A Statistical Study of the Sudden Impulses of Geomagnetic Field at Mid and Low Latitudes

Abstract:

Sudden impulses (SI) of geomagnetic field are associated with the sudden increases of the solar wind dynamic pressure, which is typically caused by the interplanetary shocks. In the mid and low latitudes at the ground, the SIs are the sudden increases of the northward magnetic field. Using a set of 447 SI cases and the SMR index (local Dst index provided by SuperMAG), we find that the responses of the geomagnetic field to the jump of the square root of solar wind dynamic pressure show a strong local time dependence with the strongest responses located in the midnight and the weakest responses located in the dawn side. We also find that geomagnetic responses, especially the noon and midnight responses, have quite different amplitudes under north and south interplanetary magnetic field. By calculating the normalized sudden impulses, we find that there is a seasonal variation with the peak around summer and the valley around winter. We also find that the shock normal orientation affects the amplitude of the sudden impulses: the more parallel the shock normal orientation is to the sun-earth line, the stronger the sudden impulses will be.