Parallel-dominant and perpendicular-dominant components of the fast bulk flow: Comparing with the PSBL beams

Utilizing multipoint observations by the Cluster satellites, we investigated the ion distributions of the fast bulk flows (FBFs) in the plasma sheet. Simultaneous observation by C1 and C3 revealed that parallel-dominant and perpendicular-dominant components of the flows coexist and correspond to B_x-dominant and B_z-dominant magnetic field regions within the FBFs, respectively. In both cases, the ions distributions are characterized by a single-beam/crescent shape. In particular, no reflected ions are found within the FBFs. Statistical analysis showed that within the FBFs, the strength of the B_x component is typically less than 5nT for B_z-dominant regions and above 10nT for B_x-dominant regions. To distinguish between the parallel-dominant component of the FBFs and the field-aligned beams in the plasma sheet boundary layer (PSBL), we further statistically analyzed the tailward parallel flows (TPF) with positive B_z in the plasma sheet. The results indicated that the FBFs tend to have higher velocity, weaker B, and higher magnetic tilt angle (θ_MTA) than the TPFs/PSBL beams. Statistically, in the region of B>30nT (θ_MTA>10°), only PSBL beams can be observed, while in the region of BMTA>30°), the FBFs are dominant. In the intermediate region (10°MTA