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EISCAT Tromsø Progress in Interplanetary Scintillation Bill Coles, University of California at San Diego A. The Solar Wind: B. Radio Scattering: C. Observations: D. Recent progress: Helmet streamers Eclipse in White Light - HAO - Feb. 16, 1980 - India Typical of Solar Maximum Coronal Hole Eclipse in White Light - HAO - March, 18 1988 Typical of Solar Minimum The Solar Wind 1. The existence of the solar wind could have been inferred from the shape of helmet streamers. 2. It could also have been inferred from measurements of the aurora. 3. It was inferred from observations of the direction of the ionic comet-tails. Coronal hole Soft X-ray Telescope (SXT) on Yohkoh Satellite Mauna Loa Mk3 WLC and Yohkoh SXT Polar coronal holes The LASCO C2 Coronagraph at Solar Minimum Occulting Disc Sun Sun Grazing Comet Closeup of Loops from Trace QuickTime™ and a YUV420 codec decompressor are needed to see this picture. Plan view of an ecliptic observation drifting intensity receiving pattern antennas drifting phase pattern Solar Wind baseline angular spectrum of plane waves Sun incident plane wave compact radio source Radio Scattering Velocity Measurement Raw Time Series at 2 Antennas Auto and Cross Correlations Velocity Map typical of Solar Minimum 1990 1994 1991 1995 1992 1996 1993 1997 Velocity vs Latitude over Solar Cycle UCSD Dennison & Hewish, 1966 Hewish & Symonds, 1967 Solar Maximum Nagoya VLA Observations of Angular Scattering r(s) = e-0.5 D(s) Anisotropy vs Solar Distance The vertical bars indicate variation not statistical error Model AR(R) of plasma expected AR(R) for radio wave Scale Dependence of Anisotropy Ulysses (polar) Helios (equatorial) Paetzold & Bird (polar) VLBA (polar) Woo & Armstrong (mean) Harmon and Coles (mean) Grall et al., VLA par (polar) VLA perp Manoharan obs Coles and Harmon tabulation from various sources Equatorial - no inner scale Polar - with inner scale Observed coherence scale These characteristics of the solar wind microstructure have been known for 20 years. They lead John Harmon to propose that the microstructure was caused by obliquely propagating Alfven waves because these waves would satisfy all four of the properties discussed: 1. They would cause radial elongation of the structure 2. The elongation would decrease with distance 3. The spectrum would be flatter than Kolmogorov 4. The waves would damp at the ion inertial scale. The problem is that these waves would also cause the intensity diffraction pattern to move outwards with respect to the flow at the group velocity of the waves VA. For quite some time we did not think this was compatible with the observations. We now believe that the velocity observations are compatible with these waves. The Resolving Power of Long Baselines 80 km 160 km 240 km VPAR = (520 - 1200 km/s) VPERP = 80 km/s VPERP alone VPAR alone 951021 at 11 Rs Cross Correlation of Intensity in Fast Wind 10 RS at VLBA -solar minimum -half the baselines shown -slow and fast peaks clear -best fit model not unique Cross Correlation of Intensity in Fast Wind 3 RS at VLBA Measured IPS Parallel Velocity Distribution upper envelope = VMODEL + VA theoretical model GMRT Imaging at 600 MHz. Position of 0854+201 on Aug 2 3 4 Implication Variations in angular scattering are not obviously correlated with variations in density. Angular scattering is a column integral of density2, whereas white light brightness is a column integral of density. Apparently scattering near the Sun is dominated by small but dense structures which are invisible in white light because their contribution to integrated density is negligible, however they contribute to scattering because they contribute significantly to the integral of density2.