Relationship of total Birkeland currents to the merging electric field

The sun-synchronous orbit of the MAGSAT spacecraft has provided us with a new means to study the temporal response of large-scale Birkeland currents to variations in interplanetary parameters. We examined magnetic field data from 32 MAGSAT crossings of the northern auroral zone selected from 6 days in November and December, 1979. On each day at least 5 consecutive orbits were studied. The objectives of this study were to examine variations in the gross features of magnetic field disturbances observed on consecutive MAGSAT orbits, to investigate their relationship to interplanetary quantities, to estimate the total Birkeland current magnitude and correlate this current with various IMF parameters, and to study the relationship between the total Birkeland current and the inferred merging electric field E/sub M/. Inspired by recent calculations (Siscoe, 1982; Cornwall, 1982) a total Birkeland current (I/sub t/ot) versus E/sub M/ relationship was deduced. The results of our study indicate the following: (1) On an orbit-to-orbit basis, the most marked variation in the characteristics of the magnetic field disturbance was observed in amplitude rather than latitudinal width or location. (2) There is a consistently high correlation Rapprox.0.80 between either the observed average magnetic field disturbance ΔB or I/sub t/ot and various IMF parameters, with the highest correlation coefficient (0.82) for I/sub t/ot vs VB sin2 theta/2. (3) The fit of I/sub t/ot vs E/sub M/ allows us to estimate a total auroral zone conductance of approx.18.7 mho. (4) The functional relation I/sub t/ot = A(E/sub M/)/sup p/+B provided a good fit between I/sub t/ot and E/sub M/ for values of p ranging from 0.5 to 2.5, with the best fit for p = 1.0 to 5/3