Plasma sheet fine structure at high latitude



[1] High-resolution ion observations made in recent years, by the TIMAS instrument on the Polar satellite and other instruments, reveal a dynamic and finely structured plasma sheet, at least at high latitude. This study invokes multipoint Cluster observations with the CIS CODIF instruments (ion composition and distribution function) to determine whether transverse density gradients can be of the order of keV proton gyroradii scale size, as suggested by the TIMAS observations. It is shown that the plasma sheet is indeed prominently filamentary and that the proton density with 40 eV ≤ E ≤ 40 keV can vary by Δn = 0.4 cm−3 across less than five average proton gyroradii at R ≈ 5 RE (average E ≈ 7.5 keV at the time). This compares favorably with typical 10-km-size (or less) auroral structures when projected earthward.