Longitudinal distribution of major solar flares during 1975–2005 Original Research Article

We have analyzed the coordinates of optical flares associated with the X-ray flares of class X observed by GOES satellite during the period from January 1975 through September 2005. The results can be summarized as follows. 1. The latitude distribution of X-ray flares of class X displays the Maunder butterfly diagram pattern. 2. The longitude distribution suggests that the place where X-ray flares of class X preferentially occur migrates in Carrington longitude. 3. In the new dynamic reference frame inferred from the differential rotation law on the Sun, the longitude distribution diagram shows that there are two persistent preferred longitudes of strong X-ray flare occurrence separated by about 180°. This suggests that strong X-ray flare active longitudes exist indeed for tens of years. 4. The strength of the two active longitudes alternates similarly to the “flip–flop” phenomenon. 5. The non-axisymmetry of the X-ray flare distribution is found to be highly significant 42.5% (43.0%) for Northern (Southern) hemisphere for the peak intensity and 55% (49%) for Northern (Southern) hemisphere for the flare number.