Large and sharp solar wind dynamic pressure variations as a source of geomagnetic field disturbances at the geosynchronous orbit

We present a comparison of large and fast solar wind dynamic pressure changes, observed by INTERBALL-1 satellite, with disturbances in the magnetospheric magnetic field measured by the GOES-8, 9 and 10 geosynchronous satellites. More than 300 solar wind pressure changes in the period from 1996 to 1998 were selected for this study. These fast and large solar wind pressure changes cause fast variations of the geomagnetic field magnitude in the outer magnetosphere. We found that increases (decreases) in the solar wind dynamic pressure always result in increases (decreases) in the geosynchronous magnetic field magnitude. The time delay between the solar wind pressure change and the geomagnetic response is significantly affected by the inclination of the pressure front to the Sun-Earth line. The amplitude of the geomagnetic field variation strongly depends on the location of the GOES satellite relative to the noon meridian, with the maximum amplitude near noon. (C) 2004 Elsevier Ltd. All rights reserved.