The Origin of Plasmaspheric Hiss

等离子体层嘶嘶声是一种非相干的、频带受限的发射，主要发现于地球周围的高密度等离子体区域，也就是众所周知的等离子体层。HISS在哨声模式下以电磁等离子体波的形式传播，并能够与范艾伦辐射带中的高能电子共振。HISS在控制辐射带的结构和动力学方面的重要性早已得到证实，但HISS本身的起源40多年来一直是一个悬而未决的问题。这个项目将开发一种新发现的涉及合唱波的机制，似乎能够自然地解释观察到的频带、不连贯的性质、昼夜不对称以及对地磁活动的依赖。现有的数值射线跟踪程序将被用于计算波的传播，以及使用由联合释放和辐射效应卫星(CRRES)测量的通量来计算朗道衰减。通过适当地加权合唱波的功率分布，并使用光线跟踪跟踪合唱到嘶嘶的演变，嘶嘶声的强度、频带和波法向角的分布将被量化为离地球的距离、当地时间和纬度的函数。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(A)全球闪电活动、(B)方位向传播的影响和(C)等离子体层羽流中的传播对HISS的贡献。计算的HISS分布将与卫星测量的观测值进行比较。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空间天气很重要。

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.