The fingerprint of the new solar cycle
posted: Dec 14, 2009
The new solar activity cycle still puzzles all solar physicists due to its very slow start. The sunpot index for November 2009 is still only 4.2, well below many predictions (SIDC predictions: SM=6, CM=13). Although, the number of spotless days decreased strongly compared to the last two years, with multiple but small sunspot groups.

Taking a closer look at the spotless intervals, we find that over the last 8 Carrington rotations, the active regions were systematically concentrated in fairly narrow longitude intervals, which are different for each solar hemisphere. For the Northern hemisphere, 8 regions out of 10 emerged between 200 and 300 longitude (width: 100), including the three largest ones. For the Southern hemisphere, 6 regions out of 9 all appeared in the narrow interval 0 - 50 (width: 50), and the other 3 in the interval 180-250 (width 70), which matches the Northern active interval (the largest active region in the Southern hemisphere was at 250 longitude).

The manifestations of the nascent solar cycles are thus quite asymmetrical, with more than 80% of the active regions concentrated over less than one third of the circumference of the Sun. This persistent spatial "fingerprint" probably carries useful information for the modelling of the solar dynamo and the physics of magnetic flux emergence in the Sun. Indeed, the solar cycle is more than just a time series. It is also an evolving along all three spatial dimensions. As the cycle unfolds, we expect that the current pattern will progressively drift in longitude, just as it does in latitude, giving us precious hints about the internal mechanism of this "lymphatic" cycle.
USET images of the two largest sunspot groups of the last 8 months: AR #11024 imaged on 6/7/2009 (long: 250) and AR #11029 imaged on 28/10/2009 (long: 215).
Click on the images for a larger view.
USET real-time images are available on-line from http://www.sidc.be/uset.
Author: F. Clette