Examining Local Time Variations in the Gains and Losses of Open Magnetic Flux During Substorms

Mooney, M. K., Forsyth, C., Rae, Jonathan, Chisham, G., Coxon, J. C., Marsh, M. S., Jackson, D. R., Bingham, S. and Hubert, B. (2020) Examining Local Time Variations in the Gains and Losses of Open Magnetic Flux During Substorms. Journal of Geophysical Research: Space Physics, 125 (4). e2019JA027369. ISSN 2169-9380

JGR Space Physics - 2020 - Mooney - Examining Local Time Variations in the Gains and Losses of Open Magnetic Flux During.pdf - Published Version
Available under License Creative Commons Attribution 4.0.

Download (19MB) | Preview
Official URL: https://doi.org/10.1029/2019JA027369


The open magnetic flux content of the magnetosphere varies during substorms as a result of dayside and nightside reconnection. The open flux can be calculated from the area of the polar cap, delineated by the open-closed field line boundary (OCB). This study presents a superposed epoch analysis of the location of the OCB and the change in the magnetic flux content in individual nightside MLT sectors during substorm growth, expansion, and recovery phases. Far ultraviolet (FUV) observations from the IMAGE satellite are used to derive a proxy of the OCB location. In the hour prior to substorm onset, the total nightside flux content increases by up to 0.12 GWb on average, resulting in an equatorward expansion of the OCB. Following substorm onset, the OCB contracts toward the pole as the open magnetic flux content decreases by up to 0.14 GWb on average, but the rate of decrease of the total nightside open flux content differs by 5–66% between the three IMAGE far ultraviolet instruments. The OCB does not contract poleward uniformly in all nightside magnetic local time (MLT) sectors after substorm onset. Close to the substorm onset MLT sector, the OCB contracts immediately following substorm onset; however, the OCB in more dawnward and duskward MLT sectors continues to expand equatorward for up to 120 minutes after substorm onset. Despite the continued increase in flux in these sectors after substorm onset, the total nightside flux content decreases immediately at substorm onset, indicating that the nightside reconnection rate exceeds the dayside rate following substorm onset.

Item Type: Article
Additional Information: Funding Information: M. K. M.'s studentship is funded by the U.K. Natural Environment Research Council. C. F. is funded by a NERC Independent Research Fellowship NE/N014480/2. J. C. C. was supported on STFC Consolidated Grant ST/R000719/1.
Uncontrolled Keywords: auroral oval, IMAGE FUV, open-closed field line boundary, substorms, superposed epoch analysis, total flux content
Subjects: F300 Physics
F900 Others in Physical Sciences
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Rachel Branson
Date Deposited: 25 Jan 2022 14:17
Last Modified: 25 Jan 2022 14:30
URI: http://nrl.northumbria.ac.uk/id/eprint/48249

Actions (login required)

View Item View Item


Downloads per month over past year

View more statistics