AAS 207th Meeting, 8-12 January 2006
Session 111 Solar Activity
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[111.05] New Constraints on Plasma Turbulence in the Solar Corona

S.R. Spangler, L.G. Spitler (University of Iowa)

One suggestion for coronal heating invokes the dissipation of high frequency, Alfvén-ion cyclotron waves which are generated in the photosphere and chromosphere and propagate into the corona. As we have previously noted (Spangler and Mancuso 2000, ApJ 530, 491) the properties of such waves can be constrained by radioastronomical observations. The observational effect is Faraday screen depolarization, in which stochastic Faraday rotation randomizes the polarization position angle on scales smaller than the telescope beam. We present observations made with the NRAO Very Large Array on August 16 and 18, 2003, when the radio galaxy 3C228 was viewed through the corona at heliocentric distances of 6.7 and 5.2 R\odot, respectively. The depolarization parameter D \equiv m/m_0 was measured, where m is the fractional linear polarization measured through the corona, and m0 is the intrinsic degree of polarization. Measurements were available for both hot spots of 3C228, and on both days of observation. The measurements are consistent with D=1 for both components on both days. These results are in agreement with, but superior to, previous reports of no coronal screen depolarization. Equations from Spangler and Mancuso (2000) are used to constrain the dimensionless amplitude and outer scale of the coronal turbulence. Turbulence with a dimensionless amplitude of 50 % or greater, and outer scale larger than 1000-2000 km, would have produced depolarization close to, or in excess of our limits. Turbulence with smaller dimensionless amplitude and outer scale would not have been detected with these measurements. This research was supported by grant ATM-0354782 from the National Science Foundation.

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