Dynamic Cusp Aurora And Associated Pulsed Reverse Convection During Northward Interplanetary Magnetic Field

We report a study of ionospheric signatures of plasma entry and momentum transfer at the dayside magnetopause during northward oriented interplanetary magnetic field (IMF), combining ground observations of the dayside aurora, and ionospheric ion drift (CUTLASS HF radar) with simultaneous particle precipitation data obtained from three overflights by the Defence Meteorological Satellite Program (DMSP) F12, F13 and F14 spacecraft. The observations were taken during a 37-min long interval of strongly northward IMF (B-z=7 nT; clock angle similar to 10 degrees-15 degrees) after a. rapid northward turning. The meridan scanning photometer at; the ground station recorded a long stepwise poleward retraction and latitudinal widening of the band of auroral emission in the cusp region. Thus the activity includes a series of episodes which are characterized by an initial 1-2 min poleward "step" of the auroral poleward boundary, followed by a similar to 3-4 min period of relatively steady auroral latitude. The auroral events were accompanied by bursts of "reverse" two-cell convection characterized by equatorward flow across the cusp poleward boundary. The three DMSP spacecraft, which traversed the poleward boundary of the cusp aurora from north to south, entered into a region of auroral precipitation where electrons and ions of magnetosheath origin were present, together with equatorward convection. The observations are found to be consistent with a theoretical description of a sequence of bursts of lobe reconnection involving both hemispheres. This process results in the capture of magnetosheath flux tubes and thereby closed flux is added to the dayside magnetosphere.