Investigating Solar Sources of Helium-Rich and Helium-Poor SEP Events in 2024 using Solar Orbiter

Title: Investigating Solar Sources of  ³He-Rich and  ³He-Poor SEP Events in 2024 using

Solar Orbiter HET

Authors:

Sindhuja. G¹, Robert F. Schweingruber¹, Patrick Kühl¹, Alexander Kollhoff¹, Zheyi Ding¹, Sebastian

Fleth¹, Lars

Berger¹, Javier Rodriguez-Pacheco², George C. Ho³, Glenn M. Mason⁴, Raul Gomez-

Herrero², Francisco Espinosa Lara², Ignacio Cernuda², Stephan Böttcher¹, Sandra Eldrum¹, and

Robert C. Allen³,

1) Institute of Experimental and Applied Physics, Kiel University, Leibnizstaße 11, DE-24118

Kiel.

2) Universidad de Alcalá, Space Research Group, 28805 Alcalá de Henares, Spain

3) Southwest Research Institute, San Antonio, TX, USA

4) Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA

Abstract:

This study focuses on the solar sources of  ³He-rich and ³He-poor solar energetic particle

(SEP) events observed in 2024, utilizing data from the High-Energy Telescope (HET) onboard

the Solar Orbiter mission. The HET instrument, which measures the energy spectra of energetic

particles—including helium and protons—operates in the energy range of ~7–500 MeV/nucleon

and provides critical insights into particle acceleration in the inner heliosphere. The SEP

events were selected based on specific criteria: comparable ³He^/4He ratios in Suprathermal Ion

Spectrograph (SIS) and HET at 8.2 MeV data, a Type III radio burst association with the event,

and an increase in electron flux within the 10-100 MeV energy range. These events include both

³He-rich and  ³He-poor types, providing an opportunity to explore the differences in their

solar origins.

In particular, ³He-rich events are significant as they offer valuable insights into the mechanisms

of particle acceleration and transport associated with coronal mass ejections (CMEs). Our

analysis aims to compare the energy spectra and particle composition between ³He-rich and

³He-poor events, shedding light on the underlying physical processes that govern these

phenomena. By examining the solar sources of these distinct event types, we seek to uncover the

factors contributing to variations in helium content and acceleration mechanisms.

Furthermore, we present the kinematics of associated CMEs and flare properties, offering a comprehensive

view of the dynamics behind these SEP events. This study is expected to enhance our

understanding of the role of helium-rich events in the solar wind and their potential impacts on

Earth's magnetosphere, ultimately contributing to the broader comprehension of heliospheric dynamics

and solar particle acceleration processes.