SAPS measurements around the magnetic equator by CRRES

Enhancements of convection electric fields during two substorms have been analyzed using CRRES satellite data measured in the premidnight inner magnetosphere. The electric field, related to subauroral polarization streams (SAPS), begins to increase within 30 sec after the substorm onset, indicating a quicker response of convection in the inner magnetosphere to substorms than has been reported (similar to 10 min) before. A prompt response of the ion pressure and the following decrease in the cold plasma density supports the fact that the electric field enhances just after the substorm onset and drives accelerations of energetic ions and plasmapause erosion. The SAPS electric field enhances between the earthward edges of the ring current and plasmasheet, and the plasmapause coincides with the earthward edge of the electron plasmasheet. The plasmapause location deviates from the stagnation point, and the SAPS electric field penetrates into the plasmasphere, driving a sunward plasma drift of the plasmaspheric plasma.