Research On Interplanetary Sources Of Geomagnetic Induced Current Disturbances

The dramatic change of the geomagnetic fields is able to trigger geomagnetically induced currents(GIC)in the transmission lines,the neutral-grounded transformer and the earth circuit,which may have a disastrous impact on the ground-based technical system.Therefore,GIC disturbance is one of the most important space weather phenomena affecting the human ground-based technical system.In this dissertation,using the routine GIC data detected from the natural gas transmission pipelines in the high-latitude Finland M?nts?l? area during nearly two solar cycle periods(1999-2017),the characteristics of GIC disturbance distribution,the distribution of strong GIC disturbance events and their interplanetary sources,are statistically investigated.Furthermore,we preliminarily analyzed the characteristics of GIC disturbance triggered by interplanetary shock,as well as its possible physical triggering mechanism.The results are as follows:The GIC with intensity distributed between 0 A and 1 A is found in 95% of the time period.The probability of GIC disturbance,defined asmaxGIC(29)1A,occurring near the local magnetic nightside is the highest,which is possibly related to the ionosphere current disturbance during the magnetospheric substorm.Here we have identified 91 strong GIC disturbance events(defined asmaxGIC(29)10A)during near 18 years between 1999 and 2017.It is found that there are more significant GIC disturbance events in the 23 rd solar cycle than in the 24 th solar cycle,which is consistent with the frequent occurrence of solar wind disturbance events and strong magnetospheric disturbance events during the 23 rd solar cycle.In addition,strong GIC disturbance events occur more frequently in the declining phase than in the rising phase of solar cycle.It is found that the interplanetary corona mass ejections,and their driven shocks and the sheath plasma,and stream interaction regions are the main interplanetary sources of strong GIC disturbance events.Except for the shock-driven strong GIC disturbance events,all the other strong GIC disturbance events occurred during the main phase and the recovery phase of the magnetic storm.It is concluded that,storm is the necessary condition of the occurrence of strong GIC disturbance events.However,the corresponding GIC intensity peak is weakly correlated with the intensity of the magnetic storm.When the interplanetary shock impinges on the magnetosphere,the magnetospheric compression would trigger sudden and dramatic changes of the geomagnetic field,and cause disturbances in nearly all the plasma areas in themagnetosphere-ionosphere coupling system.We statistically analyzed the distribution characteristics of the GIC disturbance caused by interplanetary shocks.The interplanetary shock triggers a sudden increase(SI(10))in the magnetic field,which subsequently causes GIC disturbances.In terms of morphology,the GIC disturbance has three types of variation characteristics: bipolar structure,oscillation type,and unipolar type.Bipolar structural events account for 52.80% of all events,and the changes in GIC of these events are strongly correlated with SI(10)changes,mainly in the morning and dusk side.In the morning side,the bipolar disturbance is dominated with the direction change from west to east,while in the dusk side,the bipolar disturbance mainly shows its directional change from east to west.The bipolar polarity change of the GIC is caused by the bipolar variation of high latitude geomagnetic field disturbance.The SC model of geomagnetic field established by Araki et al.can be used to explain the opposite polarity direction of GIC disturbance in the morning and dusk side.In comparison,oscillatory GIC disturbance mainly occurs on the day side and unipolar GIC disturbance mainly occurs on the night side.The specific physical mechanism needs to be further studied.These results give us a more comprehensive understanding of high-latitude GIC disturbances,and help us to understand the physical mechanism of their formation.It also lays a foundation for the establishment of physical model of GIC intensity prediction for the sake of reducing its damage to human activity.