Plasma entry from the flanks of the near-earth magnetotail: GEOTAIL observations in the dawnside LLBL and the plasma sheet

GEOTAIL data from the low-latitude flanks of the magnetotail at -30R(E) < X(GSM) < -15R(E) are analyzed. An example presented in this paper, which is representative of a group of the cases at the dawnside, shows that the region is characterized by highly varying magnetic field and the appearance of cold (<1 keV) and dense (>0.5/cc) plasma. While some of these cold-dense plasma are detected to flow tailward at 300-500 km/s, others are found to flow only slowly tailward or even sunward sometimes. Electrons of >100 eV are seen to be depleted in the tailward flowing part, suggesting that these data are taken when the satellite was located on open field lines. When the sunward flows are detected, the denisty tends to show an intermediate value, and thermal electrons (100-500 eV) are found to show bi-directional anisotropy. This suggests that part of the magnetosheath plasma is captured on closed field lines at the inner part of the low-latitude boundary layer (LLBL) in the tail flanks. Another study inside the plasma sheet at (X(GSM), Y-GSM) = (-17, -12)R(E) (a position well inside the magnetopause) shows a 2.5-hours period of the plasma sheet filled with cold (500 eV) and dense (2/cc) plasma. Bi-directional thermal electrons are seen to accompany this population. This may imply that relatively unheated plasma from the LLBL of the near-Earth magnetotail is filling a substantial part of the plasma sheet.