Global analysis of active longitudes of solar X-ray flares

There is increasing evidence that various manifestations of solar activity are non-axisymmetric and mainly occur in two preferred longitude ranges, so called active longitudes. We have earlier analyzed the longitudinal occurrence of solar X-ray flares observed by GOES satellites using a specially developed dynamic, differentially rotating coordinate system. In this frame, the longitude distribution shows two persistent preferred longitudes separated by about 180 degrees whose strength alternates in time according to the so called flip-flop phenomenon. Here we make the first global statistical analysis to find the best fitting values for parameters describing the differential rotation of active longitudes of X-ray flares. We find that the new analysis greatly improves the earlier values for the rotation parameters, making them consistent between the three different classes of X-ray flares. The improved parameters also yield a systematically higher level of non-axisymmetry for the longitudinal distribution, thus increasing the statistical significance of the existence of active longitudes. Accordingly, a significant amount of X-ray flares of different classes are produced by the same two active longitudes. We also find a significant difference between the rotation rates in the two solar hemispheres, with active longitudes rotating faster than the Carrington rate in the northern hemisphere and slower than the Carrington rate in the southern hemisphere.