July 2012 was one of the most active months so far this solar cycle, producing numerous medium and strong solar flares. Unfortunately, since then, solar flare activity has not been particularly exciting. In December, things went from bad to worse, with only a few dozen small ("C") flares and no medium ("M") flares at all. The previous month with no M-flares was December 2010. Also, the last M-flare dates back to 28 November 2012 (M2 in NOAA 1620), and the last extreme flare (X-class) occurred on 23 October 2012 (X1 in NOAA 1598). It seems ages ago!
During such gloomy times, even a small flare can make solar observers happy. The Christmas flare in NOAA 1635 was such a fine example. This C4-flare occurred in a modest and not very complex sunspot group. The blue dot on the SDO white light image represents the Earth for comparison.
A short movie was created from SDO-imagery, first showing the active region in white light (SDO/HMI) and then the eruption itself (SDO/AIA-171). The two subsequent clips show the same eruption, but using a transparent layover in white light and a magnetogram. This allows for a better view on which sunspots and magnetic areas were involved in this flare.
Clearly, one can see that the flare took place in the leading (right) part of the sunspot group, along the magnetic inversion line (red dashed - see image above), between negative polarity ("black") sunspots and positive ("white") polarity areas with no or very small sunspots. Interestingly, one foot point of the subsequent coronal loops was anchored in the *trailing* portion of the active region (bottom left, south of the trailing sunspots - see image below), suggesting some magnetic restructuring took place.
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