[P-EM09] Space Weather and Space Climate

[PEM09-12] Nighttime geomagnetic response to the jump of solar wind dynamic pressure

*Tian Zhang¹, Yusuke Ebihara¹ (1.Rish of Kyoto University)

Keywords:MHD simulation, Sudden commencement, geomagnetic disturbance

By performing a global magnetohydrodynamic (MHD) simulation, we investigated magnetic disturbances on the ground at high-latitudes for different types of jumps in the solar wind conditions, namely a sudden commencement (SC). We also calculated the resultant geoelectric field by the convolution method with an assumed ground conductivity in response to the solar wind jumps. We first demonstrated the maximum amplitude of the geomagnetic field disturbances as a function of magnetic latitude (MLAT) and magnetic local time (MLT), which is useful for specifying the hazardous area where the induced E field (geoelectric field) disturbances becomes large in response to the solar wind jumps. This map also helps us to better understand the generation of large geomagnetically induced currents (GICs) together with the information of the power grid. The evolution of the ionospheric Hall current, which is largely responsible to the magnetic disturbances, is well understood by the evolution of field-aligned currents (FACs). After the arrival of the solar wind jump, a pair of FACs (which are related to the preliminary impulse, PI) develop and travel in the antisunward direction. Soon after, another pair of FACs (which are related to main impulse, MI) travel in the antisunward direction. The MI-associated FACs remain strong as they propagate to the nightside, resulting in a positive (negative) excursion of the north-south component of the geomagnetic field at higher (lower) latitudes in the postmidnight sector. We discuss the variations of the geomagnetic field by comparing with observation.