TY - JOUR
T1 - The Source of Auroral Omegas
AU - Nykyri, Heidi K.
AU - Weygand, J.M.
AU - El-Alaoui, Mostafa
AU - Nykyri, Katariina
N1 - Weygand, J. M., El-Alaoui, M., & Nykyri, H. K. (2022). The source of auroral omegas. Journal of Geophysical Research: Space Physics, 127, e2021JA029908. https://doi. org/10.1029/2021JA029908
PY - 2022/1/8
Y1 - 2022/1/8
N2 - The auroral wave-like structures called “omega bands” appear within the post-midnight sector auroral oval with shapes resembling the Greek letter omega, and are typically associated with the recovery phase of substorms. Prior work and MHD simulations suggest both high speed earthward flows and postmidnight flow shears are possible omega band source mechanisms. However, what produces omega bands is not well understood. It is most likely that the paucity of concurrent magnetospheric data has limited our ability to understand fully the mechanism responsible for the generation of the omega bands. We have identified about 263 auroral omegas in seven different THEMIS all sky cameras (ASCs) over a 10 year period. A fraction appear to form from north-south streamers, but some appear to form from east-west auroral arcs. Fifty-one of the 263 Ω also have conjugate or near conjugate THEMIS and GOES spacecraft data. There is evidence in about 80% of these events that high speed earthward flows have occurred prior to or at about the same time as the auroral omega observation. This evidence consists of high speed earthward flows, magnetic field dipolarizations, particle injections into the inner magnetosphere, and auroral streamers. 11 events also show plasma flow data azimuthally along the inner magnetosphere, but for six of these events the Vy component is inconsistent with the auroral omega direction of motion. Of the remaining five events, four have Vy flow shear events but also show evidence of magnetic field dipolarizations, particle injections into the inner magnetosphere, and auroral streamers. Our observations suggest high speed earthward flows are more likely to be the source of auroral omega bands.
AB - The auroral wave-like structures called “omega bands” appear within the post-midnight sector auroral oval with shapes resembling the Greek letter omega, and are typically associated with the recovery phase of substorms. Prior work and MHD simulations suggest both high speed earthward flows and postmidnight flow shears are possible omega band source mechanisms. However, what produces omega bands is not well understood. It is most likely that the paucity of concurrent magnetospheric data has limited our ability to understand fully the mechanism responsible for the generation of the omega bands. We have identified about 263 auroral omegas in seven different THEMIS all sky cameras (ASCs) over a 10 year period. A fraction appear to form from north-south streamers, but some appear to form from east-west auroral arcs. Fifty-one of the 263 Ω also have conjugate or near conjugate THEMIS and GOES spacecraft data. There is evidence in about 80% of these events that high speed earthward flows have occurred prior to or at about the same time as the auroral omega observation. This evidence consists of high speed earthward flows, magnetic field dipolarizations, particle injections into the inner magnetosphere, and auroral streamers. 11 events also show plasma flow data azimuthally along the inner magnetosphere, but for six of these events the Vy component is inconsistent with the auroral omega direction of motion. Of the remaining five events, four have Vy flow shear events but also show evidence of magnetic field dipolarizations, particle injections into the inner magnetosphere, and auroral streamers. Our observations suggest high speed earthward flows are more likely to be the source of auroral omega bands.
KW - auroral omega
KW - high speed earthward flows
KW - dipolarizations
KW - Kelvin-Helmholtz instability
KW - particle injections
KW - hemispherically conjugate observations
UR - https://commons.erau.edu/publication/1945
U2 - 10.1029/2021JA029908
DO - 10.1029/2021JA029908
M3 - Article
SN - 2169-9402
VL - 127
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
ER -