Extraction of Halo Coronal Mass Ejection Asymmetry Information from LASCO Coronagraph Images

Abstract

A method for quantifying the asymmetry attributes of coronal mass ejections (CMEs) is described. The technique developed is applied to a set of full-halo CMEs observed from 1997 to the end of 2000 by the Large Angle Spectrometric Coronagraph (LASCO) instrument on board the Solar and Heliospheric Observatory (SOHO) spacecraft. A cross section of events is examined, with the progression of asymmetry characteristics as the ejecta proceeds outward illustrated for a symmetrical full-halo CME, an asymmetrical full-halo CME, and multiple CMEs. A control sample for a day with minimal solar activity is presented for comparison. A qualitative evaluation of the results with visual inspection of the coronagraph data is discussed. Relationships between the asymmetry parameters derived from the data are examined, and good correlations are found among the asymmetry magnitudes, the average sector pixel intensities, and the frontal CME speeds. This computerized method can also be designed to automatically detect and measure the asymmetry and relative brightness of any CME. We compare the results with storms at Earth to demonstrate that the calculated asymmetry magnitude by itself indicates the geoeffectiveness of a CME, with any associated solar surface activity helping to determine whether the CME is aimed Earthward or not. Thus, this test suggests that our technique is useful as a forecast tool for space weather applications. With modifications, the algorithm is applicable to analyses of the data returned from the Solar Mass Ejection Imager (SMEI) aboard the Coriolis spacecraft and the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) coronagraph and heliospheric imagers aboard the two Solar Terrestrial Relations Observatory (STEREO) spacecraft.