24 synoptic maps of average magnetic field in 296 prominences measured by the Hanle effect during the ascending phase of solar cycle 21

V Bommier,J L Leroy,S Sahal-Bréchot

doi:10.1051/0004-6361/202038868

Abstract

Aims. We present 24 synoptic maps of solar filaments, in which the average unambiguous magnetic field vectors of 296 prominences were determined with Pic-du-Midi observations between 1974 and 1982. This was the ascending phase of cycle 21. Methods. The magnetic field was determined by interpreting the Hanle effect, which is observed in the He I D3 line. Previous results for the prominence field polarity and prominence chirality were applied to solve the fundamental ambiguity. The measurements were averaged in each prominence for accuracy reasons. Results. The result is twofold. First, alternating field directions can be observed from one neutral line to the next. Second, a general field alignment is found along a solar north-south field that is distorted by the differential rotation effect.

Highlights

The first application of the Hanle effect (Hanle 1924, 1991) to magnetic field measurements of solar prominences has been made by Hyder in a seminal paper (Hyder 1965), after a theoretical investigation by Öhman (1929), who showed that the radiation emitted by prominences observed at the limb are linearly polarized by the radiative scattering of the incident solar radiation
Hyder (1965) summarized all these observations in his Fig. 1, which shows that the linear polarization directions observed by Lyot are rotated with respect to the solar limb
We publish the synoptic maps of the solar filaments, on which we have reported the 296 prominence average magnetic field vectors

Summary

Introduction

The first application of the Hanle effect (Hanle 1924, 1991) to magnetic field measurements of solar prominences has been made by Hyder in a seminal paper (Hyder 1965), after a theoretical investigation by Öhman (1929), who showed that the radiation emitted by prominences observed at the limb are linearly polarized by the radiative scattering of the incident solar radiation. Hyder (1965) summarized all these observations in his Fig. 1, which shows that the linear polarization directions observed by Lyot are rotated with respect to the solar limb. Hyder assigned this rotation of the polarization direction to the Hanle effect, as suggested by Öhman (1929). The rotation of the scattering linear polarization direction is one of the main features of the Hanle effect

Methods

Findings

Discussion

Conclusion