Characteristics of Anemone Active Regions Appearing in Coronal Holes Observed with {\it Yohkoh} Soft X-ray Telescope

TL;DR

This study characterizes active regions in coronal holes observed with Yohkoh's Soft X-ray Telescope, highlighting their 'sea-anemone' shape, magnetic polarity patterns, and asymmetrical X-ray brightness, indicating simpler magnetic structures.

Contribution

It provides the first detailed analysis of anemone-shaped active regions in coronal holes, revealing their magnetic polarity consistency and brightness asymmetry, and compares their magnetic complexity to other regions.

Findings

Approximately 25% of active regions in coronal holes are anemone-shaped.

Anemone ARs follow Hale-Nicholson's polarity law.

Anemone ARs exhibit east-west brightness asymmetry.

Abstract

Coronal structure of active regions appearing in coronal holes is studied by using the data obtained with the Soft X-Ray Telescope (SXT) aboard {\it Yohkoh} from 1991 November to 1993 March. The following characteristics are found; Many of active regions appearing in coronal holes show a structure that looks like a ``sea-anemone''. Such active regions are called {\it anemone ARs}. About one-forth of all active regions that were observed with SXT from their births showed the anemone structure. For almost all the anemone ARs, the order of magnetic polarities is consistent with the Hale-Nicholson's polarity law. These anemone ARs also showed more or less east-west asymmetry in X-ray intensity distribution, such that the following (eastern) part of the ARs is brighter than its preceding (western) part. This, as well as the anemone shape itself, is consistent with the magnetic polarity distribution around the anemone ARs. These observations also suggest that an active region appearing in coronal holes has simpler (less sheared) and more preceding-spot-dominant magnetic structure than those appearing in other regions.