GEM Postdoc: Alfven Wave Coupling of Auroral Ionosphere with Magnetospheric Disturbances

众所周知，色散阿尔芬波是磁层和电离层耦合的最重要的过程之一。然而，赤道过程驱动剪切模态和挤压模态的机制尚不清楚。该项目将开发一个基于简化的双流体MHD公式（称为四场模型）的模拟模型，该模型包含平行离子流和可压缩性，以研究通过色散Alfven波的MI耦合。提出的研究有两个主要目标：1)在计算机模拟中实现地球磁场结构的非线性四场模型，以研究磁层扰动对极光电离层的影响；2)以高度模块化的方式开发代码，以便它可以耦合到其他模拟模型，如磁重联和气球不稳定性模型。四场模型的公式中包含了平行离子流，因此除了Alfven波印亭通量的能量输运外，还可以研究质量和动量输运形式的MI耦合。代码将被制作成发行版（一个包含代码本身、手册、变更日志和其他必要信息的包），以便想要使用它的研究人员可以下载它并在自己的平台上编译。作为模拟代码驱动的磁层扰动可以从磁尾模拟模型的输出或夜侧磁层的卫星观测中得到。预计该代码最终将被整合到地球空间环流模型（GGCM）中。这个工具在行星科学中同样有用，可以研究木星等其他磁化行星的类似物理过程。该提案为观测者提供了一个场所，让观测者自己运行代码，直接为数值模型做出贡献，这样他们就可以提供关于如何改进模型以更好地预测我们的地球物理环境的输入。开放使用政策具有教育方面的影响，因为它将使刚接触等离子体过程计算机建模的学生有机会自己查看代码并修改代码以适应自己的需要。

Dispersive Alfven waves are known to be one of the most important processes by which the magnetosphere and ionosphere are coupled. However the mechanisms by which shear and compressional modes are driven by equatorial processes is not well known. This project will develop a simulation model based on a reduced two-fluid MHD formulation (referred to as the four-field model) which incorporates parallel ion flow and compressibility to study the MI coupling via dispersive Alfven waves. The proposed research has two main targets: 1) to implement a nonlinear four-field model in computer simulation for Earth's magnetic field configuration to investigate effects of magnetospheric disturbances to the auroral ionosphere and 2) to develop the code in a highly modularized manner so that it can be coupled to other simulation models such as models for magnetic reconnection and ballooning instabilities. The four field model includes parallel ion flow in the formulation, and hence makes it possible to investigate MI coupling in the forms of mass and momentum transport in addition to transport of energy by Alfven wave Poynting flux. The code will be made into distributions (a package including the code itself, manual, change log, and other necessary information) so that researchers who would like to use it can download it and compile on their own platforms. The magnetospheric disturbances which are drivers of the simulation code can be taken from the output of magnetotail simulation models or satellite observations of the nightside magnetosphere. The code is expected to be eventually integrated into a Geospace General Circulation Model (GGCM). The tool can be equally useful in planetary sciences to study similar physical processes for other magnetized planets such as Jupiter. The proposal opens a venue for observers to contribute directly to numerical models by letting the observers run the code themselves so that they can provide input on how the model can be improved to better predict our geophysical environment. The open-usage policy has educational impacts because it will allow students new to the computer modeling of plasma processes a chance to look at the code themselves and modify the code to suit their own needs.