The mean coronal magnetic field determined from HELIOS Faraday rotation measurements

Abstract

Coronal Faraday rotation of the linearly polarized carrier signals of the HELIOS spacecraft was recorded during the regularly occurring solar occultations over almost a complete solar cycle from 1975 to 1984. These measurements are used to determine the average strength and radial variation of the coronal magnetic field at solar minimum at solar distances from 3-10 solar radii, i.e., the range over which the complex fields at the coronal base are transformed into the interplanetary spiral. The mean coronal magnetic field in 1975-1976 was found to decrease with radial distance according to r-=, where ~ = 2.7 + 0.2. The mean field magnitude was 1.0 + 0.5 x 10-s tesla at a nominal solar distance of 5 solar radii. Possibly higher magnetic field strengths were indicated at solar maximum, but a lack of data prevented a statistical determination of the mean coronal field during this epoch.

VLA Measurements of Faraday Rotation through Coronal Mass Ejections

“…Several models employ two or three power law terms for the plasma density (e.g., see Pätzold et al 1987) or employ different model parameters depending on the region of the corona that is sampled (e.g., see Saito et al 1977). Similarly, the magnetic field is often represented by a dual power law in r, such as the sum of a dipole (∝ r −3 ) and interplanetary magnetic field term (∝ r −2 ) (Pätzold et al 1987;Mancuso & Spangler 2000;Kooi et al 2014). The exact form of the power laws assumed in Equations (6) and (8) Another simplification we made in modeling the background corona was assuming the coronal current sheet can be expressed as an infinitely thin magnetic neutral line where the polarity of the radial field reverses.…”

“…Examples of results which have been obtained with spacecraft transmitters are Stelzried et al (1970), Hollweg et al (1982), Pätzold et al (1987), Bird & Edenhofer (1990), Andreev et al (1997), Jensen et al (2013a,b), and Efimov et al (2015).…”

Nonlinear interaction of kinetic Alfvén waves and radio waves in the solar corona

“…As we mentioned in the beginning of this section, the magnetic field can vary in the range 0.5 < ∼ B 0 < 5 G, and the plasma density 1.8 × 10 6 < ∼ n 0 < ∼ 2 × 10 7 cm −3 at 1.5 − 2 R (Dulk & McLean 1978;Patzold et al 1987). Let as take: n 0 = 7 × 10 6 cm −3 , B 0 = 4 G from these ranges and the temperature T = 10 6 K. As can be seen in Fig.…”

Coronal Structures and Their Relation to the Solar Wind

“…1 and 2, two images of the corona obtained during the solar eclipses of June 30, 1973(RUSH, 1973) and February 16, 1980(DURST, 1982, respectively. The most striking impression obtained from Fig.…”