Using OpenGGCM to Compute and Separate Magnetosphere Magnetic Perturbations Measured on Board Low Earth Orbiting Satellites
Using OpenGGCM to Compute and Separate Magnetosphere Magnetic Perturbations Measured on Board Low Earth Orbiting Satellites
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使用 OpenGGCM 计算和分离近地轨道卫星上测量的磁层磁扰动
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发表时间：
2017
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通讯作者：
J. Jensen
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作者：
J. Raeder;W. Cramer;K. Germaschewski;J. Jensen
我们使用开放地球空间大气环流模型（OpenGGCM）模拟来预测低地球轨道（LEO）卫星（如Swarm）在高纬度地区的磁场扰动。模拟使我们能够分离三种不同的主要贡献，观察到的扰动，即，由外磁层中的电流、场向电流（FACs）和电离层中流动的电流引起的扰动。我们发现，在500公里高度处，FAC的贡献最大，其次是电离层电流引起的扰动，而磁层电流的贡献较小。高纬度扰动在长时间的平静期内不会达到平均值。模式有很大的变化;然而，在大范围内，模式的基本形状保持稳定。因此，在没有明确地从数据中去除扰动的情况下，任何球谐函数拟合预计都会产生偏差。尽管预测的OpenGGCM扰动与Swarm数据相比并不特别好，但模拟再现了整体模式。然而，它们仍然可以用于减少系综的偏差，并通过产生其外部场贡献平均的系综来产生更好的全局球谐拟合。由于本文只触及外部场模型在产生无偏内部场模型中所起作用的表面，因此仍然有可能取得很大进展，例如通过改进外部模型，调查更大的合奏，并考虑地磁干扰时间的数据。
We use Open Geospace General Circulation Model (OpenGGCM) simulations to predict magnetic field perturbations at Low Earth Orbiting (LEO) satellites such as Swarm, at high latitudes. The simulations allow us to separate three different major contributions to the observed perturbations, i.e., the perturbations caused by currents in the outer magnetosphere, field-aligned currents (FACs), and the currents flowing in the ionosphere. We find that at an altitude of 500 km the strongest contribution comes from FACs, followed by the perturbations caused by the ionospheric currents, while the magnetospheric currents make only a minor contribution. The high latitude perturbations do not average out over extended quiet time periods. There are significant variations in the patterns; however, on a large scale, the basic shape of the pattern remains stable. Thus, without explicitly removing the perturbations from the data, any spherical harmonics fit is expected to incur a bias. Although the predicted OpenGGCM perturbations do not compare particularly well with Swarm data, the simulations reproduce the overall pattern. However, they may still be useful to reduce the bias of the ensemble and produce better global spherical harmonic fits, by producing an ensemble whose external field contributions average out. Since this paper only scratches the surface of the role that models of the external field can play in producing unbiased internal field models, much progress is still possible, for example by improving the external model, investigating larger ensembles, and by considering data from geomagnetically disturbed times.