Purely coronal flare-like variations

A detailed study of the quasi-periodical post-flare variations on November 6, 1980 in X-rays, UV lines, microwaves, and metric waves confirms that these variations were predominantly thermal phenomena and occurred solely in the corona. Only the short-lived impulsive components that preceded all or most of the individual variations were of non-thermal character and penetrated down to the transition layer. The chromosphere (in Hα) did not participate in any part of these events, in contrast to a flare that appeared at the same place a few hours later. However, the X-ray emission of these variations was so strong that the transition layer and the chromosphere definitely should have been enhanced through heat conduction along the magnetic field lines. The expected heat flux at the top of the chromosphere coming from some of these coronal brightenings was 60–80% of the flux expected in the flare at 17:26 which gave rise to a 2B flare in Hα (Figure 8). Therefore, we suggest that the variations were produced in a coronal plasmoid with closed field lines completely detached from the lower atmospheric layers (Figure 9b). We also give reasons why such a detached plasmoid can be expected to be formded in the very late phase (some 4–5 hr after the onset) of a major two-ribbon flare.