Broadband Electron Acceleration: Outstanding Physics Questions

该项目的动机是最近认识到，经过近30年的研究支持极光粒子沉淀是由加速电子的过程主导的，这些电子在单一能量下达到峰值，这一理论可能需要修改。宽带电子加速被认为与色散的阿尔芬波有关，现在被认为具有大致类似的意义，至少在某些时候是这样。为了研究这一想法，将探索由DMSP卫星获得的最大极光降水数据集。识别算法和模式识别技术将被开发并用于对宽带和单能加速的相对出现进行广泛的统计研究。扩散电子和扩散离子沉淀也将包括在研究中。将讨论几个具有重要物理后果的问题，涉及宽带和单能加速之间的关系。这些包括：(1)确定宽带加速是否像单能极光那样受到紫外线照射的影响；(2)与宽带加速有关的加速能量和能量通量是什么？这些数字估计分别为每平方厘米每秒几十keV和几个ergs；(3)极帽弧线包含宽带加速吗？(4)宽带加速是否发生在较低纬度，还是像坊间报道所说的那样罕见。选择这些特定的主题是为了提供对加速机制进行比较的最清晰的物理见解。例如，宽带加速主要发生在椭圆形的极地部分。这可能是因为与高度拉伸的磁力线的关系，或者因为椭圆形向极边缘(如边界层)特有的过程。这项研究提供的答案将有助于理论家建立极光加速的统一模型，并确定哪个过程可能是活跃的。这项工作还将有助于确定漫射电子、漫射离子、单能加速电子和宽带加速电子沉淀的相对比例。该项目的更广泛影响包括根据DMSP卫星的观测结果继续开发和维护一个广泛的极光粒子数据库。Http://sd-www.jhuapl.edu/Aurora，的数据库可以通过网络免费获得，包括各种数据产品，从原始数据到光谱图，再到各种高级数据抽象。该数据库是在早些时候的一笔赠款下开始的，已被空间科学界广泛使用，包括研究生和博士后研究员，但也提供了面向普通公众的信息和文章。

This project is motivated by the recent realization that, after nearly three decades of research supporting the idea that auroral particle precipitation is dominated by processes that accelerate electrons and these electrons peak at a single energy, this theory may require revision. Broadband electron acceleration, which is believed to be associated with dispersive Alfven waves, is now recognized to be of roughly comparable significance, at least at some times. To investigate this idea, the largest data set of auroral precipitation, obtained by the DMSP satellite, will be explored. Identification algorithms and pattern recognition technique will be developed and employed to conduct a broad statistical study of the relative occurrences of broadband versus monoenergetic acceleration. Diffuse electron and diffuse ion precipitation will also be included in the study. Several issues with important physical consequences involving the relationship between broadband and monoenergetic acceleration will be addressed. These include: (1) a determination of whether broadband acceleration is affected by UV insolation, as is true for monoenergetic aurora; (2) what are the acceleration energies and energy fluxes associated with broadband acceleration? The numbers have been estimated to be tens of keV and several ergs per square centimeter per second, respectively; (3) do polar cap arcs contain broadband acceleration? (4) does broadband acceleration occur at lower latitudes, or is it as rare as anecdotal reports suggest. These specific topics are chosen to provide the clearest physical insights into comparing the acceleration mechanisms. For example, broadband acceleration occurs mainly in the poleward portion of the oval. This may occur because of a relationship to highly stretched magnetic field lines, or because of processes particular to the poleward edge of the oval (such as the boundary layer). The answers provided by this study will aid theorists in constructing unified models of auroral acceleration and in deciding when which process is likely to be active. This work will also help establish the relative proportions of diffuse electron, diffuse ion, monoenergetic accelerated electron, and broadband accelerated electron precipitation. The broader impacts of the project include the continuing development and maintenance of an extensive auroral particle database based on the observations from the DMSP satellite. The database, at http://sd-www.jhuapl.edu/Aurora, is freely available via the web and includes a variety of data products, from raw data to spectrograms to various high-level data abstractions. The database was begun under an earlier grant and has been used extensively by the space science community, including graduate students and postdoctoral fellows, but also provides information and articles geared to the general public.