Long‐Term Monitoring of Energetic Protons at the Bottom of Earth’s Radiation Belt
Abstract The energetic particles in the Earth's radiation belt are known to fluctuate over various timescales. Although observations using satellites have been made for more than 50 years, there are few examples of continuous and long‐term observations at low altitude (<2,000 km) and in low...
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| Format: | Article |
| Language: | English |
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Wiley
2021-01-01
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| Series: | Space Weather |
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| Online Access: | https://doi.org/10.1029/2020SW002611 |
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| author | K. Yoshioka Y. Miyoshi S. Kurita M. Teramoto F. Tsuchiya A. Yamazaki G. Murakami T. Kimura H. Kita I. Yoshikawa Y. Kasaba |
| author_facet | K. Yoshioka Y. Miyoshi S. Kurita M. Teramoto F. Tsuchiya A. Yamazaki G. Murakami T. Kimura H. Kita I. Yoshikawa Y. Kasaba |
| author_sort | K. Yoshioka |
| collection | DOAJ |
| description | Abstract The energetic particles in the Earth's radiation belt are known to fluctuate over various timescales. Although observations using satellites have been made for more than 50 years, there are few examples of continuous and long‐term observations at low altitude (<2,000 km) and in low L‐value (L < 2) regions, which are at the bottom of the inner radiation belt. This is because the orbits of satellites that are designed to cover large areas of the magnetosphere are not suitable for long‐term continuous observations at low altitudes. In this study, we focused on data from a space telescope that usually follows a low‐altitude circular orbit. The Hisaki space telescope, launched in 2013, continuously observes the planets from an altitude of ∼1,000 km (L‐value 1–2). By using the noise component counted on the photodetector of Hisaki as a radiation monitor, the flux variation of the high‐energy protons (energy > 30 MeV) in this orbit can be observed. The results show a clear dependence on solar activity. At around L = 2, it is found that the variation in the radiation belt proton flux is controlled by both the flux of the galactic cosmic rays and the neutral density of the thermosphere. The former one is the source process of high‐energy charged particles in the inner radiation belt, and the latter is the loss process due to the Coulomb collision. It is also found that the influence of galactic cosmic ray fluctuations becomes smaller as the L‐value moves closer to 1. |
| format | Article |
| id | doaj-art-e37b4291d88e4051b37d6d07b61d88bd |
| institution | Kabale University |
| issn | 1542-7390 |
| language | English |
| publishDate | 2021-01-01 |
| publisher | Wiley |
| record_format | Article |
| series | Space Weather |
| spelling | doaj-art-e37b4291d88e4051b37d6d07b61d88bd2025-01-14T16:27:00ZengWileySpace Weather1542-73902021-01-01191n/an/a10.1029/2020SW002611Long‐Term Monitoring of Energetic Protons at the Bottom of Earth’s Radiation BeltK. Yoshioka0Y. Miyoshi1S. Kurita2M. Teramoto3F. Tsuchiya4A. Yamazaki5G. Murakami6T. Kimura7H. Kita8I. Yoshikawa9Y. Kasaba10Graduate School of Frontier Sciences The University of Tokyo Kashiwa JapanInstitute for Space‐Earth Environmental Research Nagoya University Naogya JapanResearch Institute for Sustainable Humanosphere Kyoto University Uji JapanGraduate School of Engineering Kyusyu Institute of Technology Kita‐kyushu JapanGraduate School of Science Tohoku University Sendai JapanInstitute of Space and Astronautical Science Sagamihara JapanInstitute of Space and Astronautical Science Sagamihara JapanThe Frontier Research Institute for Interdisciplinary Sciences Tohoku University Sendai JapanGraduate School of Engineering Tohoku Institute of Technology Sendai JapanGraduate School of Frontier Sciences The University of Tokyo Kashiwa JapanGraduate School of Science Tohoku University Sendai JapanAbstract The energetic particles in the Earth's radiation belt are known to fluctuate over various timescales. Although observations using satellites have been made for more than 50 years, there are few examples of continuous and long‐term observations at low altitude (<2,000 km) and in low L‐value (L < 2) regions, which are at the bottom of the inner radiation belt. This is because the orbits of satellites that are designed to cover large areas of the magnetosphere are not suitable for long‐term continuous observations at low altitudes. In this study, we focused on data from a space telescope that usually follows a low‐altitude circular orbit. The Hisaki space telescope, launched in 2013, continuously observes the planets from an altitude of ∼1,000 km (L‐value 1–2). By using the noise component counted on the photodetector of Hisaki as a radiation monitor, the flux variation of the high‐energy protons (energy > 30 MeV) in this orbit can be observed. The results show a clear dependence on solar activity. At around L = 2, it is found that the variation in the radiation belt proton flux is controlled by both the flux of the galactic cosmic rays and the neutral density of the thermosphere. The former one is the source process of high‐energy charged particles in the inner radiation belt, and the latter is the loss process due to the Coulomb collision. It is also found that the influence of galactic cosmic ray fluctuations becomes smaller as the L‐value moves closer to 1.https://doi.org/10.1029/2020SW002611annual variationEarth's radiation beltspace telescope |
| spellingShingle | K. Yoshioka Y. Miyoshi S. Kurita M. Teramoto F. Tsuchiya A. Yamazaki G. Murakami T. Kimura H. Kita I. Yoshikawa Y. Kasaba Long‐Term Monitoring of Energetic Protons at the Bottom of Earth’s Radiation Belt Space Weather annual variation Earth's radiation belt space telescope |
| title | Long‐Term Monitoring of Energetic Protons at the Bottom of Earth’s Radiation Belt |
| title_full | Long‐Term Monitoring of Energetic Protons at the Bottom of Earth’s Radiation Belt |
| title_fullStr | Long‐Term Monitoring of Energetic Protons at the Bottom of Earth’s Radiation Belt |
| title_full_unstemmed | Long‐Term Monitoring of Energetic Protons at the Bottom of Earth’s Radiation Belt |
| title_short | Long‐Term Monitoring of Energetic Protons at the Bottom of Earth’s Radiation Belt |
| title_sort | long term monitoring of energetic protons at the bottom of earth s radiation belt |
| topic | annual variation Earth's radiation belt space telescope |
| url | https://doi.org/10.1029/2020SW002611 |
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