c © ESO 2010 Astronomy &Astrophysics

Context. We study the upward propagation of a localized velocity pulse that is initially launched below the transition region within the solar atmosphere. The pulse quickly steepens into a shock, which may lead to the formation of spicules. Aims. We aim to explore the spicule formation scenario in the framework of the rebound shock model. Methods. We solve two-dimensional time-dependent magnetohydrodynamic equations numerically to find spatial and temporal dy-namics of spicules. Results. The numerical simulations show that the strong initial pulse may lead to the quasi periodic rising of chromospheric material into the lower corona in the form of spicules. The periodicity results from the nonlinear wake that is formed behind the pulse in the stratified atmosphere. The superposition of rising and falling off plasma portions resembles the time sequence of single and double (sometimes even triple) spicules, which is consistent with observational findings. Conclusions. The two-dimensional rebound shock model may explain the observed speed, width, and heights of type I spicules, as well as observed multi-structural and bi-directional flows. The model also predicts the appearance of spicules with 3–5 min period due to the consecutive shocks. Key words. magnetohydrodynamics (MHD) – instabilities – Sun: atmosphere 1