Solar Wind and Solar Rotation.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar Wind and Solar Rotation. Brandt, John C. Abstract Braking of stellar rotation due to angular momentum loss in a stellar wind is an attractive, intrinsic mechanism compatible with the observed rotations of main sequence stars; accurate determination for the solar case is essential as a calibration point. The azimuthal velocity Wt of the solar wind plasma near the orbit of earth was first assigned a value of 9+3 km/sec from a study of the orientations of Type I comet tails by Brandt (Astrophys. J. 144, 1221,1966). Improvements in the analysis do not change this result. In addition, the results are supported by the fact that higher values of Wt are correlated with the higher values of the geomagnetic index Kp, as might be expected. Independent confirmation comes from studies with the Vela satellites by Strong, Asbridge, Bame, and Hundhausen (Conference: Zodiacal Light and Interplanetary Medium, Honolulu, February 1967), who find wt=10+4 km/sec. Theoretical treatments by Weber and Davis (Astrophys. J. 147, 217,1967) and Modisette (J. Geophys. Res. 1967) indicate that part of the solar angular momentum is carried off in the magnetic stresses in the interplanetary magnetic field. The relative fractions are determined by the velocity structure of the solar wind near the sun; they are calculable from the observed azimuthal velocities and theoretical expressions. Typical parameters near the earth Wr=40O km/sec, wt=9 km/sec, Ne = 4/cm3, and Br =57 indicate that the solar angular momentum is lost nearly equally in particle motions and magnetic stresses and that the e-folding time for solar braking is 3-4X 10~ yr for a solar wind constant at its present value. If the solar wind has an independent e-folding time of 3 X 10~ yr, the initial sun could have had an equatorial rotational velocity 102 km/sec. Publication: The Astronomical Journal Pub Date: October 1967 DOI: 10.1086/110479 Bibcode: 1967AJ.....72R.787B full text sources ADS |