NOAA Active Region Designations

If you’ve noticed that NOAA 11135 from 2010 December 14 lacked sunspots, you may be wondering why it was designated an active region number by the NOAA.

Per the NOAA Glossary, the NOAA defines an active region as:

A localized, transient volume of the solar atmosphere in which plages, sunspots, faculae, flares, etc., may be observed. Active regions are the result of enhanced magnetic fields; they are bipolar and may be complex if the region contains two or more bipolar groups.

A region number is defined as:

A number assigned by NOAA to a plage region or sunspot group if one of the following conditions exists: (1) the region is a group of at least sunspot classification C; (2) two or more separate optical reports confirm the presence of smaller spots; (3) the region produces a solar flare; (4) the region is clearly evident in H-alpha and exceeds 5 heliographic degrees in either latitude or longitude. (See also active region.)

In the case of NOAA 11135, it flared a few days ago. That in itself was enough to warrant designating a number for that region. Solar observer Thomas Ashcraft caught it superbly in his thread Flare at northeast limb now 1849 ut Dec 12, 2010

There were a few eruptions on the 12th. For another look at the activity on the 12th: Triple CME gif from SOHO


~ by Erika Rix on December 15, 2010.

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