Simultaneous solar-wind plasma and magnetic-field measurements in the expected region of the extended geomagnetic tail

A comparison is made of simultaneous plasma and magnetic-field measurements obtained by Pioneer 7 in the expected region of the geomagnetic tail at ∼1000 RE. The results indicate that, unlike the data for the near-earth (≤80 RE) geomagnetic tail, the data for the plasma and magnetic field have no unique signature of tail-associated phenomena. Furthermore, there are differences between the two types of data concerning the tentative identification of tail-associated phenomena for a number of intervals. The physical implications of these differences may be associated with anomalous transport properties that introduce turbulence in the form of mass diffusion and diamagnetic behavior adjacent to plasma eddies. As a result, the magnetopause, as it is recognized close to earth, loses its identity at far distances (>80 RE) and combines in a turbulent and hence ill-defined way with the geomagnetic tail. Thus there would be no reason to expect a consistent tail identification on a one-to-one basis with plasma and magnetic-field observations, the criterion presently used close to earth (i.e., <80 RE).