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Monitoring the dayside and nightside reconnection rates during various auroral events using IMAGEFUV and SuperDARN data

By B. Hubert, M. Palmroth, Steve E. Milan, Adrian Grocott, P. Janhunen, K. Kauristie, S.W.H. Cowley, T.I. Pulkkinen and J.-C. Gérard


This paper was presented at the Eighth International Conference on Substorms (ICS-8), held at the University of Calgary, Alberta, Canada, 27-31 March, 2006, and published in Proceedings of the Eighth International Conference on Substorms, edited by M. Syrjäsuo and E.F. Donovan, pp. 117-121. It is available from only entryThe Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft was launched in 2000 with\ud several imaging instruments onboard. The Far UltraViolet (FUV) experiment was devoted to the imaging of the N2 LBH\ud (Wideband Imaging Camera - WIC-), OI 135.6 nm (Spectrographic Imager -SI13-) and Doppler-shifted Lyman-alpha\ud auroral emission (SI12). The Doppler-shifted Lyman-alpha emission is solely due to proton precipitation and is not\ud contaminated by dayglow, allowing to monitor the auroral oval at dayside as well as at nightside. Remote sensing of\ud the polar aurora can be advantageously completed by ground based data of the Super Dual Auroral Radar Network\ud (SuperDARN) that monitors the ionospheric convection flow pattern in the polar region. In the present study, the SI12\ud images are used to determine the open/closed (o/c) field line boundary, and monitor its movement. The SuperDARN data\ud are used to compute the electric field of the polar cap at the location of the o/c boundary. The total electric field is then\ud computed along the boundary accounting for its movement applying Faraday’s law, so that the dayside and nightside\ud reconnection voltages can be retrieved. This procedure is applied to monitor the dayside and nightside reconnection\ud voltages during several events. The phases of the substorm cycle can be identified: the growth phase characterised by\ud intense dayside flux opening and occasionally pseudobreakups, the onset which is immediately followed by a maximum\ud intensity of the flux closure rate, and the recovery phase during which the flux closure voltage slowly returns to\ud undisturbed values, with occasional poleward boundary intensifications which appear along with a slight intensification of\ud the closure voltage. The transient response to an interplanetary shock is also monitored and reveals a sharp intensification\ud of the closure rate, despite a low open flux value for the studied case. A case of auroral streamer event has also been\ud studied, presenting a remarkably large flux closure rate. This feature is related with a bursty enhancement of the\ud ionospheric convection. Bursty bulk flow events can thus be associated as well with enhanced flux closure. The tool that\ud we developed can also be used to study the relations between the topology of the magnetotail and the flux closure rate\ud as well as to set up proxies relating the solar wind conditions with the dayside reconnection voltage. The monitoring of\ud dayside and nightside reconnection rates can thus be considered as an investigation tool for nearly all types of auroral\ud features

Publisher: University of Calgary.
Year: 2006
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