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IMF dependence of saturn's auroras: Modelling study of HST and Cassini data from 12-15 February 2008

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journal contribution
posted on 24.10.2012, 09:06 by E. S. Belenkaya, I. I. Alexeev, M. S. Blokhina, V. V. Kalegaev, E. J. Bunce, S. W. H. Cowley, J. D. Nichols, G. Provan, V. G. Petrov
To gain better understanding of auroral processes in Saturn's magnetosphere, we compare ultraviolet (UV) auroral images obtained by the Hubble Space Telescope (HST) with the position of the open-closed field line boundary in the ionosphere calculated using a magnetic field model that employs Cassini measurements of the interplanetary magnetic field (IMF) as input. Following earlier related studies of pre-orbit insertion data from January 2004 when Cassini was located ~ 1300 Saturn radii away from the planet, here we investigate the interval 12–15 February 2008, when UV images of Saturn's southern dayside aurora were obtained by the HST while the Cassini spacecraft measured the IMF in the solar wind just upstream of the dayside bow shock. This configuration thus provides an opportunity, unique to date, to determine the IMF impinging on Saturn's magnetosphere during imaging observations, without the need to take account of extended and uncertain interplanetary propagation delays. The paraboloid model of Saturn's magnetosphere is then employed to calculate the magnetospheric magnetic field structure and ionospheric open-closed field line boundary for averaged IMF vectors that correspond, with appropriate response delays, to four HST images. We show that the IMF-dependent open field region calculated from the model agrees reasonably well with the area lying poleward of the UV emissions, thus supporting the view that the poleward boundary of Saturn's auroral oval in the dayside ionosphere lies adjacent to the open-closed field line boundary.

Funding

Work at the Institute of Nuclear Physics, Moscow State University was supported by Royal Society (London)/RFBR Grant No 09-02-92603-KO a, and by RFBR Grants 07-05-00529 and 09-05-00798. Work at Leicester was also supported by the Royal Society/RFBR Grant (JP080836), and by STFC grants PP/E000983/1 and ST/H002480/1.

History

Citation

Annales Geophysicae, 2010, 28 (8), pp. 1559-1570

Published in

Annales Geophysicae

Publisher

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

issn

0992-7689

eissn

1432-0576

Copyright date

2010

Available date

24/10/2012

Publisher version

http://www.ann-geophys.net/28/1559/2010/angeo-28-1559-2010.html

Language

en

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