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 (Astroparticle Physics 07/2011; 34(12):878-885. DOI:10.1016/j.astropartphys.2011.03.002
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