Response of magnetic fields at geosynchronous orbit and on the ground to the sudden changes of IMF B _Z

The rapid change in the Earth's magnetosphere caused by solar wind disturbances has been an important part of the solar wind-magnetosphere interaction. However most of the previous studies focused on the perturbation of the Earth's magnetic field caused by solar wind dynamic pressure changes. In this paper, we studied the response of geosynchronous magnetic field and the magnetic field to the rapid southward turning of interplanetary magnetic field during the interval 1350-1420 UT on 7 May 2007. During this event, B _Z component of the interplanetary magnetic field decreased from 15 nT to -10 nT within 3 min (1403-1406 UT). The geosynchronous magnetic field measured by three geosynchronous satellites (GOES 10-12) first increased and then decreased. The variations of magnetic field strength in the morning sector (9-10 LT) were much larger than those in the dawn sector (5 LT). Meanwhile, the H components of geomagnetic field on the ground have similar response features but exhibit latitude and LT dependent variations. Compared with H components, the D components do not have regular variations. Although the solar wind dynamical pressure encounters small variations, the magnetic field both in space and on the ground does not display similar variations. Therefore, the increase of geomagnetic field in the dawn sector is caused by the southward turning of IMF (interplanetary magnetic field) B _Z . These results will help to better understand the coupling process of geomagnetic filed and interplanetary magnetic field.