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Energetic, ∼5–90 keV neutral atom imaging of a weak substorm with STEREO/STE
Author(s) -
Wang Linghua,
Lin R. P.,
Parks G. K.,
Brandt P. C.,
Roelof E. C.,
Sample J. G.,
Eastwood J. P.,
Larson D. E.,
Curtis D. W.,
Luhmann J. G.
Publication year - 2010
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2010gl042964
Subject(s) - substorm , physics , ring current , asymmetry , geosynchronous orbit , energetic neutral atom , van allen probes , proton , flux (metallurgy) , equator , pitch angle , spectral line , local time , astrophysics , magnetosphere , atomic physics , electron , satellite , van allen radiation belt , geophysics , latitude , astronomy , plasma , nuclear physics , materials science , quantum mechanics , metallurgy , statistics , mathematics
We present imaging and high resolution energy spectra of energetic ∼5–90 keV neutral atoms (ENA) of a weak geomagnetic substorm (Dst > −8 nT and AE ≲ 200 nT), made by the Suprathermal Electron (STE) instrument on the STEREO B spacecraft. Enhanced ENA emissions were observed coming from around local midnight near the equator with different spatial distribution and/or temporal behavior at ∼5–20keV compared to ∼20–90 keV. By forward modeling using a parameterized ring‐current model, we show that the ENA images imply the parent equatorial protons have pitch‐angle distributions peaked at 90°, an energy spectrum consistent with in situ proton measurements at geosynchronous orbit, and a spatial asymmetry with the maximum flux at midnight for 5–20 keV and at 2240 MLT for 20–90 keV. These are the first ENA measurements at ∼5 to 26 keV from low altitude, and the first for such weak activity.