S3‐2 measurements of the polar cap potential

A total of 83 dawn‐dusk, high‐latitude passes of the S3‐2 satellite has been analyzed for the period August through December 1976 to determine correlations between the cross polar cap potential Φpc and various solar wind‐interplanetary magnetic field parameters. Hourly and 15‐s averaged values of the interplanetary magnetic field components and hourly averaged values of the solar wind velocity were available for 68 of the passes. In 41 (27) of the cases studied, the interplanetary magnetic field had a southward (northward) component. Measured potentials ranged from 170 kV during a substorm to 12 kV during two periods of northward interplanetary magnetic field. Least squares fits to the data were performed in order to determine the dependence of the polar cap potential on four different electric field models derived from reconnection theory and other traditionally correlated solar wind‐interplanetary magnetic field parameters. In each case, there is a residual polar cap potential of the order of 40 kV. This suggests a time delay in the relaxation of the potential when the interplanetary magnetic field turns northward and/or processes other than reconnection contribute to the polar cap potential. Total interplanetary magnetic field variance and solar wind speed were tested as filters on the data and found to have some significance. Comparisons with similar studies based on measurements from the Atmosphere Explorer and S3‐3 satellites are discussed.