Analysis of the Longitudinal Spread of Impulsive SEP Events Uisng Time-Intensity Profiles and Energetic Ion Spectra
Date
2024-07-02
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Abstract
Impulsive solar energetic particle (SEP) events occur when protons, electrons, and heavier nuclei are accelerated to high energies (hundreds of MeV) in solar flares and are then observed in interplanetary space. Impulsive SEP events typically last a few minutes to a few hours and have heightened 3He/4He and Fe/O ratios compared to solar wind abundances1. Typically, these events have a longitudinal spread of 20°-40°. However, for unknown reasons, some impulsive events have been observed to have a wide ( 130°) longitudinal spread. Understanding why some impulsive SEP events are not constrained to a small longitudinal spread or perhaps undergo cross-field diffusion helps us increase our understanding of energetic particle transport and the interplanetary magnetic field configuration.
In this study time-intensity profiles and energetic ion spectra for Helium (Helium-3 and Helium-4 when available), Carbon, Oxygen, and Iron in energy ranges from a few keV to 70 MeV are used to examine the longitudinal spread of six SEP events. These events are April 2-3, 2019, April 4, 2019, April 20-23, 2019, July 11, 2020, July 20, 2020, and May 24-25, 2021, which were previously identified in Mitchell et al. (2023) or Mason et al. (2020). The analysis used four different spacecraft: Parker Solar Probe/IS⊙IS/EPI-Lo, ACE/ULEIS, STEREO-A/IMPACT/LET, and Solar Orbiter/EPD/SIS. We use the findings to discuss the longitudinal spread of heavy ion spectra which show a wide range of longitudinal spreads from event to event.
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Physics, Astronomy, Solar Physics