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

TL;DR

This study presents 24 synoptic maps of magnetic fields in 296 solar prominences during solar cycle 21's ascending phase, revealing alternating field directions and a general north-south alignment influenced by differential rotation.

Contribution

It provides the first comprehensive synoptic magnetic field maps of prominences during this solar cycle phase using Hanle effect measurements and resolves fundamental ambiguities in magnetic field direction.

Findings

Alternating magnetic field directions observed between neutral lines.

A general north-south magnetic field alignment distorted by differential rotation.

Numerical data of prominence magnetic fields provided as online material.

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 \ion{He}{i} D$_3$ 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. The numerical data for the prominences and their magnetic field coordinates are provided as online material associated with this paper.