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Statistical analysis of MMS observations of energetic electron escape observed at/beyond the dayside magnetopause
Author(s) -
Cohen Ian J.,
Mauk Barry H.,
Anderson Brian J.,
Westlake Joseph H.,
Sibeck David G.,
Turner Drew L.,
Fennell Joseph F.,
Blake J. Bern,
Jaynes Allison N.,
Leonard Trevor W.,
Baker Daniel N.,
Spence Harlan E.,
Reeves Geoff D.,
Giles Barbara J.,
Strangeway Robert J.,
Torbert Roy B.,
Burch James L.
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2017ja024401
Subject(s) - magnetosheath , magnetopause , physics , magnetosphere , geophysics , pitch angle , electron , magnetic reconnection , context (archaeology) , solar wind , space physics , computational physics , earth's magnetic field , astrophysics , magnetic field , geology , paleontology , quantum mechanics
Observations from the Energetic Particle Detector (EPD) instrument suite aboard the Magnetospheric Multiscale (MMS) spacecraft show that energetic (greater than tens of keV) magnetospheric particle escape into the magnetosheath occurs commonly across the dayside. This includes the surprisingly frequent observation of magnetospheric electrons in the duskside magnetosheath, an unexpected result given assumptions regarding magnetic drift shadowing. The 238 events identified in the 40 keV electron energy channel during the first MMS dayside season that exhibit strongly anisotropic pitch angle distributions indicating monohemispheric field‐aligned streaming away from the magnetopause. A review of the extremely rich literature of energetic electron observations beyond the magnetopause is provided to place these new observations into historical context. Despite the extensive history of such research, these new observations provide a more comprehensive data set that includes unprecedented magnetic local time (MLT) coverage of the dayside equatorial magnetopause/magnetosheath. These data clearly highlight the common escape of energetic electrons along magnetic field lines concluded to have been reconnected across the magnetopause. While these streaming escape events agree with prior studies which show strong correlation with geomagnetic activity (suggesting a magnetotail source) and occur most frequently during periods of southward IMF, the high number of duskside events is unexpected and previously unobserved. Although the lowest electron energy channel was the focus of this study, the events reported here exhibit pitch angle anisotropies indicative of streaming up to 200 keV, which could represent the magnetopause loss of >1 MeV electrons from the outer radiation belt.