Year: 2021
Type: article
Abstract: We report a unique conjugate observation of fast flows and associated current sheet disturbances in the near‐Earth magnetotail by MMS (Magnetospheric Multiscale) and Cluster preceding a positive bay onset of a small substorm at ∼14:10 UT, September 8, 2018. MMS and Cluster were located both at X ∼ −14 RE. A dipolarization front (DF) of a localized fast flow was detected by Cluster and MMS, separated in the dawn‐dusk direction by ∼4 RE, almost simultaneously. Adiabatic electron acceleration signatures revealed from the comparison of the energy spectra confirm that both spacecraft encounter the same DF. We analyzed the change in the current sheet structure based on multi‐scale multi‐point data analysis. The current sheet thickened during the passage of DF, yet, temporally thinned subsequently associated with another flow enhancement centered more on the dawnward side of the initial flow. MMS and Cluster observed intense perpendicular and parallel current in the off‐equatorial region mainly during this interval of the current sheet thinning. Maximum field‐aligned currents both at MMS and Cluster are directed tailward. Detailed analysis of MMS data showed that the intense field‐aligned currents consisted of multiple small‐scale intense current layers accompanied by enhanced Hall‐currents in the dawn‐dusk flow‐shear region. We suggest that the current sheet thinning is related to the flow bouncing process and/or to the expansion/activation of reconnection. Based on these mesoscale and small‐scale multipoint observations, 3D evolution of the flow and current‐sheet disturbances was inferred preceding the development of a substorm current wedge.
DOI: 10.1029/2021ja029518
Institutions: Austrian Academy of Sciences, Space Research Institute, University of Graz, St Petersburg University, Space Science Institute, Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, The Aerospace Corporation, Uppsala University, Swedish Institute of Space Physics, Southwest Research Institute, Imperial College London, Centre National de la Recherche Scientifique, Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, European Space Research and Technology Centre, Goddard Space Flight Center, Observatoire de Paris, Laboratoire de Phonétique et Phonologie, Laboratoire de Physique des Plasmas, University of California, Los Angeles, University of New Hampshire
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3207165326