Closed to Open: Particle Signatures Across a Topological Transition

封闭到开放：拓扑转变中的粒子特征

• 批准号: 0548678
• 负责人: Patrick Newell
• 金额: --
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-02-01 至 2010-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0548678&HistoricalAwards=false
• 关键词: Closed; Open; Particle; Signatures; Across

The nature of particle precipitation on closed and open magnetic field lines is quite different, but the transition that the precipitation undergoes when a magnetic field line is first converted from a closed field line to an open one is not well understood. There are several important stages as particle precipitation changes character across the open/closed magnetic field boundary (OCB) which need to be documented, investigated, and understood, because the specifics of these changes have important geophysical consequences. This project will develop a detailed chronology of the transition of particle characteristics across the OCB, based on phenomena such as the low-energy ion cutoff, and basic calculations of electron and ion bounce times. The result of all this will be to provide a toolkit for placing particle observations near the OCB in context. Among the detailed aspects of the transition that will be studied is the drop-out in high-energy magnetospheric ions. Loss at the magnetopause with partial reflection would lead to the highest energy ions disappearing first, while resupply from closed field lines would lead to the highest energy ions lasting longest. The relative importance of these two processes is not yet known. Other issues involve the high-energy magnetospheric electrons, which may more closely follow the convection reversal boundary rather than the OCB. Whether the energetic electrons are energy dispersed across the OCB, and whether the energetic electrons can co-exist with magnetosheath electrons for a time inconsistent with flux tube emptying is not yet known. Other little discussed effects involve the appearance of a "shadow" electron precipitation equatorward of the main cusp (before ions arrive). This population resembles the polar rain or "strahl" electrons. The size of this shadow region varies from virtually non-existent to more than 1 degree, for reasons unknown. All these changes in particle characteristics across the OCB seem to have systematic norms and variants, which may provide important clues for quantitative modeling. The results will also be of use in investigating the extent to which the low latitude boundary layer is open or closed. This project will also continue to maintain a Defense Meteorological Satellite Program (DMSP) resource, distributing particle data through the World Wide Web. The web site (http://sd-www.jhuapl.edu/Aurora) provides researchers around the world with a valuable tool. Because of the ease of access and aids provided at the web site, graduate students and postdoctoral fellows have been heavy users of the system.

在封闭和开放磁力线上粒子沉淀的性质有很大的不同，但是当磁力线从封闭转为开放时，沉淀所经历的转变还不是很清楚。随着粒子降水在开/闭磁场边界（OCB）上的变化特征，有几个重要的阶段需要记录、调查和理解，因为这些变化的细节具有重要的地球物理后果。该项目将基于诸如低能离子切断等现象，以及电子和离子弹跳时间的基本计算，开发出粒子特征在OCB上转变的详细年表。所有这一切的结果将是提供一个工具包，用于在背景中放置靠近OCB的粒子观测。将研究的转变的详细方面之一是高能磁层离子的退出。磁层顶部分反射的损耗会导致能量最高的离子首先消失，而闭合磁场线的再补给会导致能量最高的离子持续时间最长。这两个过程的相对重要性尚不清楚。其他问题涉及高能磁层电子，它们可能更接近于对流逆转边界，而不是OCB。高能电子是否是分散在OCB上的能量，以及高能电子是否能与磁鞘电子共存一段与磁管排空不一致的时间，目前尚不清楚。其他很少讨论的效应包括在主尖端（离子到达之前）赤道方向出现的“影子”电子沉淀。这种电子群类似于极雨或“斯特劳”电子。这个阴影区域的大小从几乎不存在到超过1度不等，原因不明。所有这些粒子特征的变化似乎都有系统的规范和变异，这可能为定量建模提供重要线索。这些结果也将用于研究低纬度边界层的开放或封闭程度。该项目还将继续维护国防气象卫星计划（DMSP）资源，通过万维网分发粒子数据。该网站（http://sd-www.jhuapl.edu/Aurora）为世界各地的研究人员提供了一个有价值的工具。由于易于访问和网站提供的辅助，研究生和博士后一直是该系统的主要用户。