Evidence for non-radial fields in the Sun's photosphere and a possible explanation of the polar magnetic signal

Abstract

The appearance of the Ha fibrils suggests the presence of magnetic fields inclined at noticeably non-radial angles in the Sun's chromosphere. We present evidence to suggest that these angles continue into the photosphere.The presence even of small non-radial inclinations can significantly affect the appearance of regions observed by a longitudinal magnetograph. In particular, a simple bipolar loop can appear unbalanced when viewed near the limb. We suggest that the observed polar signal may be nothing more than a geometric effect arising when a balanced but systematically aligned array of bipolar pairs is viewed at an angle.

Association of Extreme-Ultraviolet Imaging Telescope (EIT) Polar Plumes with Mixed-Polarity Magnetic Network

“…A well-known characteristic of strong canopy fields is the appearance, toward the limb, of "false" polarities associated with the horizontal field component (Chapman & Sheeley 1968b;Pope & Mosher 1975;Giovanelli 1980). However, an inspection of the magnetograms in Figures 1-6 suggests that most of the black (white) features do in fact represent radially inward (radially outward) directed fields, for two reasons: first, we see little evidence for any systematic limbward "fringing" or black-white doubling of the flux elements, and, second, in those cases where a white (black) clump in 8542 has a black (white) clump on its limbward side, the 8688 magnetogram (which should be less susceptible to the fringing effect) shows that both polarities are present at lower heights.…”

Evaluating (and Improving) Estimates of the Solar Radial Magnetic Field Component from Line-of-Sight Magnetograms

“…inclined with respect to the local normal. This geometry can lead to the notorious introduction of apparent flux imbalance and "false" magnetic polarity inversion lines (see Figure 1) when the magnetic vector's inclination relative to the line-of-sight surpasses 90 • while the inclination to the local vertical remains less than 90 • or vice versa (Chapman and Sheeley, 1968;Pope and Mosher, 1975;Giovanelli, 1980;Jones, 1985). Although this artifact can be cleverly used for some investigations (Sainz Dalda and Martínez Pillet, 2005) it generally poses a hindrance to interpreting the inherent solar magnetic structure present.…”