TY - JOUR
T1 - Longitudinal Development of Poleward Boundary Intensifications (PBIs) of Auroral Emission
AU - Ohtani, S.
AU - Motoba, T.
AU - Gjerloev, J. W.
AU - Ruohoniemi, J. M.
AU - Donovan, E. F.
AU - Yoshikawa, A.
N1 - Funding Information:
We are grateful to Rune Floberghagen, Roger Haagmans, Igino Coco, and the entire SWARM team for the use of SWARM magnetometer data, which can be accessed at https://earth.esa.int/web/guest/swarm/data-access. We are also grateful to S. Mende for the use of the ASI data at Rankin Inlet and Snap Lake and to I. Mann for the magnetometer data at Rankin Inlet. Those ground-based data can be accessed at the THEMIS Mission website (http://themis.ssl.berkeley.edu). Work at APL was supported by NASA grants NNX13AF78G and NNX16AG74G and by NSF grants 1502700 and 1603028.
Funding Information:
We are grateful to Rune Floberghagen, Roger Haagmans, Igino Coco, and the entire SWARM team for the use of SWARM magnetometer data, which can be accessed at https://earth.esa.int/ web/guest/swarm/data-access. We are also grateful to S. Mende for the use of the ASI data at Rankin Inlet and Snap Lake and to I. Mann for the magnetometer data at Rankin Inlet. Those ground-based data can be accessed at the THEMIS Mission website (http://themis.ssl.berkeley.edu). Work at APL was supported by NASA grants NNX13AF78G and NNX16AG74G and by NSF grants 1502700 and 1603028.
PY - 2018/11
Y1 - 2018/11
N2 - We have investigated the longitudinal propagation and extension of the poleward boundary intensifications (PBIs) of auroral emission by examining four events, Events 1–4, which show different spatiotemporal structures. In Event 1 an auroral form extended both eastward and westward immediately following the arrival of a fast polar cap flow and became dynamic as the polar cap flow enhancement continued. The PBI extended 3 hr in local time in a few minutes, which questions the conventional idea that the PBIs are an ionospheric manifestation of distant reconnection. In Events 2 and 3, an auroral form was already dynamic and was collocated with an upward field-aligned current (FAC), which, along with an adjacent downward FAC, formed a longitudinal flow channel confined near the poleward boundary of the auroral oval. Auroral structures propagated in the direction of this longitudinal convection flow. In Event 4, as a transient westward convection flow arrived, a new auroral form developed and extended also westward but noticeably faster than the convection flow, and it faded as it extended. These results suggest that the longitudinal ionospheric convection plays a critical role in the formation and development of the PBIs. They are consistent with a recently proposed idea that the PBIs are an effect of the ionospheric electrostatic polarization, which deflects the enhanced polar cap flow from equatorward to along the auroral oval at its poleward boundary. The contrast between Events 1 and 4 suggests that morphological differences of the PBIs reflect different durations and intensities of the polar cap flow enhancement.
AB - We have investigated the longitudinal propagation and extension of the poleward boundary intensifications (PBIs) of auroral emission by examining four events, Events 1–4, which show different spatiotemporal structures. In Event 1 an auroral form extended both eastward and westward immediately following the arrival of a fast polar cap flow and became dynamic as the polar cap flow enhancement continued. The PBI extended 3 hr in local time in a few minutes, which questions the conventional idea that the PBIs are an ionospheric manifestation of distant reconnection. In Events 2 and 3, an auroral form was already dynamic and was collocated with an upward field-aligned current (FAC), which, along with an adjacent downward FAC, formed a longitudinal flow channel confined near the poleward boundary of the auroral oval. Auroral structures propagated in the direction of this longitudinal convection flow. In Event 4, as a transient westward convection flow arrived, a new auroral form developed and extended also westward but noticeably faster than the convection flow, and it faded as it extended. These results suggest that the longitudinal ionospheric convection plays a critical role in the formation and development of the PBIs. They are consistent with a recently proposed idea that the PBIs are an effect of the ionospheric electrostatic polarization, which deflects the enhanced polar cap flow from equatorward to along the auroral oval at its poleward boundary. The contrast between Events 1 and 4 suggests that morphological differences of the PBIs reflect different durations and intensities of the polar cap flow enhancement.
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U2 - 10.1029/2017JA024375
DO - 10.1029/2017JA024375
M3 - Article
AN - SCOPUS:85056178502
VL - 123
SP - 9005
EP - 9021
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
SN - 2169-9380
IS - 11
ER -