EXPLORING THE MAGNETOSPHERIC BOUNDARY-LAYER

We show that, for most crossings of the low-latitude boundary layer, it is possible to define a parameter, based on electron density and temperature, which appears to track the transition from the magnetosheath to the magnetosphere. This "transition parameter" can be used to order other independent but simultaneous plasma measurements into well-defined patterns which are consistent from case to case. The method used to derive the transition parameter is presented here in full detail for the first time. The technique is applied to a set of six boundary crossings in order to demonstrate the consistency of the data when so ordered. We suggest that the transition parameter is intimately related to the structure of the boundary layer and discuss the implications for the physics involved. We conclude that there is a continuous change in the balance of processes which determine the structure of the layer and suggest, therefore, that there is no advantage in dividing the layer into different regions. We further conclude that simple mixing processes are the most important processes in that layer but that, at certain times and in some parts of the layer, more active processes must take place, since some quantities (e.g. magnetic field strength) reach extreme values within the layer.