On the location of solar active longitudes

Abstract

The longitudinal distributions of sudden ionospheric disturbances producing active regions with high flare activity and/or with at least one high energy flares particle event (PCA or GLE) have been examined. These active regions appear to cluster at four active longitudes, separated by a longitudinal distance of about 60° and 180°. It is also inferred that these active longitudes drift in position by about 21.55° per year, thus exhibiting almost rigid rotation. Quasi-periodicities of 2.3 to 5.3 yr are also seen in 12 Fourier spectra of times series of high flare activity regions in 30° wide longitude range. These periodicities have been interpreted as due to drifting of four active longitudes having 60° and 120° longitudinal separations.