Energy Spectrum of the Recurrent Variation of Galactic Cosmic Rays During the Solar Minimum of Cycles 23/24

Abstract

The Sun during the recent epoch of solar activity operated in a different way than during the last 60 years, being less active. We study temporal changes of the energy spectrum of the first three harmonics of the 27-day variation of the galactic cosmic rays (GCR) intensity during the unusual, recent solar minimum, between Solar Cycles 23 and 24 (SC 23/24) and compare with four previous minima. We show that the energy spectrum of the amplitudes of the recurrent variation of the GCR intensity is hard in the maximum epochs and is soft in the minimum epochs during Solar Cycles 20 -24, but with peculiarities during the Solar Minimum 23/24. In particular, while the energy/rigidity spectrum of the amplitudes of the first harmonic of the recurrent variation of the GCR intensity behaves practically the same as for previous epochs, the energy/rigidity spectrum of the amplitudes of the second and the third harmonics demonstrates a pronounced softening. We attribute this phenomenon to the decrease of the extension of the heliosphere caused by the decrease of the solar-wind dynamic pressure during the unusual Solar Minimum 23/24.

Study of the 27-day variations of GCR in 2007-2008 based on PAMELA and ARINA observations

“…The rigidity dependence of A27 was predominantly investigated on the base of NMs, i.e. at R above several GV, where a power-law behavior was found with an index from 0.4 to 1.4 [9] which is consistent with our results. A clear maximum around R ~1 GV was initially observed in 1992-1994 during the out-of-ecliptic journey of the Ulysses spacecraft [22].…”

“…This paper is devoted to the well-known episode of the 27-day GCR variation in 2007-2008, near the minimum of solar cycle 23, the period exclusively favorable for the development of the pronounced and long-lived recurrent GCR variation. This episode was extensively studied based on the observations with the neutron monitors (NMs) [e.g., [8][9][10] and the space probes [e.g., [11][12][13]. All authors stressed very stable period ~ 27 days and a strong negative correlation of the 27-day waves in GCR and solar wind velocity.…”

Modulation effect of magnetic corotating trap on 27-day cosmic ray variation in November–December 2014

“…Распространение КЛ в гелиосфере при наличии таких неоднородностей вызывает 27-дневную вариацию. Исследованию влияния коротирующих структур СВ на поведение КЛ посвящены многочисленные работы, например [Lee et al, 2010;Modzelewska, Alania, 2013;Gil, Alania, 2016].…”

Modulation effect of magnetic corotating trap on 27-day cosmic ray variation in November–December 2014

“…CR propagation in the heliosphere in the presence of such inhomogeneities causes a 27-day variation. The influence of corotating SW structures on CR behavior has been extensively studied [Lee et al, 2010;Modzelewska, Alania, 2013;Gil, Alania, 2016].…”