27-day Variation of the Three Dimensional Solar Anisotropy of Galactic Cosmic Ray: 1965-2014

TL;DR

This study analyzes 50 years of 3D galactic cosmic ray anisotropy, revealing solar cycle influences, polarity dependence, and north-south asymmetry variations linked to solar magnetic activity and interplanetary magnetic fields.

Contribution

It provides a comprehensive analysis of the 27-day variation of 3D GCR anisotropy over five decades, highlighting solar cycle effects and polarity dependence with detailed observational data.

Findings

Amplitude of anisotropy varies with solar polarity.

Clear 11-year solar cycle pattern in anisotropy variations.

North-south asymmetry correlates with solar cycle and IMF components.

Abstract

The temporal evaluation of the 27-day variation of the three dimensional (3D) galactic cosmic ray (GCR) anisotropy has been studied for 1965-2014. 3D anisotropy vector was obtained based on the neutron monitors and Nagoya muon telescopes data. We analyze the 27-day variation of the (1) two dimensional (2D) GCR anisotropy in the ecliptic plane, and (2) north-south anisotropy normal to the ecliptic plane. Studying the time line of the 27-day variation of the 2D GCR anisotropy, we confirm that the average amplitude in the minimum epoch of solar activity is polarity dependent, as it is expected from the drift theory. The amplitude in the negative polarity epochs is less as we had shown before. The feeble 11-year variation connected with solar cycle and strong 22-year pattern connected with solar magnetic cycle is visible in the 27-day variation of the 2D anisotropy for 1965-2014. We show that the 27-day variation of the GG index (being a measure of the north-south asymmetry) varies in accordance to solar cycle with a period of 11-years, being in good agreement with the 27-day variation of the At component of the GCR anisotropy calculated by the IZMIRAN group. Detailed analysis are presented for the solar minimum 2007-2008 of solar cycle no.23 and solar maximum 2013-2015 of solar cycle no 24. In the solar cycle no. 24 GG index, calculated by Nagoya telescopes data, is highly anticorrelated with By component of the interplanetary magnetic field (IMF) and shows a clear recurrent changes related to the Sun's rotation.