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Mean Energy Flux, Associated Derived Height‐Integrated Conductances, and Field‐Aligned Current Magnitudes Evolve Differently During a Substorm

Carter, JA; Milan, SE; Forsyth, C; Lester, ME; Walach, M‐T; Gjerloev, J; Paxton, LJ; (2023) Mean Energy Flux, Associated Derived Height‐Integrated Conductances, and Field‐Aligned Current Magnitudes Evolve Differently During a Substorm. Journal of Geophysical Research: Space Physics , 128 (2) , Article e2022JA030942. 10.1029/2022ja030942. Green open access

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Abstract

We examine the average evolution of precipitation-induced height-integrated conductances, along with field-aligned currents (FACs), in the nightside sector of the polar cap over the course of a substorm. Conductances are estimated from the average energy flux and mean energies derived from auroral emission data. Data are binned using a superposed epoch analysis on a normalized time grid based on the time between onset and recovery phase (δt) of each contributing substorm. We also examine conductances using a fixed time binning of width 0.25 hr. We split the data set by magnetic latitude of onset. We find that the highest conductances are observed for substorms with onsets that occur between 63 and 65° magnetic latitude, peaking at around 11 mho (Hall) and 4.8 mho (Pedersen). Substorms with onsets at higher magnetic latitudes show lower conductances and less variability. Changes in conductance over the course of a substorm appear primarily driven by changes (about 40% at onset) in the average energy flux, rather than the average energy of the precipitation. Average energies increase after onset slower than energy flux, later these energies decrease slowly for the lowest latitude onsets. No clear expansion of the main region 1 and region 2 FACs is observed. However, we do see an ordering of the current magnitudes with magnetic latitude of onset, particularly for region 1 downwards FAC in the morning sector. Peak current magnitudes occur slightly after or before the start of the recovery phase for the normalized and fixed-time grids.

Type: Article
Title: Mean Energy Flux, Associated Derived Height‐Integrated Conductances, and Field‐Aligned Current Magnitudes Evolve Differently During a Substorm
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2022ja030942
Publisher version: https://doi.org/10.1029/2022ja030942
Language: English
Additional information: Copyright © 2023. The Authors. This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Keywords: ionosphere, magnetosphere-ionosphere coupling, conductance, aurora, field-aligned currents, substorms
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10165359
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