Solar modulations by the regular heliospheric electromagnetic field

TL;DR

This paper proposes a novel approach to modeling cosmic ray solar modulation by focusing solely on the regular heliospheric magnetic field and the resulting large-scale electric field, highlighting deterministic energy losses.

Contribution

It introduces a new model that neglects turbulence, emphasizing the role of the regular magnetic and electric fields in solar modulation of cosmic rays.

Findings

Energy loss depends on particle charge and is largely energy-independent.

The regular electric field causes significant energy losses for particles reaching Earth.

The model suggests a dominant deterministic component in solar modulation effects.

Abstract

The standard way to model the cosmic ray solar modulations is via the Parker equation, that is as the effect of diffusion in the turbulent magnetic of an expanding solar wind. Calculations performed with this method that do not include a description of the regular magnetic field in the heliosphere predict, in disagreement with the observations, equal modulations for particles and antiparticles. The effects of the regular heliospheric field, that break the the particle/anti-particle symmetry, have been included in the Parker equation adding convection terms associated to the magnetic drift velocity of charged particles moving in non--homogeneous magnetic field. In this work we take a completely different approach and study the propagation of charged particles in the heliosphere assuming only the presence of the regular magnetic field, and completely neglecting the random component. Assuming that the field is purely magnetic in the wind frame, one can deduce the existence of a large scale electric field, that results in important energy losses for charged particles that traverse the heliosphere and reach the Earth. The energy loss (Delta E) due to the large scale regular electric field depends on the particle electric charge, is proportional to the absolute value of the electric charge, and to a good approximation is independent from the particle energy and direction. We speculate that this deterministic energy loss is an important, or perhaps even the leading contribution to the solar modulation effects.