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We report observations of a sharp spatial boundary between the outer plasma sheet and the inner magnetosphere. It was successively crossed by the Cluster spacecraft in their pearl-on-string configuration near the perigee (∼4 Re) at midnight during a substorm expansion phase. Being mapped presumably to 8-10 Re in the equatorial tail, this boundary was extremely thin, comparable to a gyroradius of plasma sheet proton. Substantial changes on this spatial scale were observed coherently in (1) the fluxes of radiation belt energetic electrons (exceeding a factor 10 at E ≥ 100 keV), (2) the plasma pressure (by a factor of 2), (3) the density and outflow of the cold ionospheric plasma. Strong diverging electric field (azimuthal shear flow) coincides with this boundary and is accompanied by a strong downward field-aligned current. While this boundary was staying at nearly the same location during the ∼5 min time scale, we also found indications of its dynamical origin. We suppose it could be generated by a sudden braking and azimuthal deflection of localized bursty fast flows produced by the magnetic reconnection which was going on at this time in the near tail.
Original language | English |
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Article number | 1799 |
Pages (from-to) | SSC 3-1 - 3-4 |
Number of pages | 4 |
Journal | Geophysical Research Letters |
Volume | 30 |
Issue number | 15 |
DOIs | |
State | Published - 6 Aug 2003 |
ID: 36755088