A Statistical Study of the Spatial Scales of the Terrestrial Bow Shock

The spatial scales of the shock transition are directly related to the physical processes that lead to shock formation. In addition they determine the mechanism of the interaction between the incoming plasma particles and the macroscopic fields within the shock front. The multipoint data used in the present study enable the separation spatial and temporal variations and hence to identify spatial scales. The identification of spatial scales has been performed for shocks observed by the Cluster and THEMIS spacecraft. The statistical dependences of the electric field and magnetic ramp scales versus shock parameter (Mach number, angle between the shock normal and the upstream magnetic field etc) indicate that the dispersion of the high amplitude fast magnetosonic waves contributes to the formation of the magnetic ramp. This implies nonstationarity of the shock front if the Mach Number exceeds the whistler critical Mach number. The consequencies for the dynamics of electrons within the magnetic ramp are analysed.