A high-latitude sunspot group
posted: January 30, 2014

It is a well-known feature of the solar cycle that its first sunspot groups appear at high solar latitudes. These sunspots appear a few months prior to the solar cycle minimum around 30 degrees away from the solar equator. As the solar cycle progresses, the sunspot groups gradually appear closer to the solar equator, with -during maximum- a heliographic latitude of about 15 degrees. As the solar cycle heads for the next minimum, the sunspot groups appear even closer to the solar equator, gradually becoming smaller and disappearing while the sunspots of the new solar cycle manifest themselves again at high latitudes. The evolution can be seen in images underneath for solar cycle 23 (SOHO/MDI: June 1998, 2001, and 2004).


This movement of sunspots can also be followed in a diagram showing the latitude of sunspot groups over time. As it resembles the wings of a butterfly, it is called a butterfly-diagram. The first such diagram was published by Walter Maunder (yes, the guy from the "Maunder Minimum"!) in the early 1900's. More than 100 years later, it is believed this butterfly-diagram is a manifestation of the solar dynamo, but the precise mechanism still eludes scientists.


Nearly 95% of all sunspot groups appear in a belt extending 30 degrees on each site of the solar equator, and nearly three quarters appear within 20 degrees of the solar equator. For the ongoing solar cycle, this was not different. Only a handful of spots had a latitude of more than 35 degrees. NOAA 11069, a reasonably sized sunspot group that appeared in May 2010, has the highest latitude with +41 degrees.


On the southern hemisphere, not a single sunspot group with a latitude over 35 degrees had been observed so far. That changed last week, with the appearance of NOAA 11962 attaining a latitude of -37 degrees. It is not uncommon that at this phase (maximum) of the solar cycle, sunspot groups still appear at these high latitudes. Also, they are not necessarily small and inactive. An extreme example is NOAA 6659 which appeared in June 1991. This sunspot region was one of the largest and most flare active regions of solar cycle 22, and had a respectable latitude of +31 degrees.


Credits - Data and imagery for the movie clips were taken from SDO, SOHO, USET, and Solar Monitor.