Statistical Study of the Solar Wind Deceleration in the Earth's Foreshock Region

The data from two same satellites (CLUSTER C1 and C3) were used to make a statistical study of the solar winddeceleration and deflection in the Earth's foreshockregion for the first time. In the foreshockcoordinates, the magnitude of deceleration is inversely proportional to the distance DBS between the satellite and the bowshock along the interplanetary magnetic field(IMF), and also inversely proportional to θBN, the angle between the IMF and the bowshock normal. The decelerations mainly occur when DWS, the distance from satellite to the ULF wave boundary along X direction, is less than 6Re. On the other hand, the solar winddeflection displays a similar feature. The largest values of deceleration and deflection are estimated as 10 km/s and 3°, respectively. These decelerations and deflections not only lead to a variation of the magnetopause's position and shape, but also provides a possible generation mechanism of the diffuse ions in the foreshockregion.