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Empirical orthogonal function analysis and modeling of global ionospheric spherical harmonic coefficients
GPS Solutions ( IF 4.9 ) Pub Date : 2020-04-29 , DOI: 10.1007/s10291-020-00984-1
Peng Chen , Hang Liu , Yongchao Ma

We developed a global empirical model for computing spherical harmonic (SH) coefficients based on the empirical orthogonal function (EOF) method and periodic functions by utilizing global ionospheric SH coefficients data provided by Center for Orbit Determination in Europe (CODE) during the years 2005–2016. Results show that the first four-order base functions and corresponding associated coefficients can represent 97.15% of the basic characteristics of the original data. The first four-order associated coefficients have noticeable periodic variations, and the correlation between these coefficients and the solar activity intensity is high. By fitting the associated coefficients with the periodic function that takes into account the influence of solar activity, it is possible to establish an EOF model to characterize the variations of the ionospheric SH coefficients with few model parameters and further calculate the global vertical total electron content (VTEC). Relative to the existing global VTEC EOF models, this EOF method can achieve high-accuracy modeling of global VTEC with a smaller number of model coefficients. By comparing the SH coefficients and the global VTEC between the EOF model and CODE, results demonstrate that the EOF model can achieve high accuracy and reliability under different solar activities. The difference between the EOF model and CODE is basically at the same level as that between the individual ionospheric analysis centers and CODE. In the extreme event of magnetic storms, the EOF model can also present higher accuracy than the international reference ionosphere (IRI) model.

中文翻译:

全球电离层球谐系数的经验正交函数分析与建模

我们利用经验正交函数(EOF)方法和周期函数,通过利用欧洲轨道确定中心(CODE)在2005年提供的全球电离层SH系数数据,开发了一个用于计算球谐(SH)系数的全局经验模型。 2016。结果表明,前四阶基本函数和相应的相关系数可以代表原始数据的97.15%。前四阶相关系数具有明显的周期性变化,并且这些系数与太阳活动强度之间的相关性很高。通过将相关系数与考虑太阳活动影响的周期函数拟合,可以建立一个EOF模型,用很少的模型参数来表征电离层SH系数的变化,并进一步计算全局垂直总电子含量(VTEC)。相对于现有的全局VTEC EOF模型,此EOF方法可以使用较少的模型系数来实现全局VTEC的高精度建模。通过比较EOF模型和CODE之间的SH系数和整体VTEC,结果表明EOF模型可以在不同的太阳活动下实现高精度和高可靠性。EOF模型和CODE之间的差异基本上与单个电离层分析中心和CODE之间的差异相同。在电磁风暴的极端情况下,EOF模型也可以提供比国际参考电离层(IRI)模型更高的准确性。
更新日期:2020-04-29
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