Friday, 26 July 2013

AR11785

Watching big spot groups develop in both while light (the continuum) and H-alpha (hydrogen emission band) hints at the magnetic complexity of sunspots. Add the umbral magnetic field data posted daily by Mt Wilson Observatory (c) Regents of the University of California, and we have enough material for a PhD! Understanding current spots is further complicated by the steady weakening of spot magnetic fields. Late 20thC authors all agreed that average sunspot fields were 3000G - well, they arent any more! They currently average <2000G, and falling. And the Mt Wilson archive published in 2006 (Livingston, Harvey et al, "Sunspots with the Strongest Magnetic Fields" Sol. Physics) of a century of umbral field data showed clearly that the era of 3000G fields was short-lived: from ~1950 to 1992.
   Translation: current spots are pale and small in area compared with earlier decades. Nevertheless, spot groups like this one showed interesting details and some nice surges on the western edge of the preceding spots. Sadly, this group had no flares stronger that GOES C9. A glance at the bargraph below shows that SC24 flaring, so far, is well behind that of the past three cycles - with no sign of a dramatic turn-around any time soon.
    Southern group AR11785 had an irregular separation of spots with unlike polarities, making it Hale magnetic class Beta-Gamma; we would have expected much stronger flaring. Watch the site when it returns around July 30 - will any spots remain? Or maybe just a large patch of H-alpha plage with some filaments.

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