Collaborative Research: SHINE: What is Causing the Deficit of High-Energy Solar Particles in Cycle 24?

合作研究：SHINE：是什么导致第 24 周期高能太阳能粒子的不足？

• 批准号: 1622391
• 负责人: Gang Li
• 金额: $ 15.6万
• 依托单位: University of Alabama in Huntsville
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-15 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1622391&HistoricalAwards=false
• 关键词: Collaborative; Research; SHINE; What; Causing

This 3-year collaborative SHINE project is aimed at exploring and modeling a key under-appreciated aspect of the shock acceleration mechanism of solar energetic particles (SEPs) in the heliosphere, namely the role of the proton seed population in initiating and amplifying the shock acceleration process. This is one of the most important mechanisms in solar and heliospheric physics. The project will also explore how the maximum energy of SEPs can be limited by pre-existing suprathermal seed-particle densities and by the strength and turbulence level of the interplanetary magnetic field, which has been gradually declining over the past several solar cycles. Knowledge of suprathermal seed particle densities can aid in forecasting the maximum intensity of SEP events and in forecasting all-clear periods, providing a valuable space-weather tool. The PATH acceleration and transport model to be employed during this project will be put online, where it can be used by students and researchers to model SEP spectra, time profiles, maximum energies, and composition. This research project is especially relevant to the Solar Probe Plus and Solar Orbiter missions. The project will also employ a student and involve an under-represented minority. This 3-year SHINE project aims to understand the behavior of our Sun, which has dramatically changed in the last decade. The solar wind ram pressure and the solar magnetic field strength fell to a historic low. While solar cycles 22 and 23 were active with large SEP events, solar cycle 24 brought significantly fewer large events. The difference is particularly striking at the high-energy part (tens of MeV/n and up). This change, which has far reaching implications, puzzles the scientific community. This SHINE project aims at identifying the cause of this deficit. The project teams suggest that the two main causes are the reduced IMF strength and associated turbulence level, and reduced density of suprathermal seed particles. They will use the PATH model to understand how the maximum particle energy depends on: (i) the seed population; (ii) the background magnetic field; (iii) the upstream turbulence level; and, (iv) the shock speed and compression ratio. The investigators will also look at how changes in the seed population from solar cycle 23 to solar cycle 24 affect the accelerated spectra. The project is directly relevant to the NSF's SHINE program, because it will provide important knowledge about the acceleration and transport of SEPs during solar eruptive events. Such knowledge is critical for accurate modeling and prediction of space weather conditions from the solar surface to the Earth and beyond. The research and EPO agenda of this project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research.

这个为期 3 年的合作 SHINE 项目旨在探索和模拟日光层中太阳高能粒子 (SEP) 激波加速机制中一个未被充分认识的关键方面，即质子种子群在启动和放大激波加速过程中的作用。 这是太阳和日光层物理学中最重要的机制之一。 该项目还将探索如何通过预先存在的超热种子粒子密度以及行星际磁场的强度和湍流水平来限制SEP的最大能量，在过去的几个太阳周期中，行星际磁场一直在逐渐下降。 了解超热种子粒子密度有助于预测 SEP 事件的最大强度和晴朗时期，从而提供有价值的空间天气工具。 该项目中使用的 PATH 加速和输运模型将上线，学生和研究人员可以使用它来模拟 SEP 谱、时间分布、最大能量和成分。 该研究项目与 Solar Probe Plus 和 Solar Orbiter 任务特别相关。 该项目还将雇用一名学生并涉及代表性不足的少数群体。 这个为期 3 年的 SHINE 项目旨在了解太阳的行为，太阳在过去十年中发生了巨大的变化。 太阳风撞击压力和太阳磁场强度降至历史最低点。 虽然太阳周期 22 和 23 活跃并伴有大型 SEP 事件，但太阳周期 24 带来的大型事件明显较少。 这种差异在高能部分（数十 MeV/n 及以上）尤其显着。 这一变化具有深远的影响，令科学界感到困惑。 该 SHINE 项目旨在找出造成这种赤字的原因。 项目团队认为，两个主要原因是 IMF 强度和相关湍流水平降低，以及超热种子颗粒密度降低。 他们将使用 PATH 模型来了解最大粒子能量如何取决于：(i) 种子种群； (ii) 背景磁场； (iii) 上游湍流水平； (iv) 冲击速度和压缩比。 研究人员还将研究太阳周期 23 到太阳周期 24 期间种子种群的变化如何影响加速光谱。 该项目与 NSF 的 SHINE 计划直接相关，因为它将提供有关太阳喷发事件期间 SEP 加速和传输的重要知识。 这些知识对于准确建模和预测从太阳表面到地球及其他地方的空间天气状况至关重要。 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。