Dense plasmas in the distant magnetotail as observed by GEOTAIL

Abstract

It is found that dense plasma is a very common plasma regime in the earth's magnetotail, especially beyond 150RE behind the earth. Plasma density in the tail lobe inferred from spacecraft potential measurements is often comparable with that in the tail current sheet. This observation suggests that the tail lobe is rich in cold plasmas. In the distant current sheet, plasma density sometimes exceeds 1 cm−3. The high‐density current sheet accompanies northward magnetic field, coming out from both the dawn and dusk tail flanks. Two possible models are discussed; one is highly stretched LLBL (low latitude boundary layer) that spreads to the whole current sheet in the distant tail, and the other is disappearance of the distant magnetotail during northward IMF.