Average profile of ion flow and convection electric field in the near-Earth plasma sheet

Two-dimensional distribution of ion flow and convection electric field in the near-Earth plasma sheet (9 < R < 30 R-E) is investigated on the basis of GEOTAIL measurements. Our statistics confirms that the observed ion flow in the plasma sheet is generally earthward, being accompanied by a significant dawn-to-dusk component which is distributed asymmetrically about the noon-midnight meridian. On the other hand, the convection electric field deduced from the V X B term after excluding the effects of ion pressure gradient drift shows much better symmetry about the noon-midnight meridian. Existence of significant difference between the ion and magnetic flux convection patterns suggests that the frozen-in condition does not hold in the near-Earth plasma sheet.