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S.R. Spangler, P.S. Kortenkamp, R.L. Mutel (Univ. Iowa)
We have made Very Long Baseline Interferometer (VLBI) observations of radio sources close to the Sun. For the sources discussed here, the lines of sight passed from 17 R\odot to 26 R\odot from the Sun. We have measured the temporal fluctuations in the interferometer phase due to solar wind turbulence. We have fit the measured phase power spectra with theoretical models, and extracted values for the speed at which the irregularities move with respect to the antennas. These speeds range from 190 to 340 kilometers per second, and are consistent with bulk solar wind speeds deduced from LASCO coronagraph observations. The derived speeds are lower than the sum of the bulk solar wind flow speed and the Alfvén speed, as would be expected if the irregularities are associated with outwardly-propagating Alfvén waves. The significance of this result for models of solar wind turbulence will be discussed. This research was supported by the NSF through grant ATM99-86887.