Geomagnetic Storm Effects on the LEO Proton Flux During Solar Energetic Particle Events

• Published in: Space Weather Vol. 21; no. 12
• Main Authors: Girgis, Kirolosse M., Hada, Tohru, Yoshikawa, Akimasa, Matsukiyo, Shuichi, Pierrard, Viviane, Samwel, Susan W.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.12.2023; Wiley
• Subjects: Astronauts; DST Index; Earth orbits; Earth surface; Energetic particles; Fluctuations; Geomagnetic field; Geomagnetic storm effects; Geomagnetic storms; Geomagnetism; Inner radiation belt; Latitude; Low earth orbits; Magnetic field configurations; Magnetic fields; Magnetic storms; Mathematical models; Proton flux; Radiation; Radiation belts; Radiation dosage; Relativistic particles; Satellite observation; Satellite technology; Satellites; Single event upsets; Solar energetic particles; Solar energy; Solar magnetic field; Solar particle events; Solar proton flux; Solar protons; Solar storms; Storm effects; Storms; Trajectories
• DOI: 10.1029/2023SW003664
• ISSN: 1542-7390; 1539-4964

During a few solar energetic particle (SEP) events, solar protons were trapped within the geomagnetic field and reached the outer edge of the inner radiation belt. We reproduced this phenomenon by modeling the proton flux distribution at the Low‐Earth Orbit (LEO) for different geomagnetic conditions during solar particle events. We developed a three‐dimensional relativistic test particle simulation code to compute the 70–180 MeV solar proton Lorentz trajectories in low L‐shell range from 1 to 3. The Tsyganenko model (T01) generated the background static magnetic field with the IGRF (v12) model. We have selected three Dst index values: −7, −150, and −210 nT, to define quiet time, strong, and severe geomagnetic storms and to generate the corresponding inner magnetic field configurations. Our results showed that the simulated solar proton flux was more enhanced in the high‐latitude regions and more expanded toward the lower latitude range as long as the geomagnetic storm was intensified. Satellite observations and geomagnetic cutoff rigidities confirmed the numerical results. Furthermore, the LEO proton flux distribution was deformed, so the structure of the proton flux inside the South Atlantic Anomaly (SAA) became longitudinally extended as the Dst index decreased. Moreover, we have assessed the corresponding radiation environment of the LEO mission. We realized that, for a higher inclined LEO mission during an intense geomagnetic storm (Dst = −210 nT), the probability of the occurrence of the Single Event Upset (SEU) rates increased by 19% and the estimated accumulated absorbed radiation doses increased by 17% in comparison with quiet conditions. Plain Language Summary Solar energetic particles are high‐energy particles emitted from the Sun during intense activity. When they reach the Earth, they become trapped in its magnetic field. In some cases, these trapped solar particles can penetrate deeper toward the Earth's surface when some fluctuations in the Earth's magnetic field occur. The impact of solar particles on satellite technologies and astronauts is significant and dangerous. In this work, we reproduced this phenomenon by developing a numerical code to calculate the solar proton trajectories inside the Earth's magnetic field according to several geomagnetic conditions. Our new results successfully produced the same physical process and did agree with other methodologies, such as satellite observations. Afterward, we estimated the resulting radiation environment of a Low‐Earth Orbit mission. We found that a satellite could suffer more radiation risks of around 20% if a Solar Energetic Particle event occurred during an intense geomagnetic storm. Key Points We have numerically modeled the Low‐Earth Orbit proton flux due to precipitated solar protons for different geomagnetic storm conditions Our test particle simulations reproduced the proton flux enhancement at high latitudes, agreeing with observations and cutoff rigidities During a stronger geomagnetic storm and solar energetic particle event, a spacecraft that enters the polar cap region would be subject to more radiation risks