Viscous Interaction between the Solar Wind and the Magnetosphere

Abstract

With the discovery of the magnetospheric low latitude boundary layer (LBL) at least partly on closed geomagnetic field lines it is becoming apparent that viscous effects are due to the LBL acting as a dynamo. As such, viscous interaction will reflect the observed dependence of the LBL on the interplanetary magnetic field (IMF); it does have a dependence on the IMF, in contrast to what is commonly assumed. The massive tailward flow requires polarization of the layer: plasma on closed field lines has to do work to maintain its momentum. A by-product is the convection in the plasma sheet and the inner magnetospheric, resulting in auroral phenomena. The most urgent question for solar wind-magnetospheric interaction is the mechanism for the transfer of solar wind plasma through the magnetopause onto closed field lines. The process cannot be steady state reconnection, since the reconnected field lines would be open. The same is true of flux transfer events as commonly viewed; it is serious mistake to try to explain a localized and time-dependent process with a constant electric field, hence zero curl. We must include an inductive electric field according to Faraday's law with a finite curl (by definition) and thus an electromotive force. The plasma can respond by a polarization electric field, which has curl E=0; the latter property means that the polarization of the plasma cannot affect the electromotive force of the induction field. Elementary analysis shows that this can result in plasma flow onto closed field lines. Now what we have is a plasma transfer event (PTE). This process is a form of transient reconnection (preferably called merging to distinguish it from the steady state process usually called reconnection). Thus, when viewed on a broad scale there is a synthesis between merging (reconnection) and viscous interaction, but both processes have changed considerably from the ones proposed years ago.