Solar flare activity was not particularly impressive last week, with no C-class events at all. Fortunately, a B7.9 flare peaking at 03:23UT on 09 September in active region NOAA 2588, was associated with a lovely post-flare effect: the disappearance of almost an entire filament about 10 degrees to the southeast of this active region.
Solar filaments are clouds of ionized gas above the solar surface squeezed between magnetic regions of opposite polarity. Being cooler and denser than the plasma underneath and their surroundings, they appear as dark lines when seen on the solar disk using special filters, such as Hydrogen-alpha (H-alpha; 656.28 nm). These structures only survive by the stability of the surrounding magnetic fields. Hence, the B7 event in NOAA 2588 did not only produce electromagnetic radiation, it apparently also created an imbalance in the magnetic fields. As a result, about an hour after the B7 flare, first the middle portion and then the western portion of the nearby filament disappeared entirely from view in H-alpha. This can be seen in the imagery underneath. The 40-degrees long filament to the upper right remained unchanged. The H-alpha imagery is courtesy of NSO's GONG H-alpha Network.
