On the 27-day Variations of Cosmic Ray Intensity in Recent Solar Minimum 23/24

TL;DR

This study analyzes 27-day variations in cosmic ray intensity, solar wind, and magnetic fields during solar minimum 23/24, revealing their stability, relation to solar rotation, and implications for heliospheric structure and solar cycle onset.

Contribution

It provides new insights into the global 3-D nature of GCR variations and the influence of solar differential rotation during a prolonged solar minimum.

Findings

27-day variations are stable and linked to solar rotation.

GCR intensity periods increased to 33-36 days in 2009.

Higher latitude active regions influence GCR variation periods.

Abstract

We have studied the 27-day variations and their harmonics of the galactic cosmic ray (GCR) intensity, solar wind velocity, and interplanetary magnetic field (IMF) components in the recent prolonged solar minimum 23 24. The time evolution of the quasi-periodicity in these parameters connected with the Suns rotation reveals that their synodic period is stable and is aprox 26-27 days. This means that the changes in the solar wind speed and IMF are related to the Suns near equatorial regions in considering the differential rotation of the Sun. However, the solar wind parameters observed near the Earths orbit provide only the conditions in the limited local vicinity of the equatorial region in the heliosphere (within in latitude). We also demonstrate that the observed period of the GCR intensity connected with the Suns rotation increased up to aprox 33-36 days in 2009. This means that the process driving the 27-day variations of the GCR intensity takes place not only in the limited local surroundings of the equatorial region but in the global 3-D space of the heliosphere, covering also higher latitude regions. A relatively long period ( aprox 34 days) found for 2009 in the GCR intensity gives possible evidence of the onset of cycle 24 due to active regions at higher latitudes and rotating slowly because of the Suns differential rotation. We also discuss the effect of differential rotation on the theoretical model of the 27-day variations of the GCR intensity.