Study of high and low amplitude wave trains of cosmic ray diurnal variation during solar cycle 23

Abstract

A detailed study has been conducted on the long-term changes in the diurnal variation of cosmic rays in terms of high and low amplitude wave trains event (HAEs/LAEs) during the period 1996-2008 (solar cycle 23), using the neutron monitor data from Kiel neutron monitoring station. As such, 17 HAE and 48 LAE cases have been detected and analyzed. These HAEs appear quite dominantly during the declining phase as well as near the maximum of the solar activity cycle 23. In contrast, the low amplitude events (LAEs) are inversely correlated with solar activity cycle. In fact, LAEs appear quite dominantly during the minimum phase of the solar activity. When we compare our results for diurnal phase with that observed on an annual average basis, we notice no significant diurnal phase shift for HAEs as well as for LAEs. Moreover, we find that the high-speed solar wind streams (HSSWS) do not play any significant role in causing these variations. These results are discussed on the basis of that observed in earlier cycles.Key words. Cosmic rays-diurnal variation-high amplitude anisotropic events-low amplitude anisotropic events-solar cycle-solar wind speed.

Diurnal Variation of Cosmic Ray Intensity at Different Group of Geomagnetic Index (Ap)

“…The long term vector addition diagram of annual average vectors of first harmonic of diurnal variation it is clearly notice that the annual average diurnal phase is shifting to before hours during the nearly solar activity minima in all the even solar cycles (cycles 20,22). It is observed to move in later hours during the odd solar cycles (21, 23).…”

“…Observed diurnal anisotropy is related to sunspot cycle, which also shown rigidity dependent. Moreover, the amplitude and phase of the diurnal anisotropy changes with period of one or two solar cycles [11][12], [14][15][16][17][18][19][20][21][22]. The time of the maximum diurnal variation shows remarkable and systematic phase shift towards earlier hours compare than normal.…”

Corotating Solar Wind Structures and Recurrent Trains of Enhanced Diurnal Variation in Galactic Cosmic Rays

“…The authors attributed this to convective removal of cosmic rays produced by the higher-speed solar wind streams associated with the larger CH. Singh et al (2010) reported that HSSs did not play any significant role in causing high-and lowamplitude wave train events and the phase did not shift to earlier hours, but the DA decreased during the solar activity minima in 2008. Variations in GCR intensity and anisotropy have also been analyzed in terms of a 27 day periodicity, which provides a statistical description of the effects of HSSs and CIRs.…”