Reconnection Inside a Dipolarization Front of a Diverging Earthward Fast Flow
Escoubet, C. P.; Fazakerley, A. N.; Le Contel, O.; Nakamura, R.; Volwerk, M.; Carr, C.; Torbert, R. B.; Vörös, Z.; Burch, J. L.; Giles, B. L.; Nakamura, T. K. M.; Settino, A.; Panov, E. V.; Roberts, O. W.; Schmid, D.; Korovinskiy, D.; Hosner, M.; Blasl, K. A.; Marshall, A. T.; Denton, R. E.; Dandouras, I. S.
Austria, Japan, Hungary, United States, France, Netherlands, United Kingdom
Abstract
We examine a Dipolarization Front (DF) event with an embedded electron diffusion region (EDR), observed by the Magnetospheric Multiscale (MMS) spacecraft on 08 September 2018 at 14:51:30 UT in the Earth's magnetotail by applying multi-scale multipoint analysis methods. In order to study the large-scale context of this DF, we use conjunction observations of the Cluster spacecraft together with MMS. A polynomial magnetic field reconstruction technique is applied to MMS data to characterize the embedded electron current sheet including its velocity and the X-line exhaust opening angle. Our results show that the MMS and Cluster spacecraft were located in two counter-rotating vortex flows, and such flows may distort a flux tube in a way that the local magnetic shear angle is increased and localized magnetic reconnection may be triggered. Using multi-point data from MMS we further show that the local normalized reconnection rate is in the range of R ∼ 0.16 to 0.18. We find a highly asymmetric electron in- and outflow structure, consistent with previous simulations on strong guide-field reconnection events. This study shows that magnetic reconnection may not only take place at large-scale stable magnetopause or magnetotail current sheets but also in transient localized current sheets, produced as a consequence of the interaction between the fast Earthward flows and the Earth's dipole field.