Research Article

An empirical model of heliospheric cosmic ray modulation on long-term time scale

¹ ReSoLVE Centre of Excellence, University of Oulu, 90014 Oulu, Finland
² Sodankylä Geophysical Observatory, University of Oulu, Oulu, FIN-90014, Finland

^* Corresponding author: Eleanna.Asvestari@oulu.fi

Received: 5 November 2015
Accepted: 5 February 2016

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 ¹⁴C and ¹⁰Be 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.