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

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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.