Study of intensive solar flares in the rise phase of solar cycle 23 and 24 and other activities

Abstract

We present a statistical study and comparison on the properties of intensive solar flares (>M5.0 X-ray flare), decameter–hectometric (DH) wavelength [frequency, 1–14 MHz] type II radio bursts and solar energetic particle (SEP) events during the rising phase of solar cycles 23 and 24. The period of study is May 1996–November 2000 for solar cycle 23 and December 2008–June 2013 for solar cycle 24. Apart from reported weakness of solar cycle 24 compared to the cycle 23, we noted the following differences between the two cycles on the properties of these activities associated with intensive flares: (i) The reduction in the number of intensive flares (>M5.0 class) in cycle 24 is ∼34 %, similar to the reduction in sunspot number reported by Gopalswamy et al. (2014a); (ii) The slightly higher mean starting-frequency (4.15 MHz) and lower ending frequency (0.58 MHz) in cycle 24 compared to those of cycle 23 (2.63 and 0.89 MHz, respectively) indicate that the radio emission of this cycle started closer to the Sun and the CME-shock travelled farther away from the Sun in cycle 24; (iv) Cycle 23 produced a nearly equal number of SEP events as cycle 24 during the rising phase. The correlation between SEP intensity and CME speed is more prominent in cycle 23 ($\mbox{CC}=0.7$) than in cycle 24 ($\mbox{CC}=0.3$).