INTERBALL statistical study of ion flow fluctuations in the plasma sheet

Abstract

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 R E ) 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 V z component, in contrast to previous experiments in which only V x and V y were measured reliably. In the outer part of the plasma sheet V y and V z fluctuations were close to each other (variances σ( V y ) and σ( V z ) were about 160 and 110 km/s, respectively), but in the inner part at the dusk flank amplitude of V y fluctuations increased and was ∼ 2 times higher than that of V z component. This asymmetry of fluctuations should be taken into account during modern theoretical analysis and simulations.