Big brother

The imagery underneath covers the period from 22 November until 23 November at noon and shows the Sun in white light (SDO/HMI). It shows a sunspot region (NOAA 2784) decaying in the northern solar hemisphere, another region developing in the trailing portion of NOAA 2783 in the southern hemisphere, and two sunspot regions rotating over the southeast solar limb (lower left). The first one starts appearing early on 22 November and was numbered NOAA 2785, whereas its big brother starts becoming visible early on 23 November and still needs to receive a number. In particular this latter group is impressive, while it still has not fully rotated over the solar limb yet. It currently consists of a big single sunspot which has a diameter of 3 degrees, corresponding to nearly the circumference of the Earth.


Space weather forecasters were alerted well ahead. Indeed, during the last few days, they saw a substantial increase in the number of coronal mass ejections (CMEs) emanating from behind the southeast limb (see CACTus). Moreover, flaring activity was observed from sources beyond the southeast limb as early as 20 November, with the source regions still 1-2 days before rounding the solar limb. See the white light and Extreme Ultraviolet (EUV) images from the Solar Dynamics Observatory underneath.

The final clues were given by the STEREO-A spacecraft, which currently trails the Earth by 58 degrees and so had a good view on a part of the solar farside. EUV images clearly showed two bright and flaring active regions in the southern hemisphere. The coronagraphic image on the right (SOHO/LASCO) shows the (weak) CME associated with the 20 November flaring from the two regions.

Both sunspot groups currently seem to have a simple magnetic configuration, and they also seem to be a bit less flare-active compared to the previous days. Nonetheless, with such a big spot flaring activity may pick up relatively fast. As days go by and the sunspot groups approach the central meridian, any associated CME may become earth-directed.  




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