The plasmaspheric electric field as measured by ISEE 1


  • N. C. Maynard,

  • T. L. Aggson,

  • J. P. Heppner


Data from the double cylindrical probe electric field instrument on ISEE 1 has been analyzed to determine the average characteristics of the plasmaspheric electric field from L of 2–6. One year's data has been sorted and averaged covering all local times. The unaveraged electric field is highly variable, especially as magnetic activity increases. Typical magnitudes in the equatorial plane are between 0.2 and 0.8 mV/m in a frame corotating with the earth. During intense activity the electric fields become larger occasionally exceeding 2 mV/m. The average quiet electric fields are qualitatively in agreement with previous whistler and ionospheric radar measurements and also with representative ionospheric dynamo models. Under moderate and disturbed conditions the magnetospheric convection electric field penetrates inside the plasmasphere in the late evening and early morning sectors. A region of significant flow toward the prenoon magnetopause was detected postnoon, extending around toward dusk. This may be a substorm related effect. The electric field in the prenoon quadrant was small under most all conditions. Conversion of the electric field to flow velocities in the inertial frame shows that the plasma is moving in the direction of corotation at all local times in the inner plasmasphere. In the evening sector the flow velocity is reduced, and in the morning sector it is enhanced as convection penetrates the outer L shells. A mixed behavior is seen in the afternoon hours.