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Temporal-spatial structure of magnetic merging at the magnetopause inferred from 557.7-nm all-sky images

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journal contribution
posted on 2017-03-13, 16:45 authored by N. C. Maynard, J. Moen, W. J. Burke, M. Lester, D. M. Ober, J. D. Scudder, K. D. Siebert, D. R. Weimer, C. T. Russe, A. Balogh
We demonstrate that high-resolution 557.7-nm all-sky images are useful tools for investigating the spatial and temporal evolution of merging on the dayside magnetopause. Analysis of ground and satellite measurements leads us to conclude that high-latitude merging events can occur at multiple sites simultaneously and vary asynchronously on time scales of 30s to 3min. Variations of 557.7nm emissions were observed at a 10s cadence at Ny-Ålesund on 19 December 2001, while significant changes in the IMF clock angle were reaching the magnetopause. The optical patterns are consistent with a scenario in which merging occurs around the rim of the high-latitude cusp at positions dictated by the IMF clock angle. Electrons energized at merging sites represent plausible sources for 557.7nm emissions in the cusp. Polar observations at the magnetopause have directly linked enhanced fluxes of ≥0.5keV electrons with merging. Spectra of electrons responsible for some of the emissions, measured during a DMSP F15 overflight, exhibit "inverted-V" features, indicating further acceleration above the ionosphere. SuperDARN spectral width boundaries, characteristic of open-closed field line transitions, are located at the equatorward edge of the 557.7nm emissions. Optical data suggest that with IMF BY>0, the Northern Hemisphere cusp divides into three source regions. When the IMF clock angle was ~150° structured 557.7-nm emissions came from east of the 13:00 MLT meridian. At larger clock angles the emissions appeared between 12:00 and 13:00 MLT. No significant 557.7-nm emissions were detected in the prenoon MLT sector. MHD simulations corroborate our scenario, showing that with the observed large dipole-tilt and IMF clock angles, merging sites develop near the front and eastern portions of the high-altitude cusp rim in the Northern Hemisphere and near the western part of the cusp rim in the Southern Hemisphere.


The work at MRC was supported by contracts NASW-01011 and NASW-02017, NASA grant NAG5-3182 (subcontract to the University of California, Berkeley) and by the NASA Sun-Earth Connections Theory Program Grant NAG5-8135 (subcontract to Boston University). The ISM was developed under sponsorship of the Defense Threat Reduction Agency, 45 045 Aviation Drive, Dulles, VA 20 166-7517. We also acknowledge support from the Norwegian Research Council, NASA grants and contracts NAG5-2231, NAG5-3328, NAG5-7721, NAG5-7712, NAG5- 7883 NAG5-8119, NAS5-30302, NAS5-30316 and NASW-99014, NAG5-10883, NAG5-121189, and NAG5-11803, and from AFOSR tasks 2311PL13 and 2311AS. The operations of the Hankasalmi and Pykkvibaer radars are funded by PPARC



Annales Geophysicae, 2004, 22 (8), pp. 2917-2942 (26)

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


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Annales Geophysicae


European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)





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