  Solar flare emissions in the chromosphere often appear as elongated ribbons
on both sides of the magnetic polarity inversion line (PIL), which has been
regarded as evidence of a typical configuration of magnetic reconnection.
However, flares having a circular ribbon have rarely been reported, although it
is expected in the fan--spine magnetic topology involving reconnection at a
three-dimensional (3D) coronal null point. We present five circular ribbon
flares with associated surges, using high-resolution and high-cadence halpha
blue wing observations obtained from the recently digitized films of Big Bear
Solar Observatory. In all the events, a central parasitic magnetic field is
encompassed by the opposite polarity, forming a circular PIL traced by filament
material. Consequently, a flare kernel at the center is surrounded by a
circular flare ribbon. The four homologous jet-related flares on 1991 March 17
and 18 are of particular interest, as (1) the circular ribbons brighten
sequentially, with co-spatial surges, rather than simultaneously, (2) the
central flare kernels show an intriguing "round-trip" motion and become
elongated, and (3) remote brightenings occur at a region with the same magnetic
polarity as the central parasitic field and are co-temporal with a separate
phase of flare emissions. In another flare on 1991 February 25, the circular
flare emission and surge activity occur successively, and the event could be
associated with magnetic flux cancellation across the circular PIL. We discuss
the implications of these observations combining circular flare ribbons,
homologous jets, and remote brightenings for understanding the dynamics of 3D
magnetic restructuring.
