Abstract
Galactic Cosmic Rays (GCRs) entering the heliosphere are subject to modulation processes due to variable solar magnetic activity. Finding a relationship between cosmic-ray variations and the heliospheric parameters is important for reconstruction of solar activity in the past. Here, we develop a semi-empirical model describing the heliospheric modulation of GCRs in terms of heliospheric parameters such as the open solar magnetic flux, the tilt angle of the heliospheric current sheet and the polarity of the large scale solar magnetic field. Our model is fitted using annual data obtained for the period 1976–2013, which includes the very weak solar minimum during 2008–2010. The model shows a good agreement with the data, and therefore, can be used for reconstructions of the modulation potential at different levels of solar activity. The model’s validity is also tested using the cosmogenic radionuclides 14 C and 10 Be stored in terrestrial archives. The tilt angle used to fit the parameters in our semi-empirical modulation model is reconstructed by a mathematical model described here.
Highlights
A theory describing Galactic Cosmic Rays (GCRs) transport in the heliosphere (Parker 1965; Krymskij 1969) includes four main processes: diffusion of particles along and perpendicular to the heliospheric magnetic field (HMF), outward convection and adiabatic deceleration in the expanding solar wind (SW), gradient and curvature drifts in the large scale HMF and drift due to the tilted heliospheric current sheet (HCS)
We develop a semi-empirical model describing the heliospheric modulation of GCRs in terms of heliospheric parameters such as the open solar magnetic flux, the tilt angle of the heliospheric current sheet and the polarity of the large scale solar magnetic field
By applying our model, the modulation potential since 1616, a parameter that describes the mean energy loss of GCR particles within the heliosphere due to solar modulation, and using that, we model the global production of radionuclides 14C and 10Be, adopting the method described in Kovaltsov et al (2012) and Kovaltsov & Usoskin (2010), respectively
Summary
A theory describing Galactic Cosmic Rays (GCRs) transport in the heliosphere (Parker 1965; Krymskij 1969) includes four main processes: diffusion of particles along and perpendicular to the heliospheric magnetic field (HMF), outward convection and adiabatic deceleration in the expanding solar wind (SW), gradient and curvature drifts in the large scale HMF and drift due to the tilted heliospheric current sheet (HCS). This interplay results in spatial and temporal variations of GCRs intensity and energy. The modelled series are compared with the records from terrestrial archives such as tree rings (Roth & Joos 2013) and ice cores (Berggren et al 2009)
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