The East-West Asymmetry of Particle Intensity in Energetic Storm Particle Events

TL;DR

This study uses an advanced model to analyze the east-west asymmetry in energetic storm particle events, revealing that injection efficiency and ion properties significantly influence peak intensities and their asymmetries.

Contribution

The paper introduces the use of the improved iPATH model to explain the east-west asymmetry in ESP peak intensities, emphasizing injection efficiency and ion charge-to-mass ratio effects.

Findings

Eastern flank peaks are generally higher in intensity.

Injection efficiency correlates with peak intensity asymmetry.

Heavy ion asymmetry depends on ion energy and charge-to-mass ratio.

Abstract

We examine the East-West asymmetry of the peak intensity in energetic storm particle (ESP) events using the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model. We find that injection efficiency peaks east of the nose of coronal mass ejection shock where the shock exhibits a quasi-parallel geometry. We show that the peak intensity at the eastern flank is generally larger than that at the western flank and it positively correlates with the injection efficiency. We also examine this asymmetry for heavy ions, which depends sensitively on the ion energy. Comparison between the modelling results with the measurements of ESP events at 1 au shows a reasonable agreement. We suggest that the injection efficiency can be a primary factor leading to the East-West asymmetry of the peak intensity in ESP events. Additionally, the charge-to-mass (Q/A) dependence of the maximum particle energy affects this asymmetry for heavy ions.