Fischer, G. and Gurnett, D. A. and Zarka, P. and Moore, L. and Dyudina, U. A. (2011) Peak electron densities in Saturn’s ionosphere derived from the low‐frequency cutoff of Saturn lightning. Journal of Geophysical Research Space Physics, 116 . Art No. A04315. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20110519-081016971
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Radio bursts from Saturn lightning have been observed by the Cassini Radio and Plasma Wave Science instrument at frequencies of a few megahertz during several month-long storms since 2004. As the radio waves traverse Saturn's ionosphere on their way to the spacecraft, one can determine the peak electron density from the measurement of the low-frequency cutoff below which the radio bursts are not detected. In this way we obtained 231 profiles of peak electron densities that cover all Saturnian local times at a kronocentric latitude of 35°S, where the storms were spotted by the Cassini camera. Peak electron densities show a large variation at dawn and dusk and are around 5 × 10^4 cm^(−3), in fair agreement with radio occultation measurements at midlatitudes. At noon and midnight, the densities are typically somewhat above 10^5 cm^(−3) and around 10^4 cm^(−3), respectively. The diurnal variation is about 1 to 2 orders of magnitude for averaged profiles over one storm at 35°S. This is somewhat less compared to previous Voyager measurements which showed more than 2 orders of magnitude variation. The diurnal variation as well as the peak electron densities of Saturn's ionosphere tend to decrease with the decreasing solar EUV flux from 2004 until the end of 2009.
|Additional Information:||© 2011 American Geophysical Union. Received 6 October 2010; revised 24 January 2011; accepted 26 January 2011; published 21 April 2011. G. F. was supported by a grant (project P21295‐N16) from the Austrian Science Fund (FWF) and by a short‐term research scholarship at the University of Iowa funded by NASA through contract 1356500 from the Jet Propulsion Laboratory. The International Space Science Institute (ISSI) in Bern, Switzerland, is acknowledged for hosting two meetings of the ISSI International Team on Saturn Aeronomy (number 166). The team of the CELIAS/SEM experiment on board the SOHO spacecraft is acknowledged for providing the solar EUV fluxes via its Web page at the Space Sciences Center of the University of Southern California. G. F. thanks his trainee Dino Mehic for his help with data processing. Many amateurs observed Saturn with their optical telescopes and helped in the determination of the storm locations. Among them, G. F. specially thanks T. Barry, M. Delcroix, C. Go, D. Peach, R. Vandebergh, and A. Wesley. Masaki Fujimoto thanks the reviewers for their assistance in evaluating this paper.|
|Subject Keywords:||Saturn, lightning, ionosphere, SED, electron density|
|Official Citation:||Fischer, G., D. A. Gurnett, P. Zarka, L. Moore, and U. A. Dyudina (2011), Peak electron densities in Saturn’s ionosphere derived from the low‐frequency cutoff of Saturn lightning, J. Geophys. Res., 116, A04315, doi:10.1029/2010JA016187|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||19 May 2011 15:51|
|Last Modified:||26 Dec 2012 13:14|
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