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

太阳偶尔会发生大规模喷发，能够产生非常高能量的粒子辐射。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，撞击地球的上层大气。这些粒子对太空中的人类构成了重大的辐射危险，空间硬件，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，也被用来测量来自太阳系以外的星系宇宙射线。将任何给定太阳风暴的大小--即释放的能量或其大小等--与地球上粒子的强度联系起来，需要仔细和彻底地研究这些粒子如何在太阳和地球之间移动。这种“传输”并不是统一的，在地球上产生的强度取决于许多因素，例如太空中磁场的性质，必须仔细研究。这就是这个为期三年的合作项目的意义所在，它涉及到数值建模，并将建模结果与中子监测数据进行比较。这项研究致力于了解空间辐射环境和空间天气，特别是太阳耀斑的辐射环境和空间天气，从而产生更准确的未来预测。这项为期三年的合作项目将调查高能太阳粒子的俯仰角散射、跨场扩散、场线漂移和漂移形式的星际运输在影响地球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)。根据观测到的强度与时间和各向异性的关系，GLE事件通常会显示出非常不寻常的轮廓。有些显示出突然的、短暂的峰值，然后是逐渐衰减，甚至是再次增强，然后是衰变。观测到的轮廓提供了有关粒子从太阳到地球运输性质的重要信息，这一点还没有得到充分的探索。项目团队将进行大量的数值模拟，以解决大量单个粒子在一组以运动学方式指定的行星际磁场中运动的运动方程。同时，他们还将分析GLE事件的中子监测数据集，表征不同站点的强度与时间的关系。通过合作，他们将确定要直接与数值模拟进行比较的事件。数值模拟将考虑一些尚未完全探索的重要新效应，包括日球层电流片，它可能对~GeV-能量粒子有深远的影响。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的强度不均匀。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NSF的法定使命，并通过使用基金会的智力优势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.