Publication Date:
2017-06-14
Description:
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 IMAGE FUV (Imager for Magnetopause to Aurora Global Exploration Far Ultraviolet) SI12 (spectrographic imager) and WIC (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 MLT. After this the aurorae expand poleward and the brightening stretches dusk- and dawnward, with the duskward expansion being faster. Approximately 20 minutes 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 minutes post onset, the aurorae stay bright for an extended period of time (at least 4 hours 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 minutes after onset. Sawteeth 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 hours to dim, during sawtooth events this process takes less than one hour, despite enhanced reconnection rates. A similar effect is seen in the electron aurorae, albeit not as extreme.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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