Abstract —The paper addresses the variability properties of the intensity and direction of the magnetic field during a substorm as well as magnetically quiet periods. The main focus is on the properties of the variations in the time derivative of the magnetic field d B / dt which are a factor of particular importance for the problem of the geomagnetically induced currents. A method of two- (2D) and three-dimensional (3D) diagrams is proposed for visual representation of the directional variations of a vector field. As an example, the geomagnetic field variations during the isolated substorm of October 17, 2015 are analyzed with the use of the chain of the IMAGE network magnetic stations. It is confirmed that d B / dt in the horizontal plane has a much stronger variability than the geomagnetic field perturbation Δ В . The proposed 3D diagrams show that the d B / dt polarization plane is inclined towards the Earth’s surface, which is probably due to the irregularity of the field of geomagnetic fluctuations.

中文翻译：

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基于极坐标图的地磁场变化分析

摘要 —本文讨论了在亚暴期间以及磁静区期间磁场强度和方向的可变性特性。主要关注的是磁场 d B / dt 的时间导数变化的特性，这是对地磁感应电流问题特别重要的一个因素。提出了一种二维 (2D) 和三维 (3D) 图的方法，用于矢量场方向变化的可视化表示。例如，利用 IMAGE 网络磁站链分析了 2015 年 10 月 17 日孤立亚暴期间的地磁场变化。证实了水平面的 d B / dt 比地磁场扰动 Δ B 具有更强的可变性。