Letter to the Editor

Transient horizontal magnetic fields in solar plage regions

¹ Department of Astronomy, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan e-mail: ryoko.ishikawa@nao.ac.jp
² National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³ Department of Earth and Planetary Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁴ High Altitude Observatory, National Center for Atmospheric Research, PO Box 3000, Boulder CO 80307-3000, USA
⁵ Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto 607-8471, Japan
⁶ ISAS/JAXA, Sagamihara, Kanagawa 229-8510, Japan
⁷ Lockheed Martin Solar and Astrophysics Laboratory, B/252, 3251 Hanover St., Palo Alto, CA 94304, USA

Received: 8 November 2007
Accepted: 21 December 2007

Abstract

Aims.We report the discovery of isolated, small-scale emerging magnetic fields in a plage region with the Solar Optical Telescope aboard Hinode.

Methods.Spectro-polarimetric observations were carried out with a cadence of 34 s for the plage region located near disc center. The vector magnetic fields are inferred by Milne-Eddington inversion.

Results.The observations reveal widespread occurrence of transient, spatially isolated horizontal magnetic fields. The lateral extent of the horizontal magnetic fields is comparable to the size of photospheric granules. These horizontal magnetic fields seem to be tossed about by upflows and downflows of the granular convection. We also report an event that appears to be driven by the magnetic buoyancy instability. We refer to buoyancy-driven emergence as type 1 and convection-driven emergence as type 2. Although both events have magnetic field strengths of about 600 G, the filling factor of type 1 is a factor of two larger than that of type 2.

Conclusions.Our finding suggests that the granular convection in the plage regions is characterized by a high rate of occurrence of granular-sized transient horizontal fields.