Investigation of diurnal and seasonal galactic cosmic ray variations on quiet days in two mid latitude stations

Abstract

Data from the cosmic ray neutron monitors at Climax (39.4°N, 253.8°E) and Rome (41.9°N, 12.5°E) have been analyzed by Fourier method to obtain the first four harmonics of its variation. Multivariate correlation analysis was performed on the harmonics to remove the contributions of the heliospheric and geomagnetic modulations. The seasonal and yearly averages of diurnal variations were plotted for the two stations on solar cycle basis. The Rome stations diurnal variation showed a peak at about 12:00–14:00 local meridian time (LMT) during the solar maximum period. The diurnal variation during solar minimum leads that of the maximum with as much as 2–4 h. We report for the first time (from available literature) a pre-noon peak in the diurnal variation at about 8:00 LMT at the Rome station during solar minimum. This observation has consistently been smoothed out in previous and recent studies. We also established that the pre-noon peak is repeated after 22 years. We found a weak correlation (<0.2) at ( r = 0.95) between the galactic cosmic ray harmonics and geomagnetic/solar heliospheric variations. The seasonal correlation analysis shows that the GCR intensity clearly correlates well with solar activity and heliospheric modulation. There appears to be a seasonal trend in the GCR flux correlation with sunspot number ( R) where the correlation is greatest in the June solstice and least in the December Solstice suggesting a dependence on the Earths eccentricity. We infer that the phase reversal is controlled by the solar polar magnetic field reversal associated with the 22 year solar activity cycle rather than the 11 year sunspot cycle. These results have significant implications for understanding the anomalies of GCR flux associations with atmospheric and geophysical forcing.