Institution: | a Nuclear and Particle Physics Section, Physics Department, Athens University, Pan/polis, 15771, Athens, Greece b Astrophysics, Astronomy and Mechanics Section, Department of Physics, Athens University, Panepistimioupolis, 15783, Athens, Greece c Research Center for Astronomy and Applied Mathematics of Athens Academy, Anagnostopoulou 14, 10673, Athens, Greece d Institute of Nuclear Physics, Moscow State University, 119899 Vorobievy Gory, Moscow, Russia |
Abstract: | A statistical analysis of the cosmic-ray intensity (CR) daily means, registered at three Neutron Monitor stations with different cut-off rigidities (Deep River, Climax and Alma-Ata), as well as, of the solar hard X-ray flares fluence recorded by Venera-13, -14 space-probes, has been performed for the time interval 1981–1983. Various methods of time series spectrum analysis, such as Fast Fourier Analysis (FFT) and Maximum Entropy (MESA), accompanied by appropriate statistical tests, have been employed to detect periodicities, while the method of Successive Approximations (SA) is used independently in order to define the amplitude and the phase of each fluctuation. New short-term periodicities of 100, 70, 50 and 32 days, in addition to the known ones of 152, 27 and 14 days, appeared in cosmic ray data. During this particular time interval, similar spectral behaviour has been reported in the solar hard X-ray flares data. The influence of the solar hard X-ray flares variability in the energy range 50–500 keV, expressed by their fluence values, upon the cosmic-ray modulation, is discussed. |