The magnetic fields of active regions

✍ Scribed by Robert F. Howard

• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 663 KB
• Volume: 135
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00146697

✦ Synopsis

The Mount Wilson coarse array magnetograph data set is analyzed to determine characteristics of magnetic regions as a function of distance from the average latitude, ~o, of regions in each hemisphere, a quantity which varies during the activity cycle. Regions with normal polarity axis orientations are distributed asymmetrically about Co with the median latitude about 1 deg equatorward of s Reversed polarity orientation regions show a somewhat broader and more symmetric distribution. Average sizes for regions at ~ = 0 (Co) are nearly twice as large as those located at 10 deg latitude in either direction. Regions poleward of Co tend to show a net magnetic field biased toward the following polarity, and regions equatorward of Co are biased toward the leading polarity, both by around 10 %. Neither region growth rates nor decay rates are related to ~. The average polarity axis tilt angles of regions are lower for regions near the equator than for those nearer the poles. It is most likely that this is basically an effect of latitude rather than ~. Meridional motions of young regions are shown to be toward ~o. Older regions do not show this behavior. This may be a magnetic effect rather than being due to large-scale circulatory motion, as has been suggested in the past. East-west inclination angles of active region magnetic fields show a slight tendency to trail the rotation direction (eastward inclination) by a few deg for regions with ~ > 0 and lead the rotation (westward inclination) by a few deg for regions with r > 0. This effect may be related to the torsional oscillations. These various results are discussed in terms of a hypothetical subsurface magnetic flux tube which gives rise to the surface activity.