日球鞘内能量氢原子和源质子的能谱的时空特征

The energetic ions in the heliosheath can charge exchange with cold hydrogen atoms in the Local Interstellar wind and then become energetic neutral atoms (ENAs). These ENAs will carry the information of their parent ions and leave the heliosheath along a ballistic trajectory. The studies of these ENAs and their parent ions in the heliosheath can greatly help in understanding the energy transport and particle acceleration in the outer boundary of the heliosphere, and thus its dynamics. The important questions that need to be addressed in the study of the heliosheath particles are: how does the energy transport in the heliosheath vary with time and space and what are the causes? Where and how are pickup ions (that are closely related to the energy transport in the heliosheath) accelerated in the heliosheath? Where and how are Anomalous Cosmic Rays (ACRs) (that are believed to originate from the accelerated pickup ions) accelerated in the heliosheath? First, We propose to construct the first temporal and spatial distributions of the energy spectrum of ENAs and their parent ions in the heliosheath, using the ENA measurements from STEREO,IBEX and Cassini, and to investigate the causes that lead to such distributions. Secondly, we will compare observations with the past models of the heliosheath particle acceleration, and examine the actual acceleration location and mechanisms of pickup ions in the heliosheath. Finally, we will compare the spectrum of energized pickup ions and its variation in the heliosheath with the measurements of Anomalous Cosmic Rays, and investigate the acceleration location and mechanisms of ACRs in the heliosheath.

日鞘内的高能质子可以和星际介质风中的冷氢原子发生电荷交换转变成为能量氢原子。这些能量氢原子携带着源质子的信息，沿着直线从日鞘向外运动。因此，对日鞘内的能量氢原子和源质子的研究会有力地促进对日球层边界区中的能量转换和粒子加速过程的认识，从而推动日球层边界区动力学的研究。目前，日鞘内粒子研究中尚需解决的重要问题是：日鞘内能量转化的时空特征及其成因是未知的；与能量转化紧密相关的中等能量离子的加速区和机制是不清楚的；起源于这些离子的异常宇宙射线的加速区和机制也是不清楚的。本项目将利用STEREO、IBEX和Cassini飞船的观测，首次建立日球鞘内能量氢原子和源质子从低能到高能的能谱的时空特征的描述，揭示其形成的原因和机制；检验以往的日球层边界区粒子加速理论，探索日鞘内中等能量粒子的加速区和机制；分析日鞘内质子能谱和其时空变化特征与异常宇宙射线的观测的相关性，探索异常宇宙射线的加速区和机制。

在本基金面上项目《日球鞘内能量氢原子和源质子的能谱的时空特征－项目批准号：41274172》 的支持下，我们完成了几个方面的研究工作。我们研究了日球层内太阳风高能粒子的时空特征，完善了对能量中性氢原子观测的噪声分析。我们发现平静时期太阳风高能电子具有接近各向同性的角分布和幂律能谱，提出这些高能粒子可能源自太阳风源区的加速过程或行星际中波粒相互作用的加速过程。我们建立了一个2.5维的MHD数值模型，模拟太阳风源区的粒子加速过程，研究结果表明此过程是行星际中高能粒子的一个重要来源。我们还完善了从能量氢原子的观测数据重构其源离子信息的数值模型，研究了激波对质子的加速和相应的能量氢原子的转化生成过程，模拟结果与能量氢原子的卫星观测结果相符，在此基础上进一步提出了对能量氢原子的卫星观测设计的改善方案。