Long Term Average Observation of First Two Harmonics of Cosmic Ray Daily Variation

Cosmic ray daily variation is directly related with changes in interplanetary conditions. The significant and systematic deviations in the amplitude and phase of the diurnal, semi-diurnal variation of cosmic rays from the average values is due to strong geomagnetic and solar activity. The amplitudes and phases (time of maxima) of first two harmonics of cosmic ray daily variation show 11/22 years variability. In the present study the observational values of 22 nd and 23 rd cycle for various harmonics, particularly at neutron monitor energies have been used to compare their characteristic values. As the latitude of NM station gets higher, the phase gets delayed, that is, the phase shifted to the later hour. For first harmonic we also observed that for both the stations the time of maxima shifted to earlier hours during solar minima (II-Quadrant) for solar cycle 22 and for solar cycle 23, the time of maxima shifted to later hours. The amplitudes are found to be larger for maxima and for the descending phase of solar cycle for both the stations. The semi-diurnal amplitudes vary from the range of 0.01% to 0.08%. However, the spread of phases is larger, in comparison to diurnal anisotropy. The spread is to be found much larger during the high solar activity period. The time of maxima for KIEL station spreads in I and IV quadrant.