Theoretical and Experimental Studies of the Rigidity Spectrum of the 27-Day Variation of the Galactic Cosmic Ray Intensity in Different Epochs of Solar Activity

A Gil,M V Alania

doi:10.1007/s11207-012-0204-5

Abstract

We consider the recent, very exceptional, 11-year cycle (2003 – 2009) of solar activity and confirm that the relative amplitude in rigidity spectrum, δD(R)/D(R), which can be approximated by a power law in rigidity R, of the first three harmonics of the 27-day variation of the galactic cosmic ray (GCR) intensity is hard in the maximum and soft in the minimum epochs of solar activity, as was found by neutron monitor data for the period of 1965 – 2002. This property is seen not only in separate minimum and maximum epochs but in individual intervals of a solar Carrington rotation as well: There exist many individual intervals of solar rotation when the expected rigidity spectrum of the 27-day variation of the GCR intensity indeed is hard in the maximum epoch of solar activity and is soft in the minimum epoch. We then construct a three-dimensional model of the 27-day variation of the GCR intensity based on Parker’s transport equation, by implementing in situ measurements of the changes in heliographic longitude of the solar wind velocity and interplanetary magnetic field for different epochs of solar activity.

Highlights

In previous papers (Gil and Alania, 2010, 2011) we have shown that the relative amplitude in rigidity spectrum, δD(R)/D(R), of the first, second, and third harmonics of the 27-day variation of the galactic cosmic ray (GCR) intensity (R is rigidity and δD(R)/D(R) ∝ R−γ )
It is of interest to study whether a similar behavior of the relative amplitude in the rigidity spectrum of the 27-day variation of the GCR intensity takes place in the period of 2003 – 2009, which includes the recent, very extraordinary minimum epoch of solar activity (SA) (e.g. Smith, 2011; Leske et al, 2011; Gil, Modzelewska, and Alania, 2012)
We propose a model of the 27-day variation of the GCR intensity based on Parker’s (1965) transport equation:

Summary

Introduction

In previous papers (Gil and Alania, 2010, 2011) we have shown that the relative amplitude in rigidity spectrum, δD(R)/D(R), of the first, second, and third harmonics of the 27-day variation of the galactic cosmic ray (GCR) intensity (R is rigidity and δD(R)/D(R) ∝ R−γ ). It is of interest to study whether a similar behavior of the relative amplitude in the rigidity spectrum of the 27-day variation of the GCR intensity takes place in the period of 2003 – 2009, which includes the recent, very extraordinary minimum epoch of SA I) We wish to study changes of the exponent γ of the power-law of the rigidity spectrum, δD(R)/D(R), of the first three harmonics of the 27-day variation of the GCR intensity in the period of the recent outstanding 11-year cycle of SA (2003 – 2009), and some individual intervals of a Carrington rotation during maximum, intermediate, and minimum epochs of SA. Ii) We want to construct a three-dimensional (3-D) theoretical model of the 27-day variation of the GCR intensity by implementing in situ measurements of the (heliographic) longitudinal changes of the solar wind velocity and interplanetary magnetic field (IMF) for maximum, intermediate, and minimum epochs of SA

Experimental Data

23 October – 18 November 1991 10 July – 5 August 1994 11 July – 6 August 1997

In the minimum epoch of SA

Conclusions