A Statistical Study on Solar Active Regions Producing Extremely Fast Coronal Mass Ejections
Abstract
We present a statistical result on the properties of solar source regions that have produced 57 fastest front-side coronal mass ejections (CMEs) (speed 1500 km/s) occurred from 1996 June to 2007 January. The properties of these fast-CME-producing regions, 35 in total, are compared with those of all 1143 active regions (ARs) in the period studied. An automated method, based on SOHO/MDI magnetic synoptic charts, is used to select and characterize the ARs. For each AR, a set of parameters are derived including the areas (positive, negative and total, denoted by AP, AN and AT respectively), the magnetic fluxes (positive, negative and total, FP, FN and FT respectively), the average magnetic field strength (Bavg), quasi-elongation (e) characterizing the overall shape of the AR, the number and length of polarity inversion lines (PILs, or neutral lines, NPIL and LPIL respectively), and the average and maximum of magnetic gradient on the PILs (GOPavg and GOPmax respectively). Our statistical analysis shows a general trend between the scales of an AR and the likelihood of producing a fast CME, i.e., the larger the geometric size (AT), the larger the magnetic flux (FT), the stronger the magnetic field (Bavg), and/or the more complex the magnetic configuration (NPIL and LPIL), then the higher the possibility of producing a fast CME. When all ARs are sorted into three equally-numbered groups with low, middle and high values of these parameters, we find that, for all these AR parameters, more than 60% of extremely fast CMEs are from the high-value group. The two PIL parameters are the best indicators of producing fast CMEs, with more than 80% from the high value group.
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