1 State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190, China; 
2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China

Two interplanetary shocks are examined to determine the responses of the magnetic field and plasma in the plasma sheet upon the shock impacts by using TC-1 observational data. The two shocks are observed by WIND on November 7, 2004. Prior to and after the shock, the IMF is either weakly southward or northward. The responses of the plasma sheet to the two shocks are intense and much similar. When the shock interacts with the magnetosphere, the magnetic field impulsively increases 1-2 min after the geomagnetic field sudden impulse (SI) judged from the Sym-H index change, and the magnetic field line is stretched. On the other hand, all of the ion density, the ion temperature, and the velocity of ion flow in the plasma sheet increase. Interestingly, quasi-periodical oscillations of the ion flow are suddenly enhanced, and the plasma flow is basically perpendicular to the local magnetic field. The responses of the magnetic field and the plasma are nearly simultaneous. The responses in the plasma sheet are probably caused by the lateral compression due to the dynamic pressure enhancement downstream the shock when the shock propagates antisunward in the magnetosheath.

This work was supported by the National Natural Science Foundation of China (Grant Nos. 40804046, 40890160 and 40731054), National Basic Research Program of China (Grant No. 2006CB806304) and the Specialized Research Fund for State Key Laboratories.