The deflection of the earthward flow observed by TC-1 in the near magnetotail

Using the data observed by the TC-1 satellite in the magnetotail season from 2004 to 2007, we extended the earthward high-speed flow to the lower speed and statistically investigated its spatial evolution in the geocentric distances between -13.4R_E and -5R_E. Our findings are as follows: (1) When the earthward flow are moving close to the earth, the occurrence rate of the earthward flow decreases mainly around the sun-earth line, the occurrence rate in the dawn and dusk flank does not fall but rise, the highest occurrence rate locates in the dusk flank, which may indicate that the earthward flow is deflecting to the dawn and dusk flank under its process penetrating to the earth. (2) Closer to the earth, the amplitude of V and V_x is smaller; there are slight variations of V_y and V_z and their distributions are dawn-dusk asymmetry; which indicates that the process penetrating to the earth is accompanied by the dawn-dusk and north-south deflection. (3) During the earthward flow, the plasma density is relatively small on the whole; it gradually increases with the decrease of the geocentric distances. (4) The distribution of the parallel and perpendicular flow speed is dawn-dusk asymmetry. The parallel speed in the dawn is larger than that in the dusk. The perpendicular speed in the dusk is larger than that in the dawn. Considering that the large perpendicular flow speed is easy to trigger the instability closely related to the current disruption, we infer that the current disruption occurs easily in the dusk. (5) The magnetic pressure is mostly dominant with few thermal pressures comparable to the magnetic pressure. The total pressure is large near the sun-earth line and small in the dawn and dusk, so large pressure gradient forms both in the dawn and dusk direction; which cause the earthward flow deflect and the occurrence rate increase in the dawn and dusk flank. Lower pressure than the ambient can be observed in the dawn and dusk flank close to the earth, and that can be observed farther away from the earth around the sun-earth line; which suggest that the current disruption occurred at different locations in the past cases may be caused by the pressure distribution close to the earth.