Evolution of the Elsässer variables at the CME flank. The spatio-temporal evolution of the Elsässer variables for the non-radial directions in the frame of reference of the shock (x = 0) is presented. The quantities are shown for a viewing angle of 160°, and an Alfvénic fluctuation frequency of 3 mHz. The x-axis denotes the shock neighbourhood in units of R_⊙; positive values indicate the solar wind and negative values indicate the region downstream of the shock.