Abstract. The Interball spacecraft configuration favors, in contrast to previous experiments, investigation of vertical ion flows (GSM V_z ). We use measurements of the CORALL instrument for the statistical study of V_z and V_y plasma flows in the mid-tail plasma sheet. In agreement with the previous observations, the mean V_y was positive on the dusk side and negative on the dawn side. When IMF was southward, the mean V_z consisted of the convection flow towards the equatorial plane ~ 7 km/s and the northward flow ~ 8 km/s. When IMF was northward, both components nearly vanished. The velocity variance was much larger than the mean values. The V_z variance maximized on the dawn flank and was always 15–20% smaller than the V_y one. The V_y variance maximized in the pre-midnight sector closer to the neutral sheet. We conclude that velocity fluctuations are composed with the inherent high-beta plasma turbulence contributing to all components, and the BBF-related activity contributing mainly to V_y in the pre-midnight plasma sheet.

Key words. Magnetospheric physics (magnetotail; plasma sheet; plasma convection)