Abstract. On 3 July 2001, the four Cluster satellites traversed along the dawnside magnetospheric flank and observed large variations in all plasma parameters. The estimated magnetopause boundary normals were oscillating in the z-direction and the normal component of the magnetic field showed systematic 2–3 min bipolar variations for 1 h when the IMF had a small positive bz-component and a Parker-spiral orientation in the x,y-plane. Brief 33 s intervals with excellent deHoffman Teller frames were observed satisfying the Walén relation. Detailed comparisons with 2-D MHD simulations indicate that Cluster encountered rotational discontinuities generated by Kelvin-Helmholtz instability. We estimate a wave length of 6 RE and a wave vector with a significant z-component.
