Time variability of the Rome cosmic ray intensity

Abstract

The time variability of the Rome neutron monitor data (SVIRCO Observatory: INAF/IFSI-Roma and UNIRo- maTre collaboration; rigidity threshold about 6.3 GV) from 1964 to 2004 was analyzed by using the Empirical Mode Decomposition (EMD) technique. Two prominent scales of variability have been identified: the ∼ 11-yr (Schwabe) cycle and the quasi biennial oscillations (QBOs). It is shown that the superposition of the two waves reproduces fairly well the long-term trend of the SVIRCO data. Moreover, the QBO role in producing the Gnevyshev Gap is discussed. A significant correlation has also been found between QBOs of the heliomagnetic field and cosmic ray intensity only during even solar activity cycles, with possible implications for cosmic ray modulation.