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.

中文翻译：

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长期监测地球辐射带底部的高能质子

已知地球辐射带中的高能粒子会在各种时间范围内波动。尽管使用卫星进行观测已经有50多年的历史了，但很少有在低海拔（<2,000 km）和低L值（L  <2）区域（位于底部）连续和长期观测的例子。内部辐射带。这是因为设计用于覆盖磁层大面积区域的卫星的轨道不适合在低海拔地区进行长期连续观测。在这项研究中，我们集中于通常遵循低空圆形轨道的太空望远镜的数据。于2013年发射的Hisaki太空望远镜连续不断地从约1,000 km（L-值1-2）。通过使用Hisaki光电探测器上计数的噪声分量作为辐射监测器，可以观察到该轨道上高能质子的通量变化（能量> 30 MeV）。结果表明明显依赖于太阳活动。在L  = 2附近，发现辐射带质子通量的变化受银河系宇宙射线通量和热层中性密度的控制。前者是内部辐射带中高能带电粒子的源过程，后者是由于库仑碰撞而造成的损失过程。还发现，随着L值接近1 ，银河宇宙射线波动的影响会变小。