EISCAT Tromsø
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EISCAT Tromsø
Progress in Interplanetary ScintillationProgress in Interplanetary Scintillation
Bill Coles, University of California at San Diego
A. The Solar Wind:
B. Radio Scattering:
C. Observations:
D. Recent progress:
Eclipse in White Light - HAO - Feb. 16, 1980 - India
Helmet streamers
Typical of Solar Maximum
Eclipse in White Light - HAO - March, 18 1988Typical of Solar Minimum
Coronal Hole
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 andYohkoh SXT
Polar coronal holes
The LASCO C2 Coronagraph at Solar Minimum
Sun
Occulting Disc
Sun Grazing Comet
Closeup of Loops from Trace
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Sun
Solar Wind
driftingintensitypattern
incidentplanewave
compactradio
source
receivingantennas
baseline
Plan view of an ecliptic observation
driftingphase
pattern
angularspectrumof plane waves
Radio Scattering Velocity Measurement
Raw Time Series at 2 Antennas Auto and Cross Correlations
Velocity Map typical of Solar Minimum
1990
1991
1992
1993
1994
1995
1996
1997
Velocity vs Latitudeover Solar Cycle
UCSD Nagoya
Dennison & Hewish, 1966
Hewish & Symonds, 1967
Solar Maximum
VLA Observations of Angular Scattering
s) = e-0.5 D(s)
Anisotropy vs Solar Distance
Model AR(R) of plasma
expected AR(R) for radio wave
The vertical bars indicate variation not statistical error
Helios (equatorial)Ulysses(polar)
VLBA (polar)
Grall et al., VLA par (polar)
Harmon and Coles (mean)
Paetzold & Bird (polar)
VLA perp
Woo & Armstrong(mean)
Scale Dependence of Anisotropy
Manoharan obs
Coles and Harmon tabulation from various sources
Observed coherence scale
Equatorial - no inner scale
Polar - with inner scale
These characteristics of the solar wind microstructure have been known for 20 years. They lead John Harmon to propose that the micro-structure 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 structure2. The elongation would decrease with distance3. The spectrum would be flatter than Kolmogorov4. 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.
240 km
160 km
80 km
The Resolving Power of Long Baselines
951021 at 11 Rs
VPAR alone
VPERP alone
VPERP = 80 km/s
VPAR = (520 - 1200 km/s)
Cross Correlationof 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 Correlationof Intensity in Fast Wind
3 RS at VLBA
Measured IPS Parallel Velocity Distribution
theoretical model
upper envelope = VMODEL + VA
Aug 2 3 4Position of 0854+201 on
GMRT Imaging at 600 MHz.
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.