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 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.

Observations key to understanding solar cycles: a review

“…Reproduced in Figure 12 is a synoptic chart from the Meudon Observatory with the directions of the magnetic field superposed by Bommier et al (2021). These synoptic charts refine and summarize the original work in Bommier et al (1985) and references therein. Figure 12 shows the magnetic field directions for the polar crown and subpolar crown filaments for solar rotation no.…”

“…In this author's awareness, there is only one group of closely related phenomena that yields a positive answer to this question. Well-documented in the literature, these phenomena are polar crown filaments, subpolar crown filaments, and their filament channels (Rust, 1967;Leroy, 1978;Bommier et al, 1985;Leroy, 1988;Martin, 1990;Bommier et al, 2021). Understanding how and why the polar crown filaments and subpolar crown filaments develop opposite east-to-west and west-to-east directions every 11 years requires at least a minimal understanding of both their evolution and the creation of the direction of the magnetic fields along filament channels and filaments.…”

“…The opposing east-to-west or west-to-east directions of the polar crown and subpolar crown filaments were initially recognized in articles by Rust (1967), ), Bommier et al (1985, and Martin (1990). Reproduced in Figure 12 is a synoptic chart from the Meudon Observatory with the directions of the magnetic field superposed by Bommier et al (2021). These synoptic charts refine and summarize the original work in Bommier et al (1985) and references therein.…”

“…This led to recognizing that the alternating direction of the polar and subpolar crown filaments is due to the alternating bands of the decayed remnants of active regions that have evolved into north-to-south tiers in latitude (Leroy, 1978;Leroy et al, 1984;Bommier and Leroy, 1998). The solar cycle reversals of the direction of the magnetic field along filaments in both hemispheres are simply due to the poleward migration of alternating tiers of positive and negative magnetic fields at high latitudes that are well explained in Bommier et al (2021). This synoptic chart of active regions and filaments for the whole of solar rotation no.…”

“…Photospheric magnetic fields are represented by red, + symbols for positive magnetic fields, and green − symbols for negative fields. These background polarities and the polarity boundaries (in green) have been added from McIntosh maps (NOAA/SEC) by Bommier et al (2021) along with the red arrows which are proportional to the magnetic fields in the filaments. Polar crown filaments along the polar crown magnetic field boundaries in the northern and southern hemispheres are seen to be opposite in their west-to-east and east-to-west magnetic field directions.…”