Reconnection driven lobe convection: Interball tail probe observations andglobal simulations

We present Interball Tail Probe observations from the high latitude mid-tai l magnetopause which provide evidence of reconnection between the interplan etary magnetic field (IMF) and lobe field lines during a 6 h interval of st able northward and dawnward IMF on October 19, 1995. Results from a global magnetohydrodynamic simulation for this interval compare well with the Inte rball observations. With the simulations, we provide an extended global vie w of this event which gives us insight into the reconnection and convection dynamics of the magnetosphere. We find that reconnection occurs in a regio n of limited spatial extent near the terminator and where the IMF and the l obe field are anti-parallel. Reconnected IMF field lines drape over the day side magnetosphere, convect along the flanks into the nightside, and enter the magnetotail through a small entry window that is located in the flank o pposite to the reconnection site. Ionospheric convection is consistent with previous observations under similar IMF conditions and exhibits a two cell pattern with a dominant lobe cell over the pole. The magnetic mapping betw een the ionosphere and the lobe boundary is characterized by two singularit ies: the narrow entry window in the tail maps to a 6 h wide section of the ionospheric lobe cell. A singular mapping line cuts the lobe cell open and maps to almost the entire tail magnetopause. By this singularity the magnet osphere avoids having a stagnation point, i.e., the lobe cell center maps t o a tailward convecting field line. The existence of singularities in the m agnetic mapping between the ionosphere and the tail has important implicati ons for the study of tail-ionosphere coupling via empirical magnetic field models. Because the lobe-IMF reconnection cuts away old lobe flux and repla ces it with flux tubes of magnetosheath origin, solar wind plasma enters th e lobes in a process that is similar to the one that operates during southw ard IMF. (C) 2000 Elsevier Science Ltd. All rights reserved.