GEM: Quantifying the Rate of Diffuse Auroral Electron Precipitation

GEM：量化漫射极光电子降水率

• 批准号: 0802843
• 负责人: Richard Thorne
• 金额: $ 40万
• 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: 2008
• 资助国家: 美国
• 起止时间: 2008-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0802843&HistoricalAwards=false
• 关键词: GEM; Quantifying; Rate; Diffuse; Auroral

Diffuse auroral precipitation provides a major source of energy input to the Earth's upper atmosphere. The precipitated particles lead to changes in the rate of ionization, which can modulate large natural current systems and induce electrical currents along transmission lines and pipelines. The additional ionization can also result in chemical changes to the neutral atmosphere, which has been linked with ozone-depletion. The precipitated particles also lead to changes in the electrical conductivity of the ionosphere, which maps along magnetic-field lines and further affect the transport of plasma in the magnetosphere. The diffuse aurora is primarily caused by rapid pitch-angle scattering of plasma sheet electrons. Because the magnetosphere is essentially collisionless, the only viable mechanism that can cause pitch-angle scattering is wave-particle interactions. Previous studies have shown that scattering by both electrostatic electron cyclotron harmonic (ECH) waves and whistler-mode chorus could be important, but there is still no general consensus on the dominant process. This project will examine the roles of ECH and chorus waves by looking at the rate of wave-induced particle scattering by both classes of wave. Pitch-angle diffusion rates will be calculated with existing codes, based on a comprehensive analysis of the spectral properties of chorus and ECH waves observed by the CRRES satellite in the outer magnetosphere, under different levels of magnetic activity. Computed rates of electron scattering will be used to determine the equilibrium pitch-angle distribution and the rate of precipitation loss to the atmosphere compared to the limit imposed by strong diffusion. The scattering results will be used, together with statistical data on the global distribution of trapped electrons in the near-Earth plasma sheet, to model the global distribution of diffuse auroral emissivity. This study will provide a quantitative understanding of how microphysical processes regulate the transfer of energy in geospace. The proposed research is central to the primary science objectives of the new GEM Focus Group on Diffuse Auroral Precipitation. Much of the research will be undertaken by a graduate student and a young research scientist. The scientific results obtained will be made available to other members of the magnetospheric community interested in modeling the global distribution of the ring current electron population and diffuse auroral precipitation under different geomagnetic conditions. The results of the study can be used to model the global distribution of ionospheric conductivity, which regulates the rate of magnetospheric convection, and is critical for the development of a Geospace General Circulation Model. Quantification of electron scattering rates in the near-Earth plasmasheet is also important for understanding the evolution of electron flux and pitch angle distributions during injection events, which provide the source of free energy for the excitation of waves affecting energetic radiation belt dynamics. The important physical processes studied at Earth, can be applied to other magnetized planets such as Jupiter and Saturn, where similar scattering can occur.

漫射极光降水是地球高层大气能量输入的主要来源。沉淀的颗粒导致电离率的变化，这可以调制大的自然电流系统，并沿沿着传输线和管道感应电流。额外的电离也可能导致中性大气的化学变化，这与臭氧消耗有关。沉淀的粒子也会导致电离层电导率的变化，这会沿着沿着磁场线映射，并进一步影响等离子体在磁层中的传输。扩散极光主要是由等离子体片电子的快速俯仰角散射引起的。由于磁层本质上是无碰撞的，唯一可行的机制，可以导致俯仰角散射是波粒相互作用。以前的研究表明，散射的静电电子回旋谐波（ECH）波和哨声模式合唱可能是重要的，但仍然没有普遍的共识，占主导地位的过程。本计画将借由观察两种波所引起的粒子散射率，来探讨ECH波与合唱波的角色。将根据对CRRES卫星在不同磁活动水平下观测到的外磁层合唱波和ECH波的频谱特性的综合分析，利用现有代码计算俯仰角扩散率。计算的电子散射率将用于确定平衡俯仰角分布和大气降水损失率，与强扩散所施加的限制相比。散射结果将与关于近地等离子体片中被捕获电子的全球分布的统计数据一起用于模拟漫射极光发射率的全球分布。这项研究将提供一个定量的了解如何微物理过程调节地球空间的能量转移。拟议的研究是新的全球环境监测系统极光扩散降水重点小组的主要科学目标的核心。大部分研究将由一名研究生和一名年轻的研究科学家进行。所获得的科学成果将提供给磁层界其他有兴趣模拟不同地磁条件下环流电子总数和扩散极光降水全球分布的成员。研究结果可用于模拟电离层电导率的全球分布，这种电导率调节着磁层对流的速率，对建立地球空间环流模型至关重要。在近地等离子体中的电子散射率的量化也是很重要的了解电子通量和俯仰角分布在注入事件的演变，这提供了自由能源的激发波影响高能辐射带动态的来源。在地球上研究的重要物理过程可以应用于其他磁化行星，如木星和土星，在那里可以发生类似的散射。