Comparative Study of First Two Harmonics in Cosmic Ray Intensity for the Period 1964-95


Abstract: The Deep River neutron monitor data has been harmonically analyzed for the period 1964--95 covering three solar cycles 20, 21 and 22, looking for a long term trend of the diurnal and semi-diurnal anisotropies of cosmic ray intensity on geomagnetically 60 quiet days. The amplitude of both the harmonics remains statistically constant during 1964-70. The amplitudes of the first harmonic is found to be low during 1965, 1967, 1976-77, 1986-87, 1991, 1993 and 1995. The amplitude of diurnal anisotropy acquired exceptionally large values in 1985, whereas semi-diurnal anisotropy acquired large values in 1974-75 and in 1984, which coincided with epochs of high-speed solar wind stream (HSSWS). The phase of the diurnal anisotropy has shifted to earlier hours in 1976 and 1995, whereas the phase of semi-diurnal anisotropy has significantly shifted to earlier hours during 1967, 1977, 1991 and 1995, periods of close to minimum solar activity. The diurnal phase shows a shift to later hours during 1971, 1985, 1987 and 1991, whereas semidiurnal phase shows a shift to later hours during 1980, 1984 and 1989.

Keywords: Cosmic rays, Diurnal, Semi-diurnal, Anisotropy and Solar poloidal magnetic field.

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