Response of the magnetic field in the geosynchronous orbit to solar wind dynamic pressure pulses

[1] We do a statistical survey of solar wind dynamic pressure (P-d) pulses and geosynchronous magnetic fields observed between 1998 and 2005. In geomagnetic quiet times with D-st > -50 nT, we find 111 solar wind dynamic pressure pulses which produce geosynchronous magnetic field responses. These responses are often observed by two or three GOES spacecraft at different local times in geosynchronous orbit. The magnitudes of the geosynchronous magnetic field changes (dB(z)) have a peak near the noon meridian, similar to the results obtained in the study of the response of the geosynchronous field to the large and sharp solar wind dynamic pressure variations. However, the relative change of the geosynchronous magnetic field dBz/AV-B-z (where AV-B-z is the average of the geosynchronous magnetic field Bz observed during the response to the pressure pulse) depends weakly on the local time; thus the change of B-z(dB(z)) is proportional to the average field (AV-B-z). As the magnitude of the relative change of solar wind dynamic pressure (dP(d)/P-d) increases, the rate of geosynchronous magnetic field variation increases correspondingly. These results imply that the magnitude of the geosynchronous magnetic field response could be determined by AV- B-z. In addition, the interplanetary field orientation does not affect the response significantly. Using an MHD code which models the global behavior of the solar wind-magnetosphere-ionosphere system, we reproduce the main characteristics of the observations.