DYNAMICAL AURORAL MORPHOLOGY IN RELATION TO IONOSPHERIC PLASMA CONVECTION AND GEOMAGNETIC-ACTIVITY - SIGNATURES OF MAGNETOPAUSE X-LINE DYNAMICS AND FLUX-TRANSFER EVENTS

Ground-based observations of auroral, geomagnetic, and radar signature s of solar wind-magnetosphere coupling modes are presented. Two differ ent categories of ionospheric signatures are studied: (1) enhanced geo magnetic deflections and associated equatorward displacements of the c usp/cleft aurora and (2) a sequence of poleward moving amoral and geom agnetic events. It is suggested that signature 1 is mainly caused by d irectional. discontinuities in the interplanetary magnetic held changi ng the solar wind-magnetosphere coupling geometry and that signature 2 is caused by a recurring modulation of the reconnection rate at the d ayside magnetopause (flux transfer events (FTEs)), during the period o f strong coupling. The observed auroral and geomagnetic signatures are placed in the context Of plasma convection, as derived from magnetome ters in Svalbard, Greenland, and Canada, and the European incoherent s catter (EISCAT) radar. A suggestion for an ionospheric current system explaining the sequence of poleward propagating events, i.e., the FTE signatures, is presented.