Enhanced Rieger Type Periodicities; detection in X-ray solar flares and statistical validation of Rossby waves existence

M. Dimitropoulou¹, X. Moussas¹, D. Strintzi²

¹University of Athens, Greece
²National Technical University of Athens, Greece

The known Rieger Periodicity (ranging in literature from 150 up to 160 days) is obvious in numerous solar indices. Many sub-harmonic periodicities have also been observed (128-, 102-, 78-, and 51 - days) in flare, sunspot, radio bursts, neutrino flux and flow data, coined as Rieger Type Periodicities (RTPs). Several attempts are focused to the discovery of their source, as well as the explanation of some intrinsic attributes that they present, such as their connection to extremely active flares, their temporal intermittency as well as their tendency to occur near solar maxima. In this paper, we link the X-ray flare observations made on Geosynchronous Operational Environmental Satellites (GOES) to an existing theoretical model (Lou 2000), suggesting that the mechanism behind the Rieger Type Periodicities is the Rossby Type Waves. The enhanced data analysis methods used in this article (Scargle-Lomb periodogram and Weighted Wavelet Z-Transform) provide the proper resolution needed to argue that RTPs are present also in less energetic flares, contrary to what has been inferred from observations so far.