Cluster observations of reconnection due to the Kelvin-Helmholtz instability at the dawnside magnetospheric flank

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 similar to 2-3 min bipolar variations for 1 h when the IMF had a small positive b(z)-component and a Parker-spiral orientation in the x, y-plane. Brief similar to 33 s intervals with excellent deHoffman Teller frames were observed satisfying the Walen relation. Detailed comparisons with 2D MHD simulations indicate that Cluster encountered rotational discontinuities generated by Kelvin-Helmholtz instability. We estimate a wave length of similar to 6 R(E) and a wave vector with a significant z-component.