Local Times of Galactic Cosmic Ray Intensity Maximum and Minimum in the Diurnal Variation

• Main Authors: Su Yeon Oh, Yu Yi
• Format: Article
• Language: English
• Published: Korean Space Science Society (KSSS) 2006-06-01
• Series: Journal of Astronomy and Space Sciences
• Subjects: galactic cosmic rays; diurnal variation; solar maximum & minimum
• Online Access: http://ocean.kisti.re.kr/downfile/volume/kosss/OJOOBS/2006/v23n2/OJOOBS_2006_v23n2_117.pdf
• ISSN: 2093-5587; 2093-1409

The Diurnal variation of galactic cosmic ray (GCR) flux intensity observed by the ground Neutron Monitor (NM) shows a sinusoidal pattern with the amplitude of 1sim 2 % of daily mean. We carried out a statistical study on tendencies of the local times of GCR intensity daily maximum and minimum. To test the influences of the solar activity and the location (cut-off rigidity) on the distribution in the local times of maximum and minimum GCR intensity, we have examined the data of 1996 (solar minimum) and 2000 (solar maximum) at the low-latitude Haleakala (latitude: 20.72 N, cut-off rigidity: 12.91 GeV) and the high-latitude Oulu (latitude: 65.05 N, cut-off rigidity: 0.81 GeV) NM stations. The most frequent local times of the GCR intensity daily maximum and minimum come later about 2sim3 hours in the solar activity maximum year 2000 than in the solar activity minimum year 1996. Oulu NM station whose cut-off rigidity is smaller has the most frequent local times of the GCR intensity maximum and minimum later by 2sim3 hours from those of Haleakala station. This feature is more evident at the solar maximum. The phase of the daily variation in GCR is dependent upon the interplanetary magnetic field varying with the solar activity and the cut-off rigidity varying with the geographic latitude.