Rights statement: Copyright 2011 by the American Geophysical Union
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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Midnight sector observations of auroral omega bands
AU - Wild, J.A.
AU - Woodfield, E.E.
AU - Donovan, E.
AU - Fear, R.C.
AU - Grocott, A.
AU - Lester, M.
AU - Fazakerley, A.N.
AU - Lucek, E.
AU - Khotyaintsev, Y.
AU - Andre, M.
AU - Kadokura, A.
AU - Hosokawa, K.
AU - Carlson, C.
AU - McFadden, J.P.
AU - Glassmeier, K.H.
AU - Angelopoulos, V.
AU - Björnsson, G.
N1 - Copyright (2011) American Geophysical Union. Further reproduction or electronic distribution is not permitted.
PY - 2011/3/18
Y1 - 2011/3/18
N2 - We present observations of auroral omega bands on 28 September 2009. Although generally associated with the substorm recovery phase and typically observed in the morning sector, the features presented here occurred just after expansion phase onset and were observed in the midnight sector, dawnward of the onset region. An all‐sky imager located in northeastern Iceland revealed that the omega bands were ∼150 × 200 km in size and propagated eastward at ∼0.4 km s−1 while a colocated ground magnetometer recorded the simultaneous occurrence of Ps6 pulsations. Although somewhat smaller and slower moving than the majority of previously reported omega bands, the observed structures are clear examples of this phenomenon, albeit in an atypical location and unusually early in the substorm cycle. The THEMIS C probe provided detailed measurements of the upstream interplanetary environment, while the Cluster satellites were located in the tail plasma sheet conjugate to the ground‐based all‐sky imager. The Cluster satellites observed bursts of 0.1–3 keV electrons moving parallel to the magnetic field toward the Northern Hemisphere auroral ionosphere; these bursts were associated with increased levels of field‐aligned Poynting flux. The in situ measurements are consistent with electron acceleration via shear Alfvén waves in the plasma sheet ∼8 RE tailward of the Earth. Although a one‐to‐one association between auroral and magnetospheric features was not found, our observations suggest that Alfvén waves in the plasma sheet are responsible for field‐aligned currents that cause Ps6 pulsations and auroral brightening in the ionosphere. Our findings agree with the conclusions of earlier studies that auroral omega bands have a source mechanism in the midtail plasma sheet.
AB - We present observations of auroral omega bands on 28 September 2009. Although generally associated with the substorm recovery phase and typically observed in the morning sector, the features presented here occurred just after expansion phase onset and were observed in the midnight sector, dawnward of the onset region. An all‐sky imager located in northeastern Iceland revealed that the omega bands were ∼150 × 200 km in size and propagated eastward at ∼0.4 km s−1 while a colocated ground magnetometer recorded the simultaneous occurrence of Ps6 pulsations. Although somewhat smaller and slower moving than the majority of previously reported omega bands, the observed structures are clear examples of this phenomenon, albeit in an atypical location and unusually early in the substorm cycle. The THEMIS C probe provided detailed measurements of the upstream interplanetary environment, while the Cluster satellites were located in the tail plasma sheet conjugate to the ground‐based all‐sky imager. The Cluster satellites observed bursts of 0.1–3 keV electrons moving parallel to the magnetic field toward the Northern Hemisphere auroral ionosphere; these bursts were associated with increased levels of field‐aligned Poynting flux. The in situ measurements are consistent with electron acceleration via shear Alfvén waves in the plasma sheet ∼8 RE tailward of the Earth. Although a one‐to‐one association between auroral and magnetospheric features was not found, our observations suggest that Alfvén waves in the plasma sheet are responsible for field‐aligned currents that cause Ps6 pulsations and auroral brightening in the ionosphere. Our findings agree with the conclusions of earlier studies that auroral omega bands have a source mechanism in the midtail plasma sheet.
KW - omega bands
KW - substorm
KW - cluster
KW - aurora
U2 - 10.1029/2010JA015874
DO - 10.1029/2010JA015874
M3 - Journal article
VL - 116
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - A00I30
M1 - A00I30
ER -