Radio wave scattering observations of the solar corona: First-order measurements of expansion velocity and turbulence spectrum using Viking and Mariner 10 spacecraft
Solar conjunction of Mars on 1976 November 25 occurred very near the beginning of solar cycle 21, about 4 months after the first Viking spacecraft arrived at the planet. Radio wave scattering data were collected at 3.6 and 13 cm wavelengths, using the radio link between the Viking orbiters and the Earth. These data allow measurements of solar wind properties over a range of heliocentric radial distance from approx.6 to 44 R/sub sun/ with solar latitudes ranging from -17/sup 0/ to +7/sup 0/. Observations with Mariner 10 during a period of moderate solar activity in 1974 cover from 6 to 24 R/sub sun/ and from approx.20/sup 0/ to near 90/sup 0/. We have found that the temporal frequency variance spectrum of amplitude fluctuations is useful for characterizing the bulk motion of the plasma. This spectrum has an approximately constant low frequency plateau and a power-law high frequency asymptote; the plateau-asymptote intersection frequency provides a measure of the solar wind velocity V. We also obtain the spectral index p of electron density turbulence, Phi/sub N/approx.kappa/sup -p/, where kappa is spatial wavenumber. These results apply to a cylindrical region oriented with its axis along the radio ray path and its center at the point of closest approach to the Sun. The measurements of V and p cover some 78/sup d/ for Viking and 49/sup 2/ for Mariner 10 and show the combined effects of changing heliocentric distance rho, solar latitude theta, and solar longitude Psi, as well as solar activity. The Viking results can be regarded as a function primary of rho and Psi since the observations are concentrated in the equatorial regions when solar activity was near minimum. For Mariner 10, rho, theta, and Psi variations were important. The Viking results show an abrupt change in V(rho) and the turbulence spectral index at approx.15 R/sub sun/.
- Research Organization:
- Stanford Center for Radar Astronomy
- OSTI ID:
- 5756632
- Journal Information:
- Astrophys. J.; (United States), Vol. 249:1
- Country of Publication:
- United States
- Language:
- English
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GENERAL PHYSICS
SOLAR CORONA
EXPANSION
RADAR
DATA ANALYSIS
DATA PROCESSING
MARINER SPACE PROBES
RADIOWAVE RADIATION
SOLAR ELECTRONS
SOLAR WIND
TURBULENCE
VIKING SPACE PROBES
WAVE PROPAGATION
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
LEPTONS
MEASURING INSTRUMENTS
PROCESSING
RADIATIONS
RANGE FINDERS
SOLAR ACTIVITY
SOLAR PARTICLES
SOLAR RADIATION
SPACE VEHICLES
STELLAR RADIATION
VEHICLES
640104* - Astrophysics & Cosmology- Solar Phenomena