Suspended spicules associated with the enhanced bright network in an active region

Abstract

Abstract. The progressive rotation from the limb onto the disk of a long-lived cluster ofcoaligned He spicules was observed at high spatial resolution on the fringe of a large complex of activity. Although individual spicules were steadily changing, the organized cluster appeared consistently suspended above the photospheric limb when viewed in the wings of He ([A2[ ~ 0.9 ~). The phenomenon is the counterpart near an active region of the dark band discovered in the quiet low chromosphere by Loughhead (1969). But in the present circumstances the effect is perceived as a weakening of emission, i.e. as a gap rather than an obscuration. The initial gap between the off-band spicules and the photospheric limb narrowed and closed in about 4 h. A day later, the cluster of spicules could be identified at the same wavelength with a cluster of elongated dark mottles, similarly coaligned; they were adjacent to, but not in contact with, a foreshortened patch of faculae.The persistence of the gap in this cluster, and its occurrence in isolated spicules reported here in quiet regions, imply that the phenomenon is an inherent property of spicules. It is proposed that the gap results from a spicule-generating process initiated above the temperature minimum.

A Microfilament-Eruption Mechanism for Solar Spicules

“…• Gap at spicule bases. The sometimes-observed gap between the photospheric limb and the bottoms of spicules (e.g., Gaizauskas 1984) could result from the spire of the spicule forming by reconnection at the height of the neighboring bipole (Fig. 1).…”

What determines the radio polar brightening?

“…Nevertheless, there are discrete bright patches that can reach up to 40% above the quiet Sun brightness temperature, especially near the polar limb. It is known that there are no spicules over chromospheric plages (Shibata & Suematsu 1982;Zirin 1988) and the same behavior was observed for faculae (Gaizauskas 1984). Moreover, polar faculae and polar limb brightening are both anti-correlated with the sunspot cycle (Efanov et al 1980;Makarov & Makarova 1996;Koshiishi 1996;Selhorst et al 2003).…”

“…Therefore, we suggest that the discrete bright polar patches observed in 17 GHz maps are due to holes in the spicule forest right above polar faculae. Gaizauskas (1984) observed that there are no spicules over faculae as well as over plages (Zirin 1988). Moreover, faculae are known to be more abundant near the poles (Erofeev 2001;Unruh et al 1999;Ortiz et al 2002) and the radio polar bright regions are close to the polar faculae regions (Riehokainen et al 1998;Gelfreikh et al 2002).…”