On the spatio-temporal variations and causes of geomagnetic perturbations

Geomagnetically Induced Currents (GICs) is one important space weather phenomenon that occurs on the Earth surface which can adversely affect long-distance ground infrastructures such as oil pipelines and power cables. It is of great significance to study the causes of GIC and its relationship with solar wind conditions for the prediction of catastrophic space weather. Since GICs are closely related to geomagnetic perturbations, this paper uses long-term monitoring data from more than 100 geomagnetic ground stations in the Northern Hemisphere to statistically analyze the correlation between various solar wind parameters/geomagnetic indices and the geomagnetic perturbations as well as their time variations. Furthermore, using Space Weather Model Framework (SWMF), we simulate the distribution of geomagnetic disturbances in the Northern Hemisphere during the March 17, 2013 storm to understand the effects of various current systems on geomagnetic perturbations. The results show that: (1) The northward component of the geomagnetic perturbation B. during storm is highly correlated (CC=0. 75) with the SYM-H index which represents the intensity of ring current; the correlation is higher than that with the AE index and other solar wind parameters, indicating that the ring current is the main cause of the weakening of the northward magnetic field at middle and low latitudes; On the other hand, the eastward magnetopause current during quiet periods is the reason for the enhancement of the northward magnetic field at middle and low latitudes. (2) No strong correlation is found between the time variations of magnetic perturbations and solar wind flow pressure, interplanetary magnetic field Bs, substorm index AE, or geomagnetic storm index SYM-H. (3) The time variations of the magnetic perturbations at high latitudes is usually larger than that at lower latitudes, and such strong variations tend to occur during moderate storms or moderate/strong substorms. (4) SWMF model can capture northward geomagnetic perturbations during quiet time and eastward perturbations during storm time in general. (5) During magnetic storms, magnetosphere currents contribute most to the northward geomagnetic perturbations at middle and low latitudes, while at high latitudes the Hall current in the ionosphere is the dominant contributor. In addition, the eastern geomagnetic perturbations at high latitudes are mainly controlled by the Hall current, while that at middle and low latitudes are determined by field-aligned currents.