University of Leicester
Walach_et_al-2017-Journal_of_Geophysical_Research-_Space_Physics.pdf (2 MB)

Comparative study of large-scale auroral signatures of substorms, steady magnetospheric convection events, and sawtooth events

Download (2 MB)
journal contribution
posted on 2017-08-24, 13:01 authored by M-T. Walach, S. E. Milan, K. R. Murphy, J. A. Carter, B. A. Hubert, A. Grocott
This paper investigates the auroral evolution during different magnetospheric modes: substorms, steady magnetospheric convection, and sawtooth events. We undertake a superposed epoch analysis using data from the Imager for Magnetopause-to-Aurora Global Exploration Far Ultraviolet spectrographic imager and wideband imaging camera for each of these event types. We find that the auroral oval narrows and shows an equatorward movement prior to substorm onset. At substorm onset, the auroral oval brightens explosively near 23 magnetic local time (MLT). After this the aurorae expand poleward and the brightening stretches duskward and dawnward, with the duskward expansion being faster. Approximately 20 min after substorm onset, the aurorae begin to dim. Steady magnetospheric convection events with preceding substorms initially show the same signatures as substorms, but instead of the recovery after 20 min postonset, the aurorae stay bright for an extended period of time (at least 4 h after onset). Despite continued dayside driving of the system during steady magnetospheric convection events, we see a reconfiguration in the nightside auroral activity, taking place between 120 to 150 min after onset. Sawtooth events show very similar signatures to substorms, except for the auroral emission being much brighter, covering a wider MLT extent, and taking significantly less time to recover. The proton aurorae during substorms take ∼2–4 h to dim, during sawtooth events this process takes less than 1 h, despite enhanced reconnection rates. A similar effect is seen in the electron aurorae, albeit not as extreme.


We thank the PI of IMAGE, J.L. Burch and the PI of FUV, S.B. Mende for the original IMAGE data set. M.-T.W. was supported by a studentship from the Science and Technology Facilities Council, UK. S.E.M. and J.A.C. were supported on the STFC grant ST/K001000/1 and ST/N000749/1. K.M. is partly funded by a Natural Sciences and Engineering Research Council of Canada Postdoctoral Fellowship. B.H. is supported by the FRS-FNRS. A.G. is supported by the STFC grant STM001059/1 and NERC grant NE/P001556/1. The original IMAGE data are available through the IMAGE FUV homepage (



Journal of Geophysical Research: Space Physics, 2017, 122 (6), pp. 6357-6373 (17)

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


  • VoR (Version of Record)

Published in

Journal of Geophysical Research: Space Physics


American Geophysical Union (AGU), Wiley





Acceptance date


Copyright date


Available date


Publisher version


The code used to generate the plots in this paper are stored in University of Leicester computers and are available on request.