A correlative study of magnetic flux transfer in the magnetosphere

The applied magnetic flux (Φap) of the southward component of the interplanetary magnetic field in GSM coordinates (Bz−) which impinges upon the sunward magnetopause has been compared with the time integral of the auroral AL index during 56 intervals within a 3‐month period in 1969 when interplanetary records from Heos 1 and Explorer 35 were available. The periods of magnetic activity chosen were those for which Bz > 0 and AL < 20 γ at the beginning and end of the interval. It was found that for these intervals, ∫ AL dt ∝ Φap with a correlation coefficient of 0.94. In addition, the empirical relationships between magnetic flux transfer, the applied southward flux, and ∫ AL dt arrived at by Holzer and Slavin (1978) on the basis of expansions and contractions of the forward magnetosphere observed with Ogo 5 are reexamined and improved. With these expressions describing the bulk rates of magnetic flux transfer within the magnetosphere a lower limit of 0.2±0.1 on the local reconnection efficiency at the magnetopause is calculated.