Near-sun solar wind turbulence investigations using very long baseline interferometry

Details Near-sun solar wind turbulence investigations using very long baseline interferometry Near-sun solar wind turbulence investigations using very long baseline interferometry

Nov 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........6k&link_type=abstract

Ph.D dissertation, 2005. 95 pages; United States -- Iowa: The University of Iowa; 2005. Publication Number: AAT 3184727. DAI-B

Computer Science

Solar Wind, Turbulence, Interferometry, Scintillations

Scientific paper

In the absence of in situ spacecraft measurements inside 0.3 AU, remote sensing observations of the solar wind throughout its acceleration region (5-50 [Special characters omitted.] ) provide information on characteristics of plasma turbulence, which may assess the role such turbulence plays in heating the corona and accelerating the solar wind. I have used the Very Long Baseline Array interferometer to make two observing sessions of radio sources (1999 and 2002) over solar elongations from 6 to 36 solar radii and at frequencies of 2.3, 5.0, and 8.4 GHz. I measured solar-wind-induced temporal fluctuations in the interferometer phase which contain information on the level and propagation speed of solar wind density fluctuations. Radio images and visibility amplitude data were analyzed to determine the magnitude and anisotropy of the angular broadening due to the solar wind turbulence. A solar wind model was employed to glean further information from our observational data. Analysis of visibility phase fluctuations returned a wide range of turbulence levels and propagation speeds for different regions of the solar wind and during different observing times. The level of turbulence ([Special characters omitted.] ) determined from both projects showed spatial and temporal variability in this parameter while propagation speeds were from 200 km/s to 650 km/s. An important new result is that angular broadening of the 1999 sources appears anisotropic in a direction approximately perpendicular to the interplanetary magnetic field. This result indicates that the turbulence is comprised of field-aligned density irregularities on the 200-5000 km scales as well as the 1-100 km scales probed by earlier measurements and is compatible with modern theories of the nature of magnetohydrodynamic turbulence. The use of MHD models of the solar wind to interpret radio propagation measurements is a relatively new technique. Their use here, in conjunction with these and prior observations, have produced estimates for the plasma parameter m . Observations from 1998 and 1999 combined to yield a value for this quantity of 5.7 x 10 -3 which is in good agreement with previous determinations. Observations from 2002 returned a reduced value of 2.8 x 10 -4 which implies reduced level of solar wind density fluctuations.

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