The First Ground‐Level Enhancement of Solar Cycle 25 as Seen by the High‐Energy Particle Detector (HEPD‐01) on Board the CSES‐01 Satellite

Abstract

In this work we present the High‐Energy Particle Detector (HEPD‐01) observations of proton fluxes from space during the 28 October 2021 solar energetic particle event, which produced a ground‐level enhancement on Earth. The event was associated with the major, long‐duration X1‐class flare and the concomitant coronal mass ejection (CME) that erupted from the Active Region 12887. This is the first direct measurement from space of solar particles emitted during the current solar cycle, recorded by a single instrument in the energy range from ∼50 MeV/n up to ∼250 MeV/n. We have performed a Weibull‐modeled spectral analysis of the energy spectrum in the wide energy range 300 keV–250 MeV, obtained from combination of HEPD‐01 proton measurements with the ones from ACE/ULEIS, SOHO/EPHIN, and SOHO/ERNE. The good agreement between data and model, also corroborated by a comparison with other spectral shapes commonly used in these studies, suggests that particles could have possibly been accelerated out from the ambient corona through the contribution of stochastic acceleration at the CME‐driven shock, even if the presence of seed populations influencing spectral shape could not be excluded. Finally, a Solar Proton Release time of 16:01 UTC ± 13 min and a magnetic path‐length of L = 1.32 ± 0.24 AU have been obtained, in agreement with previous results for this event. We remark that new and precise data on protons in the tens/hundreds MeV energy range—like the one provided by HEPD‐01—could shed more light on particle acceleration as well as provide a reliable parametrization of solar energetic particle spectra for Space Weather purposes.

Time Dependence of 50–250 MeV Galactic Cosmic-Ray Protons between Solar Cycles 24 and 25, Measured by the High-energy Particle Detector on board the CSES-01 Satellite

“…We used a single map for the entire period 2018-2022, after checking the stability (on average) of the geomagnetic environment over a year-by-year basis. Indeed, it turned out that, only during major solar events-like the one observed by HEPD-01 in Martucci et al (2023), the disturbance of the magnetic field of the Earth was high enough to affect ∼50-60 MeV proton populations. However, these periods were excluded from the analysis, as mentioned before.…”

Particle monitoring capability of the Solar Orbiter Metis coronagraph through the increasing phase of solar cycle 25

“…A more recent event characterized by particle acceleration above 2 GeV was observed on October 28, 2021 by several instruments in space, including EPD/HET aboard Solar Orbiter, and with neutron monitors (NMs) on Earth. During this event, Solar Orbiter was almost radially aligned with Earth (see for details Papaioannou et al 2022;Martucci et al 2023). The solar eruption started with an X1.0 class flare at 15:17 UT and peaked at 15:35 UT.…”

What Is the Radiation Impact of Extreme Solar Energetic Particle Events on Mars?

“…(2018, Table 2) calibrated spectral parameters for 59 GLE events together with the ESP components of 6 events (GLE42, GLE43, GLE58, GLE59, GLE62, and GLE65) occurring in 1956–2012. In addition, we also include the spectra of the most recent two events: GLE72 (Bruno et al., 2019) and GLE73 (Guo et al., 2023; Martucci et al., 2023). All of the GLE event spectra used in this article are shown in Figure 1.…”