TY - JOUR
T1 - Radar Observations of Flows Leading to Longitudinal Expansion of Substorm Onset Over Alaska
AU - Lyons, Larry R.
AU - Liu, Jiang
AU - Nishimura, Yukitoshi
AU - Wang, Chih Ping
AU - Reimer, Ashton S.
AU - Bristow, William A.
AU - Hampton, Don L.
AU - Shi, Xueling
AU - Varney, Roger H.
AU - Donovan, Eric F.
N1 - Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.
PY - 2021/2
Y1 - 2021/2
N2 - Longitudinal expansion of brightening of the substorm onset arc likely represents longitudinal expansion of the substorm onset instability. We used Poker Flat radar campaign auroral observations to identify seven substorm onsets seen east or west of the radar that expanded into the radar field-of-view. The radar observations were used to show flows relative to the expanding onset aurora. Flow enhancements were found equatorward (poleward) of the westward (eastward) longitudinal expansion of the onset arc brightening that agree with plasma sheet bubble modeling. This lends significant additional supporting evidence that an incoming reduced entropy flow channel leads to onset. As a flow channel enters the auroral oval (plasma sheet) from the polar cap (magnetotail lobes) and starts to move equatorward (earthward in the plasma sheet) as a bubble, it simultaneously expands azimuthally due to the combination of electric drift along dawnward tilted equipotentials and westward magnetic drift of more energetic ions. As the azimuthally expanding bubble reaches near the equatorward boundary of the electron auroral oval, it leads to the onset instability indicated by the auroral beading and associated flows if conditions are appropriate. The instability grows in the initial onset region, as it simultaneously extends longitudinally with the continued azimuthal expansion of the bubble within the plasma sheet. Additionally, after onset, the auroral bulge expands poleward and can lead to a westward traveling surge. We observe strong flows heading toward the front of the surge that appear to bring low entropy plasma, perhaps from the polar cap, into the surge.
AB - Longitudinal expansion of brightening of the substorm onset arc likely represents longitudinal expansion of the substorm onset instability. We used Poker Flat radar campaign auroral observations to identify seven substorm onsets seen east or west of the radar that expanded into the radar field-of-view. The radar observations were used to show flows relative to the expanding onset aurora. Flow enhancements were found equatorward (poleward) of the westward (eastward) longitudinal expansion of the onset arc brightening that agree with plasma sheet bubble modeling. This lends significant additional supporting evidence that an incoming reduced entropy flow channel leads to onset. As a flow channel enters the auroral oval (plasma sheet) from the polar cap (magnetotail lobes) and starts to move equatorward (earthward in the plasma sheet) as a bubble, it simultaneously expands azimuthally due to the combination of electric drift along dawnward tilted equipotentials and westward magnetic drift of more energetic ions. As the azimuthally expanding bubble reaches near the equatorward boundary of the electron auroral oval, it leads to the onset instability indicated by the auroral beading and associated flows if conditions are appropriate. The instability grows in the initial onset region, as it simultaneously extends longitudinally with the continued azimuthal expansion of the bubble within the plasma sheet. Additionally, after onset, the auroral bulge expands poleward and can lead to a westward traveling surge. We observe strong flows heading toward the front of the surge that appear to bring low entropy plasma, perhaps from the polar cap, into the surge.
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U2 - 10.1029/2020JA028148
DO - 10.1029/2020JA028148
M3 - Article
AN - SCOPUS:85102144621
VL - 126
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
SN - 2169-9380
IS - 2
M1 - e2020JA028148
ER -