Coronal White-Light Jets near Sunspot Maximum

摘要

During the 1996-1997 activity minimum, the Large Angle and Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) recorded numerous jetlike ejections above the Sun's polar regions. In a previous study, we showed that these white-light ejections were the outward extensions of extreme-ultraviolet (EUV) jets, which in turn originated from flaring bright points inside the polar coronal holes. Here we investigate a number of jetlike events observed with LASCO during the current sunspot maximum. To identify the solar surface counterparts of these events, we again use Fe XII λ195 images obtained by the EUV Imaging Telescope on SOHO. The white-light jets in our sample have angular widths of ~3°-7° and velocities typically of order 600 km s-1; they tend to be brighter and wider than the polar jets observed near sunspot minimum and are distributed over a much greater range of latitudes. Many of the ejections are recurrent in nature and originate from active regions located inside or near the boundaries of nonpolar coronal holes. We deduce that the jet-producing regions consist of systems of closed magnetic loops partially surrounded by open fields; perturbations in the closed fields caused them to reconnect with the overlying open flux, releasing the trapped energy in the form of jetlike ejections. In some events, the core of the active region erupts, producing fast, collimated ejections with widths of up to ~15°.