Letter to the Editor

The heliomagnetic and solar-cycle related variations of the cosmic ray flux modeled with the BoPo-hybrid code

¹ Institut für Astrophysik und Extraterrestrische Forschung, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: kls@tp4.rub.de
² Now at: Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
³ Unit for Space Physics, School of Physics, North-West University, 2520 Potchefstroom, South Africa e-mail: fsksesf@puknet.puk.ac.za

Received: 27 June 2005
Accepted: 3 September 2005

Abstract

Based on the five species hybrid model by Scherer & Ferreira (2005, ASTRA, 1, 17) we describe the observations of energetic cosmic ray particles by the Voyager 1 spacecraft for solar minimum and maximum conditions during both the as well the heliomagnetic cycle. Without going into a detailed data and model analysis, we will show that the model (BoPo-code) is well suited to explain the longterm trend in the observed proton data as this spacecraft moves into the outer heliosphere. By comparison of model results to the observations along the Voyager trajectory we predict, depending on cosmic ray energy, a smooth transition in observed radial profiles after the crossing of the termination shock. From a cosmic ray particle perspective the effect of the shock might be seen in the very low energy data (<30 MeV), where a change in radial gradient occurs over the shock. Also, as Voyager 1 moves into the heliosheath, we show that the solar-cycle related changes in cosmic ray observations, which are clearly observed inside the termination shock, are expected to decrease toward the heliopause beyond which the LISM spectra is assumed to be unperturbed.