial lengths at the magnetopause. Narrow separatrix regions with widths comparable to a few ion inertial lengths are rare. We show that inside the separatrix region there is a density cavity which sometimes has complex internal structure with multiple density dips. Strong electric fields exist inside the separatrix regions and the electric potential drop across the regions can be up to several kV. On the magnetosheath side of the region there is a density gradient with strong field aligned currents. The observed strong electric fields and currents inside the separatrix region can be important for a local energization of ions and electrons, particularly of ionospheric origin, as well as for magnetosphere-ionosphere coupling.
Lindstedt, T., Khotyaintsev, Yu. V., Vaivads, A., André, M., Fear, R. C., Lavraud, B., Haaland, S., and Owen, C. J.: Separatrix regions of magnetic reconnection at the magnetopause, Ann. Geophys., 27, 4039-4056, doi:10.5194/angeo-27-4039-2009, 2009.