Volwerk, M. and Brown, M. E. and Dessler, A. J. and Sandel, B. R. (1997) Evidence for short cooling time in the Io plasma torus. Geophysical Research Letters, 24 (9). pp. 1147-1150. ISSN 0094-8276. http://resolver.caltech.edu/CaltechAUTHORS:20121002-103911803
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We present empirical evidence for a radiative cooling time for the Io plasma torus that is about a factor of ten less than presently accepted values. We show that brightness fluctuations of the torus in the extreme ultraviolet (EUV) at one ansa are uncorrelated with the brightness at the other ansa displaced in time by five hours, either later or earlier. Because the time for a volume of plasma to move from one ansa to the other is only five hours, the cooling time must be less than this transport time in order to wipe out memory of the temperatures between ansae. Most (∼80–85%) of the EUV emission comes from a narrow (presumably ribbon‐like) feature within the torus. The short cooling time we observe is compatible with theoretical estimates if the electron density in the ribbon is ∼10^4/cm^3. The cooling time for the rest of the torus (which radiates the remaining 15–20% of the power) is presumably consistent with the previously derived 20‐hour values. A nearly‐continuous heating in both longitude and time is needed to maintain the EUV visibility of the torus ribbon—a requirement not satisfied by presently available theories.
|Additional Information:||© 1997 American Geophysical Union. Received 21 January 1997; accepted 25 March 1997. We thank Floyd Herbert, Tom Hill, Bill Smyth, and Vytenis Vasyliunas for helpful comments and advice. This research was supported in part by a subcontract to NASA contract NAS7-918. MEB is supported by NASA grant HF-010556.02.94A from the Space Telescope Science Institute.|
|Official Citation:||Volwerk, M., M. E. Brown, A. J. Dessler, and B. R. Sandel (1997), Evidence for short cooling time in the Io plasma torus, Geophys. Res. Lett., 24(9), 1147–1150, doi:10.1029/97GL00966.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||02 Oct 2012 17:52|
|Last Modified:||27 Dec 2012 02:47|
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