Anomalous Reconnection Layer at Earth's Dayside Magnetopause
Sonnerup, B. U. Ö.
Phan, T.
Fuselier, S. A.
Haaland, S.
Denton, R. E.
Burch, J. L.
Trattner, K. J.
Giles, B. L.
Gershman, D. J.
Cohen, I. J.
Russell, C. T.
DOI: https://doi.org/10.1029/2021JA029678
Persistent URL: http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/9901
Phan, T.; 3 Space Sciences Laboratory University of California Berkeley CA USA
Fuselier, S. A.; 4 Southwest Research Institute San Antonio TX USA
Haaland, S.; 6 Birkeland Centre for Space Science University of Bergen Bergen Norway
Denton, R. E.; 9 Department of Physics and Astronomy Dartmouth College Hanover NH USA
Burch, J. L.; 4 Southwest Research Institute San Antonio TX USA
Trattner, K. J.; 10 LASP University of Colorado Boulder CO USA
Giles, B. L.; 11 NASA Goddard Space Flight Center Greenbelt MD USA
Gershman, D. J.; 11 NASA Goddard Space Flight Center Greenbelt MD USA
Cohen, I. J.; 13 The Johns Hopkins University Applied Physics Laboratory Laurel MD USA
Russell, C. T.; 14 Department of Earth Planetary and Space Sciences University of California Los Angeles CA USA
Abstract
Observations by the Magnetospheric Multiscale spacecraft (MMS) of an unusual layer, located between the dayside magnetosheath and the magnetosphere, alternating with encounters with the magnetosheath during an extended time period between December 31, 2015 and January 01, 2016, when the interplanetary magnetic field was strongly southward and the Earth's dipole tilt large and negative, are presented. It appears to have been magnetically connected to both magnetosphere and magnetosheath. The layer appears to be located mostly on closed field lines and was bounded by a rotational discontinuity (RD) at its magnetosheath edge and by the magnetosphere on its earthward side. A separatrix layer, with heated magnetosheath electrons streaming unidirectionally along the field lines, was present sunward of the RD. We infer that the layer was started by a dominant reconnection site well north of the spacecraft and that it may have gained additional width, from a large drop in solar wind density and ram pressure, which preceded the beginning of the event by more than an hour. Relative to the magnetosheath, in which the magnetic field was strongly southward, this unusual layer was characterized by a less southward, more dawnward magnetic field of lower magnitude. The plasma density and flow speed in the region were lower than in the magnetosheath, albeit with Alfvénic jetting occurring at the magnetosheath edge as well as at the magnetospheric edge of the layer. The closing of the magnetic field lines requires the existence of another reconnection site, located southward/tailward of MMS.
Key Points:
Magnetopause encounter for strongly southward interplanetary magnetic field, low solar wind Alfvén Mach number, and large dipole tilt.
Persistent and broad magnetopause layer with magnetospheric O+ and heated magnetosheath plasma.
Inferred dominant reconnection site near northern cusp, far from the Magnetospheric Multiscale spacecraft location.