GEM: Quantifying the Rate of Diffuse Auroral Electron Precipitation

漫射极光降水为地球上层大气提供了能量输入的主要来源。沉淀的粒子导致电离速率的变化，这可以调制大的自然电流系统，并沿传输线和管道感应电流。额外的电离也会导致中性大气的化学变化，这与臭氧消耗有关。沉淀的粒子还导致电离层电导率的变化，这种电导率沿磁力线映射，并进一步影响等离子体在磁层中的传输。弥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。因为磁层基本上是无碰撞的，所以唯一可能导致俯仰角散射的机制是波-粒子相互作用。以前的研究表明，静电电子回旋谐波(ECH)波和哨声模式合唱的散射可能是重要的，但对于主导过程仍然没有普遍的共识。本项目将通过研究ECH波和合唱波引起的粒子散射的速率来研究ECH波和合唱波的作用。将根据对CRRES卫星在不同磁活动水平下在外层磁层观测到的和声和ECH波的频谱特性的综合分析，利用现有的程序计算俯仰角扩散率。计算的电子散射率将被用来确定平衡俯仰角分布和与强扩散施加的限制相比对大气的降水损失率。散射结果将与近地等离子体片中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。这项研究将提供对微物理过程如何调节地球空间中的能量转移的定量理解。拟议的研究是新的宝石专题小组关于极光弥漫降水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承担。所获得的科学成果将提供给对不同地磁条件下的环流电子总数和弥散极光降水的全球分布进行建模的磁层界其他成员。这项研究的结果可用于模拟电离层电导率的全球分布，电离层电导率调节磁层对流的速度，这对地球空间大气环流模式的发展至关重要。近地等离子体片中电子散射率的量化对于理解注入事件期间电子通量和俯仰角分布的演变也是重要的，这为影响高能辐射带动力学的波的激发提供了自由能源。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，在那里可能发生类似的散射。

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.