Magnetospheric Mass Density Model

磁层质量密度控制着磁层对外部和内部作用力的时间响应，因此对于理解和预测突发脉冲和超低频（ULF）波等时间相关现象的影响非常重要。这些动态过程可导致辐射带粒子加速或损失。在本项目中，航天器对环形阿尔芬波的观测将用于评估磁层质量密度，并开发一个模型，将密度的赤道分布和场线分布描述为描述磁层状态的参数的函数。主要利用的航天器观测是GOES、CRRES、Polar和AMPTE/CCE航天器的磁场和电场测量，以及LANL地球同步卫星的速度矩测量。除了航天器对Alfven波的观测外，现场电子密度（CRRES和Polar）、现场粒子数据（LANL地球同步卫星）和地面磁力计数据将用于验证模型并评估平均离子质量。目前的质量密度反演技术包括可调磁场模型和多谐频率输入，以获得质量密度的场线依赖关系。本项目将考虑的具体问题是：(1)什么是磁层中的质量密度，它如何依赖于L壳、磁性局地时间MLT、由Dst、Kp等地磁指数指定的磁层状态，以及由太阳风速度和动压等参数指定的太阳风条件，以及质量密度在太阳活动周期内如何变化？(2)质量密度沿磁力线的分布是怎样的？决定这种分布的物理过程是什么？在什么条件下，磁极赤道的局部密度会达到峰值？(3)圆环Alfven波的质量密度与电子密度是否一致？重离子对质量密度的贡献是什么？这种贡献如何依赖于磁层的状态？什么物理过程导致重离子在磁赤道积聚？(4)如果将地面位置映射到航天器位置，在地面测量的环面Alfven频率与在空间测量的频率是否一致？

Magnetospheric mass density controls the time response of the magnetosphere to external and internal forcing, and is thus important for understanding and predicting the effects of time dependent phenomena such as sudden impulses and Ultra-Low Frequency (ULF) waves. These dynamic processes can lead to acceleration or loss of radiation belt particles. In this project, spacecraft observations of toroidal Alfven waves will be used to evaluate the magnetospheric mass density and to develop a model to describe both the equatorial and field line distribution of the density as a function of parameters describing the state of the magnetosphere. The main spacecraft observations to be used are magnetic and electric field measurements by GOES, CRRES, Polar, and AMPTE/CCE spacecraft, and velocity moment measurements by LANL geosynchronous satellites. In addition to spacecraft observations of Alfven waves, in-situ electron density (CRRES and Polar), in-situ particle data (LANL geosynchronous satellites), and ground magnetometer data will be used to validate the model and evaluate the average ion mass. State of the art techniques for mass density inversion include adjustable magnetic field models and multi-harmonic frequency input to get the field line dependence of the mass density. Specific questions that will be considered as part of this project are: (1) What is the mass density in the magnetosphere, and how does it depend on L shell, the magnetic local time MLT, the state of the magnetosphere as specified by geomagnetic indices such as Dst, Kp, and the solar wind condition as specified by parameters such as the solar wind velocity and dynamic pressure, and how does the mass density vary during the solar cycle? (2) What is the distribution of mass density along magnetic field lines and what are the physical processes that determine this distribution? Under what conditions is there a peak in local density at the magnetic equator? (3) Is the mass density inferred from the toroidal Alfven waves consistent with the electron density? What is the contribution of heavy ions to the mass density, and how does this contribution depend on the state of the magnetosphere? What physical processes cause the accumulation of heavy ions at the magnetic equator? (4) Are toroidal Alfven frequencies measured on the ground consistent with those in space if the ground location is mapped to the spacecraft location?