Birth and death of an active region

Solar Dynamics Observatory

Active regions appear on the solar surface as dark bipolar structures that grow rapidly and separate from each other, giving rise to fully fledged sunspots and numerous pores that change and merge with each other continually. The two main spots of active regions have opposite magnetic polarities. They are called leader and follower according to their position relative to the direction of solar rotation. Vigorous magnetic flux emergence occurs during the early phases of the formation of active regions. This emerging flux can be detected in continuum intensity images, but is best seen in circular polarization maps (or magnetograms).

The movie shows the full evolution of AR 11267 during its disk passage over the course of 7 days in August 2011. The observations were taken by the HMI instrument on the Solar Dynamics Observatory. The left panel shows the solar surface in continuum intensity, while the right panels shows the corresponding magnetograms. The magnetograms reveal the existence of magnetic fields that are not visible in continuum intensity. White represents magnetic fields pointing towards us, while black represents fields pointing away from us. Note that the leader spot (the rightmost one) and the network of small magnetic elements surrounding it have positive polarity, while the follower part of the active region has negative polarity.

The active region appears very quickly and form spots in less than 12 hours. The spots develop ever-changing penumbral sectors. This is a relatively small active region with a low magnetic flux content, so the spots never reach a large size. They attain their maximum extent about 1 day after they show up on the surface. From that point on, the spots start to disappear, a process that takes about 2.5 days. The leader spot is always more stable than the follower. When the spots are no longer visible in continuum intensity, the magnetograms still show the presence of magnetic fields in the area, with positive polarity in the leading part and negative in the follower part. These active region remnants are believed to be the main source of flux for the photospheric network.

Download the movie clicking HERE

Movie credit: Aimee Norton (Stanford University)

Text credit: Luis Bellot Rubio (IAA-CSIC)

Observations by HMI onboard SDO (NASA)