Short-Term Variations of Cosmic-Ray Intensity During the Recent Deep Solar Minimum and the Previous Four Solar Minima: A Wavelet Analysis

Abstract

The recent, unusual solar cycle and solar minima between Cycles 23 and 24 have been studied extensively. Wavelet analysis of hourly cosmic-ray intensity during the last five solar minima reveals a number of short-term variations with few temporal shifts in the periods. This study suggests that deviations with a one-solar-rotation period and its harmonics are small during the recent minimum. However, deviations are considerably larger during the other minima. Analysis also demonstrates that the behavior of active regions is nearly the same during the minima of Cycles 19, 20, 21, and 22. The results also suggest that regions outside the streamer stalk are significantly larger in the recent solar minimum as opposed to the other minima.