Comparison of ISEE‐1 and ‐3 interplanetary magnetic field observations

Abstract

Three hourly correlation coefficients and the lag at maximum correlation are computed using one minute averages of ISEE‐1 and ‐3 magnetometer data during the period in which ISEE‐3 moved from the earth to its halo orbit around the libration point. The maximum correlation coefficients are highly variable ranging from close to zero to almost unity. The lags, while on the average approximating the expected corotation delay, have very large departures from this value. These results suggest that the normals to the planes separating fields of differing orientation often make large angles to the ecliptic plane and/or that the interplanetary magnetic field has a significant amount of bending on a scale length the order of 200 earth radii. Furthermore, there often appears to be a significant amount of propagating structure in the IMF. Thus, ISEE‐3 magnetic field measurements should be used with caution if precise timing of arrival at the earth or precise directions of the field upon arrival are important.