Cosmic ray modulation at neutron monitor energies

1Mishra, RA, 2Mishra, RK
1Department of Physics, Govt. Model Science College (Autonomous), Jabalpur (M. P.) 482 001, India
2Computer and IT Section, Tropical Forest Research Institute, P. O. RFRC, Mandla Road, Jabalpur (M. P.) 482 021, India
Kosm. nauka tehnol. 2008, 14 ;(3):019-028
Publication Language: English
The present work deals with the study of the first three harmonics of cosmic ray intensity on geo-magnetically quiet days from 1981 to 1993 for the Deep River and Inuvik neutron monitoring stations having mid and low cutoff rigidity. The amplitude of the first harmonic remains high for Deep River having mid cutoff rigidity as compared to the Inuvik neutron monitor having low cutoff rigidity on quiet days. The diurnal amplitude significantly decreases and phase shifts towards an earlier time during solar activity minimum years at both Deep River and Inuvik. The amplitude of the second harmonic significantly enhanced during solar activity minimum as well as maximum at Deep River and remains low during solar activity maximum at Inuvik, whereas the phase shifts towards an earlier time during solar maximum for both the stations. The amplitude of the third harmonic significantly enhanced during solar activity minimum at Deep River and during solar activity minimum at Inuvik, whereas the phase does not show any significant characteristics and fluctuates quite frequently. The amplitude of semi/tri-diurnal anisotropy has a good positive correlation, while the others (i.e., amplitude and phase) have a very weak correlation with solar wind velocity on quiet days at the Deep River station during 1981 ‒1993.
             The solar wind velocity significantly remains in the range from 350 to 425 km/s, i.e., it is nearly average on quiet days. The amplitude and direction of the anisotropy on quiet days depend only weakly on high-speed solar wind streams for the two neutron monitoring stations of mid and low cutoff rigidity threshold. The amplitude as well as direction of the second harmonic has a good anti-correlation with interplanetary magnetic field Bz  and the product Vx´Bz on quiet days at the Deep River station. The direction of the second and third harmonics has a good anti-correlation with interplanetary magnetic field Bz and the product Vx´Bz on quiet days at Inuvik station.
Keywords: amplitude, cosmic ray, harmonic, neutron monitor
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