Is the Solar Wind Electron Strahl a Seed Population for the Earth's Electron Radiation Belt?

近地空间充满了来自太阳风和地球上层大气的带电粒子。然而，这些粒子是如何加速并进入辐射带的仍然是个谜。这个磁层项目将探索一条可能的途径，以识别地球电子辐射带的最终源种群，并识别该源种群的控制因素。理由如下。(1)由于电子辐射带有时会丢失，因此需要一个高能电子的种子群来代替电子辐射带。(2)一般认为辐射带种子居群是由亚暴注入到偶极子中的高能电子居群。(3)这些亚暴注入的电子是地球磁尾等离子体片中的超热电子，它们通过亚暴从磁尾绝热地传递到偶极子中。(4)由此产生的问题是：磁尾超热电子从何而来，又是什么因素控制它们？本项目认为，磁尾超热电子来自太阳风中的高能电子流。这个NSF项目的目标是：(1)确定太阳风电子流是否（以及以多少）作为地球电子辐射带的种子种群；(2)确定这一过程的控制因素；(3)追踪太阳风电子流，进入地球磁尾等离子体片，进入亚暴注入，并演变成电子辐射带；(4)判别磁尾等离子体片中是否有其他来源的超热电子变成高能亚暴注入电子。在本项目的多样化数据分析中，将统计跟踪地球太阳风中的strahl电子种群进入磁尾等离子体片，进入亚风暴电子注入，进入电子辐射带。数据分析将由计算机模拟指导，以回答有关strahl电子种群进入并穿过磁层-电离层系统时的演变问题。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 near-Earth space is filled with charged particles from the solar wind and the Earth's upper atmosphere. However, how these particles are accelerated and transported into the radiation belt remains a mystery. This Magnetospheric project will explore a possible pathway to discern the ultimate source population of the Earth's electron radiation belt and discern the controlling factors for that source population. The reasoning is as follows. (1) Because the electron radiation belt is lost on occasion, a seed population of energetic electrons is required to replace the belt. (2) It is commonly accepted that the radiation-belt seed population is the population of energetic electrons injected into the dipole by substorms. (3) These substorm-injected electrons are suprathermal electrons in the Earth's magnetotail plasma sheet that are adiabatically delivered from the magnetotail into the dipole by substorms. (4) A resulting question is: where do the magnetotail suprathermal electrons come from, and what factors control them? This project argues that the magnetotail suprathermal electrons come from the energetic electron strahl in the solar wind.The objectives of this NSF project are: (1) To determine whether (and by how much) the solar-wind electron strahl acts as a seed population for the Earth's electron radiation belt, (2) To determine the controlling factors for this process, (3) To trace the electron strahl from the solar wind, into the Earth's magnetotail plasma sheet, into substorm injections, and evolving into the electron radiation belt, and (4) To discern whether there are other sources of the suprathermal electrons in the magnetotail plasma sheet that become energetic substorm- injected electrons. In the diverse data analysis of this project, the strahl electron population in the solar wind at Earth will be statistically followed into the magnetotail plasma sheet, into substorm electron injections, and into the electron radiation belt. The data analysis will be guided by computer simulations to answer questions about the evolution of the strahl electron population as it enters into and traverses through the magnetosphere-ionosphere system.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.