Simultaneous Cluster and IMAGE observations of cusp reconnection and auroral proton spot for northward IMF

On March 18, 2002, under northward interplanetary magnetic field (IMF) and high (∼15 nPa) solar wind dynamic pressure conditions, Cluster observed reconnection signatures and the passage of an X‐line at the large (∼175°) magnetic‐shear high‐latitude magnetopause (MP). The observations are consistent with the occurrence of a reconnection site tailward of the cusp and in the vicinity of the spacecraft. At the same time IMAGE observed a bright spot poleward of the dayside auroral oval resulting from precipitating protons into the atmosphere. The intensity of the proton spot is consistent with the energy flux contained in the plasma jets observed by Cluster. Using the Tsyganenko‐01 magnetic field model with enhanced solar wind pressure, the Cluster MP location is mapped to the vicinity of the IMAGE proton spot. Mapping the auroral spot out to the MP implies an X‐line of at least 3.6 R E in y GSM . In addition to confirming the reconnection source of the dayside auroral proton spot, the Cluster observations also reveal sub‐Alfvénic flows and a plasma depletion layer in the magnetosheath next to the MP, in a region where gas dynamic models predict super‐Alfvénic flows.