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Determination of Electron Density Profile in the Magnetosphere Deduced from Propagation Characteristics of VLF Wave

根据甚低频波传播特性确定磁层电子密度分布

基本信息

批准号：
06452090
负责人：
KIMURA Iwane
金额：
$ 3.58万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06452090/
关键词：
Plasmasphere Wave propagation VLF wave Ray tracing Akebono Satellite Omega signal Electron density distribution Non-linear least square fitting

项目摘要

Determination of plasma density distributions in the plasmasphere and ionosphere has been attempted using wave normal vector direction and delay time of Omega signals observed on the Akebono satellite as well as the electron density along the satellite trajectory.The VLF receivers on board the satellite have enabled us to determine the wave normal direction and delay time of Omega signals continuously for more than one hour. The wave normal direction and delay time at the satellite location can also be calculated by three dimensional ray tracing technique, if the electron density distributions in the plasmasphere is known. Our method is to determine plasma parameters of assumed functions which represent the plasmasphere and ionosphere, so as to fit observed data as mentioned above with those calculated by ray tracing by using the assumed model.The procedure to find parameters of several functions mentioned above is the non-linear least squarefitting method so as to minimize the differences of these quantities between the observed and the calculated by ray tracing.For the plasma density distribution a diffusive equilibrium (DE) model with a positive ion temperature gradient with altitude is assumed. For the electron density profile below 1,000km of altitude, the altitudes of the F2 peak and the valley just above the E layr are determined from the IRI model.The validity of our plasmaspheric model based on the DE model was checked by comparing with SUPIM (Sheffield University Plasmaspheric and Ionospheric Model) , and we can conclude that our model is flexible enough to represent the general global distributions of the electron density in the plasmasphere. The reliability of our fitting algorithm was also checked by computer simulations, and we have confirmed that the global electron density distribution can be determined from the satellite wave data, without any significant error.

利用akakebono卫星上观测到的Omega信号的波法向量方向和延迟时间以及卫星轨道上的电子密度，尝试测定等离子体密度在等离子层和电离层中的分布。卫星上的VLF接收器使我们能够连续一个多小时确定欧米茄信号的波法向和延迟时间。如果等离子体层的电子密度分布已知，则可以利用三维射线追踪技术计算出卫星位置的波法向和延迟时间。我们的方法是确定代表等离子层和电离层的假设函数的等离子体参数，用假设模型将上述观测数据与射线追迹计算的数据拟合。求上述几个函数的参数的过程是非线性最小二乘拟合方法，以便使这些量的观测值与射线追踪计算值之间的差异最小。对于等离子体密度分布，假设了一个正离子温度随海拔梯度的扩散平衡模型。对于海拔1,000km以下的电子密度分布图，F2峰的高度和E层上方的谷的高度由IRI模型确定。通过与SUPIM （Sheffield University plasmaspheric and Ionospheric model）模型的比较，验证了基于DE模型的等离子体层模型的有效性，并得出结论：我们的模型具有足够的灵活性，可以代表等离子体层中电子密度的总体分布。通过计算机模拟验证了我们拟合算法的可靠性，我们证实了从卫星波数据可以确定全球电子密度分布，没有明显的误差。