INTERBALL statistical study of ion flow fluctuations in the plasma sheet Original Research Article

We use ion distribution measurements with CORALL instrument on-board the INTERBALL/Tail spacecraft to study plasma flows in the mid-tail (−9 > X > −27 RE) plasma sheet. Three velocity components computed every 2 minutes exhibit two types of velocity variations: Earthward bursty bulk flows (BBFs) and random flow fluctuations. Their properties are in a good agreement with the observations of the ISEE-2 spacecraft (Borovsky et al., 1997). The INTERBALL/Tail spacecraft configuration favors measurements of Vz component, in contrast to previous experiments in which only Vx and Vy were measured reliably. In the outer part of the plasma sheet Vy and Vz fluctuations were close to each other (variances σ(Vy) and σ(Vz) were about 160 and 110 km/s, respectively), but in the inner part at the dusk flank amplitude of Vy fluctuations increased and was ∼ 2 times higher than that of Vz component. This asymmetry of fluctuations should be taken into account during modern theoretical analysis and simulations.