Galactic cosmic ray modulation during the last five solar cycles

Abstract

Neutron monitor counts observed at Climax have been used to study galactic cosmic ray modulation during the time interval 1953–2001. This interval covers five solar cycles including four‐field reversal. Cosmic ray intensity (CRI) is better correlated (r = 0.93) to the solar coronal hole area (CHA) than to solar activity represent by the sunspot number (R). The heliospheric current sheet (HCS) tilt angle, Ψ, tracks CRI very well by several solar rotations a head. CRI is anticorrelated to the magnitude of the interplanetary magnetic field (B) as well as to the product of B and solar wind speed (BV). It lags CHA by 3–6 solar rotaion during A < 0. This is the time needed by solar wind to reach ∼25–50 AU where modulation starts. The values of the cross correlation function between CRI and each of the parameters: CHA, R, and BV are higher for A < 0 than for A > 0. CRI lags B by 4 solar rotations and the product BV by 2 solar rotations during A < 0. The solar wind speed is the most effective parameter responsible for the flat CRI time profile during 1972–1978. Galactic cosmic rays (GCRs) particles react mainly to the heliospheric condition near HCS. They drift more slowly during A < 0 than during A > 0.