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Astron. Astrophys. 319, L13-L16 (1997)

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Letter to the Editor

On the origin of sunspots

Alexander Ruzmaikin

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA and San Fernando Observatory, California State University, Northridge

Received 10 January 1997 / Accepted 21 January 1997


It is proposed that sunspots (and other flux emergence phenomena) originate due to the presence of fluctuating magnetic fields in addition to the regular, mean field in the convection zone. The mean field predicted by dynamo theories is too weak by itself to emerge at the surface of the Sun. However, the same dynamo processes that produce the mean field also produce fluctuating fields. It is suggested here that magnetic fields emerge at the solar surface at those random times and places when the total magnetic field (mean field plus fluctuations) exceeds the threshold for buoyancy. In this way the mean field is responsible for observed regularities of the sunspot magnetic fields, such as the Hale's law and the 11-year periodicity, and the fluctuations are responsible for emergence of the magnetic field of individual sunspots. A simple illustrative model calculation of a series of "sunspot cycles" is presented. The model spectrum compares well with the observed spectrum of sunspots.

Key words: Sun: sunspots – Sun: random magnetic fields

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998