09:15 〜 09:30
[PEM16-08] 2022年3月に発生したSEPイベントのBepiColomboおよびSTELEO衛星による観測と数値モデリング
キーワード：太陽高エネルギー粒子、多点衛星観測、輸送方程式
Solar Energetic Particles (SEPs) are high-energy charged particles spanning from a few keV to several GeV, which are generated in association with energetic phenomena on the Sun (flares and CMEs), and then are ejected into interplanetary space. Given that SEPs offer insights into acceleration and transport mechanisms in collisionless plasmas, understanding their origin and dynamics is of great interest to space plasma physics and relevant fields (e.g., high-energy astrophysics and laser plasma physics). Furthermore, accurate prediction of the SEP profile is required for space weather operations, as SEPs exceeding 10 MeV pose primary threats to the space environment, including radio communication failure, malfunction and degradation of equipment onboard aircraft and satellites, and radiation exposure of astronauts during extravehicular activities. This is expected to become more and more important in the future as humanity expands its activity beyond the Earth's magnetosphere.
Unraveling the SEP physics presents a formidable challenge. On the theoretical front, the rigorous description of SEPs requires a first-principle kinetic treatment while the system scale of the Sun-Earth environment is far beyond the magnetohydrodynamic scale. On the observational front, SEPs have been conventionally observed by in-situ measurement of an individual satellite, resulting in information about physical mechanisms of acceleration and transport of SEPs being convolved during their journey from the Sun to the observation point. Presently, many satellites are operating to measure SEPs at different radii and longitudes, giving a valuable opportunity to integrate theoretical modeling with multi-satellite observations to extract their physical knowledge.
M and X-class flares, along with subsequent CMEs, occurred on 28 and 30 March, 2022. The propagations of CMEs and background solar wind were reconstructed by the global MHD simulation of the heliosphere based on the ground-based interplanetary scintillation (IPS) observation, IPS-SUSANOO. Two associated SEP events were observed simultaneously by BepiColombo at 0.6 AU and STEREO A at 1 AU. Fortunately, both satellites were positioned approximately along the same Parker spiral. In both events, the Solar Particle Monitor onboard BepiColombo/MMO detected 40-200 MeV ions approximately within one hour after the flare, with their peak exhibiting velocity dispersion indicative of ballistic motion. Time-of-flight analysis suggests the expected starting point to be 0.5-0.7 AU from the BepiColombo, close to the Sun. This is corroborated by the same analysis of 1.8-10 MeV ions detected by the Low Energy Telescope (LET) onboard STEREO A. The BepiColombo Environment Radiation Monitor (BERM) detected 1.5 MeV ions, providing a comparative study with 1.8 MeV ions detected by LET. While the difference in their peak times suggests ballistic motion along the magnetic field, the decay profile observed by LET is more prolonged than that observed by BERM. This observation may imply an increase in scattering over time, potentially indicating a reduction in mean free path to below 0.4 AU, as inferred from focused transport simulations. In this paper, we will present detailed observations and numerical modelling results, and discuss potential scenarios for the transport of SEPs between BepiColombo and STEREO locations.
Unraveling the SEP physics presents a formidable challenge. On the theoretical front, the rigorous description of SEPs requires a first-principle kinetic treatment while the system scale of the Sun-Earth environment is far beyond the magnetohydrodynamic scale. On the observational front, SEPs have been conventionally observed by in-situ measurement of an individual satellite, resulting in information about physical mechanisms of acceleration and transport of SEPs being convolved during their journey from the Sun to the observation point. Presently, many satellites are operating to measure SEPs at different radii and longitudes, giving a valuable opportunity to integrate theoretical modeling with multi-satellite observations to extract their physical knowledge.
M and X-class flares, along with subsequent CMEs, occurred on 28 and 30 March, 2022. The propagations of CMEs and background solar wind were reconstructed by the global MHD simulation of the heliosphere based on the ground-based interplanetary scintillation (IPS) observation, IPS-SUSANOO. Two associated SEP events were observed simultaneously by BepiColombo at 0.6 AU and STEREO A at 1 AU. Fortunately, both satellites were positioned approximately along the same Parker spiral. In both events, the Solar Particle Monitor onboard BepiColombo/MMO detected 40-200 MeV ions approximately within one hour after the flare, with their peak exhibiting velocity dispersion indicative of ballistic motion. Time-of-flight analysis suggests the expected starting point to be 0.5-0.7 AU from the BepiColombo, close to the Sun. This is corroborated by the same analysis of 1.8-10 MeV ions detected by the Low Energy Telescope (LET) onboard STEREO A. The BepiColombo Environment Radiation Monitor (BERM) detected 1.5 MeV ions, providing a comparative study with 1.8 MeV ions detected by LET. While the difference in their peak times suggests ballistic motion along the magnetic field, the decay profile observed by LET is more prolonged than that observed by BERM. This observation may imply an increase in scattering over time, potentially indicating a reduction in mean free path to below 0.4 AU, as inferred from focused transport simulations. In this paper, we will present detailed observations and numerical modelling results, and discuss potential scenarios for the transport of SEPs between BepiColombo and STEREO locations.