Geosynchronous magnetopause crossings on October 29-31, 2003

During the period October 29-31, 2003, geosynchronous magnetopause crossings (GMC) have been identified based on the magnetic data of the GOES series spacecraft and plasma data of the LANL series spacecraft It is shown that most of the time the size of the dayside magnetosphere was highly decreased under the effect of very high pressure associated with high velocities and densities of the solar wind plasma, as well as high negative values of the B_z component of the interplanetary magnetic field (IMF). For tens of hours the subsolar magnetopause was deep inside the geosynchronous orbit. During the main phase and at the maximum of the strong geomagnetic storms that occurred in the period under consideration, the dayside magnetosphere was characterized by a strong dawn-dusk asymmetry, so that its size in the postnoon sector considerably exceeded the size in the prenoon sector. The geomagnetic disturbances in the morning on October 30 and 31, 2003 were accompanied by global magnetospheric pulsations with periods of 5-10 min and high amplitude (up to 0.8 R_E).