On the mechanisms of the quasi-biennial oscillations in the GCR intensity

Abstract

Quasi-biennial oscillation (QBO) is a well-known quasi-periodical variation with characteristic time 0.5-4 years in different solar, heliospheric and cosmic ray characteristics. Recently it has been shown that there are low correlation between the solar and heliospheric QBOs and rather high anticorrelation between the QBOs in galactic cosmic ray (GCR) intensity near the Earth and in the strength of the heliospheric magnetic field (HMF). Besides, it was suggested that both steplike changes of the GCR intensity and Gnevyshev Gap effect (a temporal damping of the solar modulation around the sunspot maxima) could be viewed as the manifestations of QBO. Some suggestions were also made on the mechanisms of QBO in the GCR intensity. In this paper a hypothesis is checked on the causes of the apparent lack of correlation between solar and heliospheric QBOs, then the possible mechanisms of QBO in the GCR intensity are discussed as well as the idea of the same nature of the step-like changes and Gnevyshev Gap effects in the GCR intensity. Our main conclusions are as follows: 1. In thefirst approximation the hypothesis is justified that the change in the sunspot and QBO cycles in the transition from the Sun to the heliosphere is due to 1) the different magnitude and time behavior of the large-scale and small-scale photospheric solar magnetic fields and 2) the stronger attenuation of the small-scale fields in this transition. 2. As the QBO in the HMF strength influences both the diffusion coefficients and drift velocity, it can give rise to the complex QBO in the GCR intensity with respect to the dominating HMF polarity. The description of drift velocity field for the periods of the HMF inversion is suggested, although it has drawbacks. 3. As the conditions in the heliosphere are quite different around the sunspot maximum and during the periods of low solar activity (both with respect to the HMF polarity distribution and with the presence or absence of the large-scale barriers), the suggestion that both the step-like changes of the GCR intensity and Gnevyshev Gap effect could have the same nature, looks questionable.