The Origin of Plasmaspheric Hiss

等离子层嘶嘶声的起源

• 批准号: 0840178
• 负责人: Jacob Bortnik
• 金额: $ 33.99万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0840178&HistoricalAwards=false
• 关键词: Origin; Plasmaspheric; Hiss

Plasmaspheric hiss is an incoherent, band-limited emission found predominantly in the dense-plasma region surrounding the Earth, known as the plasmasphere. Hiss propagates as an electromagnetic plasma wave in the whistler mode, and is able to resonate with the high-energy electrons in the Van Allen radiation belts. The importance of hiss in controlling the structure and dynamics of the radiation belts has long been established, but the origin of hiss itself has been an open problem for over four decades. This project will develop a newly discovered mechanism involving chorus waves that appears to be able to naturally account for the observed frequency band, the incoherent nature, the day/night asymmetry, and the dependence on geomagnetic activity. An existing numerical ray tracing code will be used to calculate wave propagation, together with Landau damping using fluxes measured by the Combined Release and Radiation Effects Satellite (CRRES). By properly weighting the power distribution of chorus waves and tracking the evolution of chorus into hiss using ray tracing, the distribution of hiss intensity, frequency band, and wave normal angle will be quantified as a function of distance from the Earth, magnetic local time, and latitude. The effects of geomagnetic activity on the distribution of hiss characteristics will then be analyzed by recalculating the ray database under a number of different magnetospheric conditions. In the final year of the study, the project will determine contribution to hiss from (a) global lightning activity, (b) the effects of azimuthal propagation, and (c) propagation in plasmaspheric plumes. The computed hiss distributions will be compared with observations from satellite measurements. The research will be done primarily by a young research scientist and a postdoctoral scholar. Understanding the physics of the radiation belts is important to understanding and being able to forecast space weather.

等离子体的嘶嘶声是一种非相干的、带限制的发射，主要存在于地球周围的致密等离子体区域，即等离子体层。在哨声模式下，嘶嘶声以电磁等离子体波的形式传播，并且能够与范艾伦辐射带中的高能电子产生共振。在控制辐射带的结构和动力学方面，嘶嘶声的重要性早已确立，但嘶嘶声本身的起源在四十多年来一直是一个悬而未决的问题。该项目将开发一种涉及合唱波的新发现机制，这种机制似乎能够自然地解释观测到的频带、非相干性、昼夜不对称性以及对地磁活动的依赖。现有的数值射线追踪代码将用于计算波的传播，以及使用释放和辐射效应联合卫星（CRRES）测量的通量计算朗道阻尼。通过适当地加权合唱波的功率分布，并使用射线追踪跟踪合唱波向嘶嘶的演变，可以将嘶嘶强度、频带和波法向角的分布量化为与地球的距离、磁地方时和纬度的函数。然后，将通过重新计算若干不同磁层条件下的射线数据库来分析地磁活动对hiss特征分布的影响。在研究的最后一年，该项目将确定以下因素对嘶嘶的贡献：(a)全球闪电活动，(b)方位传播的影响，以及(c)等离子体羽流的传播。计算得到的噪声分布将与卫星观测结果进行比较。这项研究将主要由一名年轻的研究科学家和一名博士后学者完成。了解辐射带的物理特性对于理解和预测太空天气非常重要。