Collaborative Research: CMG-- Models, Tools and Analysis for Studies of the Magnetosphere and Upper Atmosphere

该项目的目标是通过统计技术改进磁层、电离层和热层的电动力学行为模型，以找到未观测参数的最佳值。将估计三个这样的参数：1）电子能量和等离子体温度之间的比例系数; 2）将沉淀电子的通量与电子能量和等离子体密度相关联的参数;以及3）将穿过电势降的电子的能量增益与等离子体密度、电子能量和与磁场对准的电流的强度相关联的参数。虽然无法观测到这些参数，但可以通过将使用特定参数值生成的模型输出与适当的观测结果（例如，POLAR紫外成像仪看到的磁层风暴）进行比较来估计它们的最佳值。用于模拟磁层、电离层和热层的模型在计算上是昂贵的，因此只能测试有限数量的参数值。本研究将开发策略，基于分层统计建模和标量误差测量的发展，有效地搜索参数空间的最佳参数值。更好的电离层、磁层和热层模型无论是出于实际还是科学原因都很有意义。磁扰动期间的强电流加热了高层大气，使其向上膨胀，大大增加了卫星高度的空气密度，这会对卫星轨道产生重大影响。此外，电离层的电子密度在平静和扰动的日子都受到电场的强烈影响，这种密度的变化对用于通信和地理定位的卫星网络产生影响。因此，在这里进行的研究可有助于提高具有巨大实际效益的高层大气预报能力。

The goal of this project is to improve models of the electrodynamic behavior of the magnetosphere, ionosphere, and thermosphere through statistical techniques for finding optimal values of unobserved parameters. Three such parameters will be estimated: 1) a coefficient of proportionality between electron energy and plasma temperature; 2) a parameter relating the flux of precipitating electrons to the electron energy and the plasma density; and 3) a parameter relating the energy gain of electrons traversing a potential drop to the plasma density, electron energy, and the strength of the electric current aligned with the magnetic field. While these parameters cannot be observed, optimal values for them can be estimated by comparing model output generated using specific parameter values against appropriate observations (magnetospheric storms as seen by the POLAR Ultraviolet Imager, for example). Models used to simulate the magnetosphere, ionosphere, and thermosphere are computationally expensive, so that only a limited number of parameter values can be tested. This research will develop strategies, based on hierarchical statistical modeling and the development of scalar error measures, to efficiently search the parameter space for optimal parameter values. Better models of the ionosphere, magnetosphere, and thermosphere are of interest for practical as well as scientific reasons. Strong currents during magnetic disturbances heat the upper atmosphere, causing it to expand upward and greatly increase the air density at satellite altitudes, which can significantly affect the satellite orbits. In addition, the electron density of the ionosphere is strongly affected by the electric fields on both quiet and disturbed days, and variations in this density have impacts on satellite networks used for communication and geolocation. Thus, research conducted here could contribute to an upper-atmospheric forecasting capability of great practical benefit.