Implications of the hydrodynamic analogue for the solar‐terrestrial interaction and the mapping of high latitude convection pattern into the magnetotail

Abstract

In the past, attempts have been made to relate magnetospheric geometry to that expected for the hydrodynamic analogue involving high speed flow past an obstacle. For this analogue, the region behind the obstacle can be divided into two distinct regions ‐ a separation bubble immediately behind the obstacle and a laminar wake further downstream. The purpose of this paper is to examine the implications of such an analogue in terms of convective flow patterns in the magnetotail and how these flow patterns might be expected to map down to ionospheric levels. We contend that magnetic field lines which thread the plasma mantle never reach the region of sunward convection normally associated with the auroral oval. We further claim that, during extended periods of southward interplanetary magnetic field, magnetic flux piles up near the poleward border of the morning sector auroral oval and that return flow occurs across the polar cap only after the interplanetary magnetic field turns northward. This effect should be observed in comparing the cross polar cap potential drop to the potential drop across the auroral oval for periods of northward and southward interplanetary magnetic field. Our model also explains the origin of field‐aligned currents and theta auroras in what would conventionally be called the polar cap.