An Empirical Orthogonal Function Reanalysis of the Northern Polar External and Induced Magnetic Field During Solar Cycle 23
An Empirical Orthogonal Function Reanalysis of the Northern Polar External and Induced Magnetic Field During Solar Cycle 23
复制标题
太阳活动周期期间北极外部磁场和感应磁场的经验正交函数再分析 23
DOI：
10.1002/2017ja024420
复制
发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Shore R
中科院分区：
文献类型：
--
作者：
Shore R
我们将数据插值经验正交函数（EOFs）的方法应用到SuperMAG存档的地面磁矢量数据中，对整个北极地区11万km2等面积的箱面外磁场和感应磁场（SEIMF）进行了一系列月长度的再分析，这些箱面外磁场和感应磁场（SEIMF）在第23太阳周期（1997.0 - 2009.0）中以5分钟为周期。每次EOF再分析还将测量到的SEIMF变化分解成一个时空模式的层次，这些时空模式是根据它们对月磁场变化的贡献排序的。我们发现，领先的EOF模式都可以（主观地）解释为众所周知的SEIMF系统或其等效的电流系统。没有研究等效电流与实际电流的关系。我们通过月间空间相关性跟踪领先的SEIMF或类似类型的等效电流系统，并应用图论（客观地）分组它们在整个太阳周期中的外观和相对重要性，揭示季节和太阳周期变化。通过这种方式，我们确定了在一个太阳周期内对SEIMF变率贡献最大的时空模式。我们提出这种EOF和图论的结合，作为客观定义和研究SEIMF或其等效电离层电流的结构和变化的有力方法，可用于地磁和空间天气应用。这里是在太阳周期23上演示的，但可以扩展到有足够数据覆盖的任何时代。
We apply the method of data‐interpolating empirical orthogonal functions (EOFs) to ground‐based magnetic vector data from the SuperMAG archive to produce a series of month length reanalyses of the surface external and induced magnetic field (SEIMF) in 110,000 km2equal‐area bins over the entire northern polar region at 5 min cadence over solar cycle 23, from 1997.0 to 2009.0. Each EOF reanalysis also decomposes the measured SEIMF variation into a hierarchy of spatiotemporal patterns which are ordered by their contribution to the monthly magnetic field variance. We find that the leading EOF patterns can each be (subjectively) interpreted as well‐known SEIMF systems or their equivalent current systems. The relationship of the equivalent currents to the true current flow is not investigated. We track the leading SEIMF or equivalent current systems of similar type by intermonthly spatial correlation and apply graph theory to (objectively) group their appearance and relative importance throughout a solar cycle, revealing seasonal and solar cycle variation. In this way, we identify the spatiotemporal patterns that maximally contribute to SEIMF variability over a solar cycle. We propose this combination of EOF and graph theory as a powerful method for objectively defining and investigating the structure and variability of the SEIMF or their equivalent ionospheric currents for use in both geomagnetism and space weather applications. It is demonstrated here on solar cycle 23 but is extendable to any epoch with sufficient data coverage.