Spatial scale of high‐speed flows in the plasma sheet observed by Cluster

Spatial gradients of high‐speed flows in the midtail plasma sheet are determined using multipoint observations from the Cluster spacecraft along the “dawn‐dusk” direction (perpendicular to the main flow and in the plane of the tail current sheet) and along the north‐south direction. If we take the average or median of the spatial gradients and assume that the flow channel has a linear gradient, these values suggest that the full width of the flow channel is 2–3 R E in the “dawn‐dusk” direction and 1.5–2 R E in the north‐south direction. The velocity gradient at the duskward edge of a flow tends to be sharper than that at the dawnward edge, possibly reflecting an asymmetry in the magnetosphere‐ionosphere coupling process associated with the flow.