Data assimilation of low‐altitude magnetic perturbations into a global magnetosphere model
Data assimilation of low‐altitude magnetic perturbations into a global magnetosphere model
复制标题
将低空磁扰动数据同化为全球磁层模型
DOI：
10.1002/2015sw001330
复制
发表时间：
2016
期刊：
影响因子：
3.7
通讯作者：
Brian J. Anderson
中科院分区：
文献类型：
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作者：
V. Merkin;D. Kondrashov;Michael Ghil;Brian J. Anderson
电离层是地球磁层-电离层系统中唯一可以进行高时间分辨率和接近全球空间尺度的原位观测的区域。主动磁层和行星电动力学响应实验结合了Iridium®卫星的数据，提供了具有这种时空覆盖范围的磁场电离层测量结果。受此数据集出现的启发，我们在这里报告了将低空电离层磁扰动同化到里昂-Fedder-Mobarry（LFM）全球磁层模型与Rice对流模型（RCM）耦合的第一个结果。我们的同化方法依赖于赤道磁层压力和电离层区域2场向电流之间的准稳态线性近似关系的假设。这种近似是通过扰动赤道磁层压力傅立叶分解的大尺度模式和计算电离层磁场中相应模式的响应来数值实现的。通过使用所谓的“异卵双胞胎”类型的基于模型的同化测试来验证这种方法。在这种方法中，具有一组参数的LFM-RCM模型用于生成合成观测值，而具有不同参数的模型版本用于同化电离层观测值并计算磁层压力校正，然后将其应用于再现合成观测值。通过以预期方式修改电离层电流和磁扰动，具有同化合成数据的模型作出了正确的反应。因此，我们发现本文提出的方法是有前途的未来同化的真实的数据。
The ionosphere is the only region of the terrestrial magnetosphere‐ionosphere system where in situ observations with high temporal resolution and approaching global spatial scale are possible. Ionospheric measurements of magnetic fields with such spatiotemporal coverage have become available from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, combining data from the Iridium® satellites. Motivated by the emergence of this data set, we report here on the first results of assimilation of low‐altitude ionospheric magnetic perturbations into the Lyon‐Fedder‐Mobarry (LFM) global magnetospheric model coupled with the Rice Convection Model (RCM). Our assimilation approach relies on the assumption of a quasi‐steady, linear approximate relation between equatorial magnetospheric pressure and ionospheric Region 2 field‐aligned currents. This approximation is implemented numerically by perturbing large‐scale modes from the Fourier decomposition of equatorial magnetospheric pressures and computing responses of the corresponding modes in the ionospheric magnetic field. This methodology was validated by using model‐based assimilation tests of the so‐called “fraternal twins” type. In this approach, the LFM‐RCM model with one set of parameters is used to generate synthetic observations, while a model version with different parameters is used to assimilate the ionospheric observations and calculate the magnetospheric pressure corrections which are then applied to reproduce the synthetic observations. The model with assimilated synthetic data responded correctly by modifying ionospheric currents and magnetic perturbations in the expected way. We thus found the approach proposed herein to be promising for future assimilation of real data.