Hysteresis of Cosmic Rays with Respect to Sunspot Numbers During the Recent Sunspot Minimum

Abstract

Cosmic ray neutron monitors show intensity changes (counts) anti-correlated with sunspot number R _z, but with a lag of a few months. The lag is ∼ 3 months for even cycles and ∼ 9 – 15 months for odd cycles. Thus, for the recently started even Cycle 24, a lag of ∼ 3 months was expected. However, for Cycle 24, whereas R _z had a minimum value (zero) in August 2009, cosmic ray intensity decreased only after March 2010, with a lag of seven months with respect to R _z. Thus, Cycle 24 did not conform to the known pattern of even cycles (lag of ∼ 3 months). It may be noted that the minimum at the juncture of Cycle 23-24 was abnormally long, tens of months instead of few months as in earlier cycles. Also, in this solar minimum, the cosmic ray intensity was much higher than in previous cycles.