Multi-point observations of cold-dense plasma sheet and its relation with tail-LLBL Original Research Article

Following the suggestion that the low-latitude boundary layer (LLBL) in the near-Earth magnetotail can be the site of capturing magnetosheath plasma into the plasma sheet during extended northward IMF periods, we have made a case study of the plasma sheet using data from WIND, Geotail and Akebono. On Feb. 9–10, 1995, IMF was northward for more than 24 hours. The plasma sheet at (Xgsm, Ygsm) = (−30 ∼ −15, 0 ∼ −10)Re observed by Geotail changed its status from hot-tenuous to cold-dense in this period. The ions in the cold-dense plasma sheet have two characteristic energies (temperatures) just as those in the LLBL. The colder component had a temperature as low as a few hundreds eV. From Akebono observations during the same time interval, the convection pattern in the high-latitude ionosphere was found to show a clear four-cell structure. Although these facts are well-known on statistical basis, the simultaneous observations definitely put a constraint that the plasma transport which produces the cold-dense plasma sheet should be in accord with the four-cell convection pattern. Inspection on the Akebono particle data shows that a few keV ion/soft (< 1 keV) electron precipitation are seen in the sunward convection zone located adjacent to the trapped particle region at invariant latitudes of 75° ∼ 80°. Discussion on the formation of the cold-dense plasma sheet during northward IMF period is made on the basis of these observations.