Dayside auroral bifurcation sequence during B-y-dominated interplanetary magnetic field: Relationship with merging and lobe convection cells

We report observations in the cusp region of synchronous activations of lat itudinally separated auroral forms ("bifurcations") occurring in a sequence and interpret the observations in terms of an intermittent magnetic reconn ection process at the dayside magnetopause proceeding in a wave-like manner from lower to higher latitudes, The observations refer to a B-y-dominated interplanetary magnetic field (IMF) orientation, Optical auroral observatio ns are combined with radar observations of ionospheric ion drift to illustr ate the association between the aurora and plasma convection in two cases r epresenting positive and negative IMF B-y conditions. In the meridian photo meter scans, each individual event in the sequence appeared as an initial b rightening in the south (type 1), followed by a second brightening/expansio n farther to the north (type 2). The events occurring during all eastward p ointing (B-y>0) IMF are observed typically to expand westward across the 12 00 magnetic local time meridian, from the postnoon to the prenoon side. The higher-latitude, type 2 activity is associated with strong westward convec tion, which we identify to be part of a lobe cell, while the equatorward bo undary intensifications (type 1) occur in the region of a merging cell, dis torted by the prevailing IMF B-y condition. The auroral sequence consists o f several paired activation events, typically recurring at similar to 5- to 10-min intervals, and each individual event lasting similar to 10 min. The ion drift observations are found to be consistent with recent MHD modeling results on IMF magnetosphere interconnection geometry and the associated c omposite pattern of merging and lobe convection cells in the cusp region, T he ground observations reveal the intermittent nature of two components of cusp region particle precipitation and the association between the correspo nding type 1 and 2 auroras and merging and lobe convection cells, respectiv ely.