【直播】【北大空间物理系列讲座】Xinlin Li: Recent Advances in Understanding...
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本次报告由北京大学空间物理与应用技术研究所主办，于2021年10月13日10:00开始，授权蔻享学术进行网络直播。
Recent Advances in Understanding Cosmic Rays and Their Relations to Earth's Radiation Belt, Contributions of Our CubeSat Missions and Future Plans
报告人
Xinlin Li 教授（University of Colorado）
时 间
2021年10月13日 10:00
Soon after the discovery of Earth’s Van Allen radiation belts six decades ago it was recognized that the decay of knock-on neutrons is the main source of trapped energetic (above 10s of MeV) inner belt protons. Only recently has it been recognized, based on our first CubeSat (CSSWE) measurements, [e.g., Li et al., Nature, 2017] that the decay of low energy neutrons contributes to energetic electrons (up to 782 keV) and is the dominant source of energetic electrons at the inner edge of the inner belt. This discovery was confirmed and consolidated by further energy spectrum analysis, theoretical modeling, and a long-term measurements of sub-MeV electrons in the inner belt from other satellites. As for inner belt protons, detailed analysis of Van Allen Probes data showed that the solar proton source dominates at L>1.5 and energies <100 MeV and the CRAND source dominates otherwise. Inward diffusion of 10s of MeV solar protons to L<2 adds to and merges with the pre-existing trapped protons in the inner belt. Long-term measurements of 10s of MeV protons at low-Earth orbit (LEO) show a clear solar cycle variation which anti-correlates with sunspot number. However, the magnitude of the variation is much greater than the solar cycle variation of galactic cosmic rays (>GeV) that are regarded as a source of these trapped protons. With respect to protons (>36 MeV) mirroring near the magnetic equator, both measurements and simulations show no clear solar cycle variation at L>1.2, but there is clear solar cycle variation and a strong spatial proton flux gradient at L≤1.2. A comparison between measurements and simulations shows that energy loss of trapped protons due to collisions with free and bound electrons in the ionosphere and atmosphere is the dominant mechanism for the strong spatial gradient and solar cycle variation at the inner edge of the inner belt protons. This fact is also of key importance for spacecraft and instrument design and operation in near-Earth space. Our next CubeSat, Colorado Inner Radiation Belt Experiment (CIRBE), has just been fully integrated, and will go through Vibration test and Thermo-Vacuum test soon, and will be ready for launch in 2022.
个人简介
Xinlin Li, Professor
Dept. of Aerospace Engineering Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado, 3665 Discovery Drive, Boulder, Colorado 80303; 303-492-3514; lix@lasp.colorado.edu
Employment:
2002-Present, Dept. of Aerospace Engineering Science (AES) and Laboratory for Atmospheric and Space Physics (LASP), University of Colorado (CU) at Boulder, Associate/Full Professor (since 2011)
Education:
Ph.D. Dartmouth College, 1992.
M.S. ShanghaiInstitute of Optics and Fine Mechanics, Academia Sinica, 1985
B.S. University of Science and Technology of China, 1982
Honor: AGU Fellow (class of 2021)
Research Experience:
Principal research interests are studies of solar wind energy coupling into Earth’s magnetosphere and of energetic particle dynamics in the magnetosphere, and of space weather.
He led a group of graduate and undergraduate students (> 65) as they designed, built, calibrated, and tested, with close mentoring from LASP professionals, a NSF-funded CubeSat (Colorado Student Space Weather Experiment, CSSWE), which measured energetic particles in space for more than two years, 2012-2014. There have been 24 peer-reviewed papers and five Ph.D. dissertations associated with this mission, including one published in Nature in December 2017. He was invited to present the results associated with CSSWE at Capitol Hill twice (2018 and 2019) to Senators, Congressional Representatives, their staff members, and leaders from various government agencies (including NASA and NSF) to advocate for more research funding for University Small Satellites/CubeSat programs.
In 2018, he was awarded a NASA CubeSat project: Inner Radiation Belt Experiment (CIRBE), which is currently under development and scheduled to be launched in early 2023, involving a group of graduate and undergraduate students (>15) and professional engineers (~10part time).In 2019, he was awarded a NASA Heliophysics Instrument Development project: Medium Energy Electron Telescope (MEET), to refine the measurements of electrons in the energy range of 30 keV- 400 keV.
Teaching: His teaching activities include aerospace environment, space orbit dynamics, spaceflight hardware design, and thermodynamics and heat transfer.
Publications: authored and co-authored over 210 peer-reviewed publications. Total citations: > 12,000; H-index: 60 (based on Google Scholar in October 2021)
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