A Search for Precursor Activity Associated with Coronal Mass Ejections, Using White-Light Coronagraph Observations Obtained with the SOLWIND Instrument on Board the Air Force P78-1 Satellite.
Final rept. 15 Sep 84-31 Dec 85,
NAVAL RESEARCH LAB WASHINGTON DC
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Large-scale coronal disturbances preceding solar flares or other surface activity and resulting in mass ejection, are perhaps the most intriguing and least understood manifestations of preflarepre mass ejection activity. The existence of energetic disturbances in the corona significantly before the associated surface events has profound implications for the location and mechanism of preflare energy storage, as well as the evolution and magnitude of the energy release or magnetic disequilibrium characterizing the interval before and during the mass ejection. A systematic search for forerunners is performed using the white light coronagraph observations obtained with the WOLWIND instrument on board the P78-1 satellite. 44 bright, well observed events are selected and analyzed. In comparing the SOLWIND difference images to the excess mass contours, we find that the 2 sigma contour level used to define the forerunner front is readily apparent in the images. In fact, this level generally outlines the leading edge of the visible event. If the contour plots of the SOLWIND events are made with the same linear contour spacing, a forerunner plateau is visible in both the CME itself and nearby affected coronal features, e.g., a neighboring streamer that has been pushed aside. If contour levels with power law spacing similar to the density distribution of the background corona are chosen, however, the forerunner plateau disappears. Therefore, we conclude that the forerunner phenomenon is an integral part of the CME itself and not a manifestation of precursor activity.