Collaborative Research: Transport Processes Affecting High-Energy Solar Energetic Particles Observed at Earth

太阳偶尔会有大规模的喷发，能够产生非常高能的粒子辐射。这些“太阳宇宙射线”在太阳附近产生，穿过太阳和地球之间的空间，并撞击地球的高层大气。这些粒子对太空中的人类和太空硬件构成严重的辐射危害，甚至可能增加航空机组人员接受的辐射剂量。项目团队可以使用地球上的探测器来测量这些粒子，这种探测器被称为中子监测器，它也被用来测量来自太阳系外的银河宇宙射线。将任何给定太阳风暴的大小——即释放的能量或它的大小等——与地球上的粒子强度联系起来，需要对这些粒子如何在太阳和地球之间移动进行仔细而彻底的研究。这种“传输”并不是均匀的，在地球上产生的强度取决于许多因素，比如太空磁场的性质，这些因素必须仔细研究。这就是这个为期三年的合作项目的内容，它包括数值模拟，并将这些模拟结果与中子监测数据进行比较。这些研究解决了了解空间辐射环境和空间天气的一般问题，特别是来自太阳耀斑的辐射环境和空间天气，从而更准确地预测未来。这个为期三年的合作项目将以俯角散射、跨场扩散、场线弯曲和漂移的形式，研究高能太阳粒子的行星际传输在影响地球上观测到的强度和方向方面的作用，这被视为地球中子监测器的地面增强（GLE）。从观测到的强度与时间和各向异性的关系来看，GLE事件常常表现出非常不寻常的特征。有些表现出突然的、短暂的峰值，然后是逐渐衰减，甚至是再次增强，然后是衰减。观测到的剖面提供了关于从太阳到地球的粒子传输性质的重要信息，这一点还没有得到充分的探索。项目小组将进行大量的数值模拟，以解决在一组运动学指定的行星际磁场中移动的大量单个粒子的运动方程。同时，他们还将分析GLE事件的中子监测数据集，描述各个站点的强度与时间的关系。通过合作，他们将确定事件并直接与数值模拟进行比较。数值模拟将考虑一些尚未完全探索的重要新效应，包括可能对~ gev能量粒子产生深远影响的日球层电流片。此外，研究人员将考虑场线弯曲的重要性，这可能导致在地球上看到的高能太阳粒子强度不均匀。该项目的研究和EPO议程支持AGS部门在发现、学习、多样性和跨学科研究方面的战略目标。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Sun occasionally has massive eruptions that are capable of producing very high-energy particulate radiation. These "solar cosmic rays" are created near the Sun, move through space between the Sun and Earth, and impinge on the Earth's upper atmosphere. These particles pose a significant radiation hazard to humans in space, space hardware, and may even increase the radiation dosage received by airline crews. The project teams can measure these particles using Earth-based detectors, known as neutron monitors, which are also used to measure galactic cosmic rays that come from outside our solar system. Relating the size of any given solar storm -- i.e. the amount of energy released or how big it is, etc. -- to the intensity of the particles at Earth requires a careful and thorough study of how these particles move between the Sun and the Earth. This "transport" is not uniform, and the resulting intensity at Earth depends on a number of factors, such as the nature of the magnetic field in space, that must be studied carefully. That is what this three-year collaborative project is about, and it involves numerical modeling and comparing those modeling results with neutron monitor data. The research studies address the general problem of understanding the space radiation environment and space weather especially that from solar flares, leading to more accurate future predictions.This three-year collaborative project will investigate the role of interplanetary transport, in the form of pitch-angle scattering, cross-field diffusion, field-line meandering, and drifts, of high-energy solar particles in affecting the observed intensity and direction at Earth, seen as ground-level enhancements (GLE) in Earth's neutron monitors. GLE events can often show very unusual profiles in terms of the observed intensity versus time and anisotropy. Some show an abrupt, short-lived peak followed by a gradual decay, or even re-enhancement, followed by a decay. The observed profiles provide important information about the nature of the particle transport from the Sun to the Earth, which has not been fully explored. The project teams will perform a large number of numerical simulations which solve the equations of motion of a large number of individual particles moving in a set of kinematically specified interplanetary magnetic fields. In parallel, they will also analyze the neutron monitor data set for GLE events, characterizing the intensity versus time at various stations. Through collaboration, they will identify events to compare directly with the numerical simulations. The numerical simulations will consider a number of important new effects which have not yet been completely explored, including the heliospheric current sheet, which likely has a profound effect on ~GeV-energy particles. In addition, the researchers will consider the importance of field-line meandering, which can lead to a non-uniform intensity of high-energy solar particles seen at Earth. The research and EPO agenda of this project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.