Latitudinal Dependence of Cosmic Rays Modulation at 1 AU and Interplanetary-Magnetic-Field Polar Correction

TL;DR

This study models how the structure of the interplanetary magnetic field, including polar corrections, influences cosmic ray intensity and latitudinal gradients at 1 AU, improving understanding of solar modulation effects.

Contribution

It introduces a polar-corrected IMF model within the HelMod Monte Carlo code to better simulate cosmic ray modulation and latitudinal gradients at 1 AU.

Findings

Polar correction affects proton intensity distribution.

Latitudinal gradients are sensitive to IMF modifications.

Model aligns with Ulysses spacecraft observations.

Abstract

The cosmic rays differential intensity inside the heliosphere, for energy below 30 GeV/nuc, depends on solar activity and interplanetary magnetic field polarity. This variation, termed solar modulation, is described using a 2-D (radius and colatitude) Monte Carlo approach for solving the Parker transport equation that includes diffusion, convection, magnetic drift and adiabatic energy loss. Since the whole transport is strongly related to the interplanetary magnetic field (IMF) structure, a better understanding of his description is needed in order to reproduce the cosmic rays intensity at the Earth, as well as outside the ecliptic plane. In this work an interplanetary magnetic field model including the standard description on ecliptic region and a polar correction is presented. This treatment of the IMF, implemented in the HelMod Monte Carlo code (version 2.0), was used to determine the effects on the differential intensity of Proton at 1\,AU and allowed one to investigate how latitudinal gradients of proton intensities, observed in the inner heliosphere with the Ulysses spacecraft during 1995, can be affected by the modification of the IMF in the polar regions.