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

这一为期3年的合作项目旨在探索和模拟日光层中太阳高能粒子(SEPs)激波加速机制中一个被低估的关键方面，即质子种子群在启动和放大激波加速过程中的作用。这是太阳和日球层物理学中最重要的机制之一。该项目还将探索SEP的最大能量如何受到先前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的限制，在过去的几个太阳周期中，星际磁场一直在逐渐下降。关于过热种子颗粒密度的知识可以帮助预测SEP事件的最大强度和预报晴朗时期，提供了一个宝贵的空间气象工具。将在本项目中使用的路径加速和传输模型将上线，学生和研究人员可以使用它来模拟SEP频谱、时间分布、最大能量和成分。这项研究项目与太阳探测器和太阳轨道器任务特别相关。该项目还将雇用一名学生，并涉及代表人数不足的少数族裔。这个为期3年的阳光项目旨在了解太阳的行为，在过去的十年里，太阳的行为发生了戏剧性的变化。太阳风冲击压力和太阳磁场强度降至历史最低点。太阳周期22和23活跃着大型SEP事件，而太阳周期24带来的大型事件明显较少。这种差异在高能部分(几十兆电子伏安及以上)尤为显著。这一变化具有深远的影响，令科学界感到困惑。这项SHARE项目旨在找出造成这种赤字的原因。项目组认为，两个主要原因是IMF强度和相关湍流水平降低，以及过热种子颗粒密度降低。他们将使用路径模型来理解最大粒子能量如何依赖于：(I)种子种群；(Ii)背景磁场；(Iii)上游湍流水平；以及(Iv)激波速度和压缩比。研究人员还将研究种子种群从第23太阳周期到第24太阳周期的变化如何影响加速光谱。该项目与NSF的SIRE计划直接相关，因为它将提供有关太阳喷发事件期间SEP加速和运输的重要知识。这些知识对于准确模拟和预测从太阳表面到地球乃至更远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。

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.