# Modeling Transport of Energetic Particles in Corotating Interaction Region -- A case Study

## TL;DR

This study models energetic particle transport in Corotating Interaction Regions using a case study from 2008, combining observations and Monte Carlo simulations to understand particle modulation and shock acceleration.

## Contribution

It introduces a method to estimate shock locations and particle intensities in CIRs by integrating in-situ data with focused transport simulations assuming no cross-field diffusion.

## Key findings

- Significant modulation of sub-MeV/nucleon particles observed.
- Particle acceleration is more efficient at larger heliocentric distances.
- Monte Carlo simulations match observations when assuming increased particle acceleration farther from the Sun.

## Abstract

We investigate energetic particle transport in Corotating Interaction Regions (CIRs) through a case study. The CIR event we study occurred on $2008$ February $08$ and was observed by both the Advanced Composition Explorer (ACE) and the twin Solar TErrestrial RElations Observatory (STEREO)-B spacecraft. An in-situ reverse shock was observed by STEREO-B ($1.0$ AU) but not ACE ($0.98$ AU). Using STEREO-B observations and assuming the CIR structure does not vary significantly in the corotating frame, we estimate the shock location at later times for both the STEREO-B and ACE observations. Further assuming the accelerated particle spectral shape at the shock does not vary with shock location, we calculate the particle differential intensities as observed by ACE and STEREO-B at two different times by solving the focused transport equation using a Monte-Carlo simulation. We assume that particles move along Parker's field and experience no cross-field diffusion. We find that the modulation of sub-MeV/nucleon particles is significant. To obtain reasonable comparisons between the simulations and the observations by both ACE and STEREO-B, one has to assume that the CIR shock can accelerate more particles at a larger heliocentric distance than at a smaller heliocentric distance.