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

Coronal structure of active regions appearing in coronal holes is studied by using the data obtained with the Soft X-Ray Telescope (SXT) aboard 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 anemone ARs. About oneforth 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. Subject headings: Sun: activity — Sun: corona — sunspots — Sun: X-rays, gamma rays 1 Nobeyama Solar Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano, 384-1305, JAPAN 2 National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo, 181-8588, JAPAN 3 The Graduate University for Advanced Studies (SOKENDAI), JAPAN 4 Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto, 607-8471, JAPAN 5 Lockheed Martin Solar and Astrophysics Laboratory, Department/ADBS, B/252, 3251 Hanover Street, Palo Alto, CA 94304, U.S.A.