  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. We solve two-dimensional time-dependent magnetohydrodynamic equations
numerically to find spatial and temporal dynamics of spicules. 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 raising and falling off
plasma portions resembles the time sequence of single and double (sometimes
even triple) spicules, which is consistent with observational findings. 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.
