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

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.