  We studied the acceleration mechanisms of chromospheric jets associated with
emerging flux using a two dimensional magnetohydrodynamic (MHD) simulation. We
found that slow mode shock waves generated by magnetic reconnection in the
chromosphere and the photosphere play key roles in the acceleration mechanisms
of chromospheric jets. An important parameter is the height of magnetic
reconnection. When magnetic reconnection takes place near the photosphere, the
reconnection out- flow collides with the region where the plasma beta is much
larger than unity. Then the plasma moves along a magnetic field. This motion
generates a slow mode wave. The slow mode wave develops to a strong slow shock
as it propagates upward. When the slow shock crosses the transition region, the
transition region is lifted up. As a result, we obtain a chromospheric jet as
the lifted transition region. When magnetic reconnection takes place in the
upper chromosphere, the chromospheric plasma is accelerated due to the
combination of the Lorentz force and the whip-like motion of magnetic field. We
found that the chromospheric plasma is further accelerated through the
interaction between the transition region (steep density gradient) and a slow
shock emanating from the reconnection point. This is an MHD effect which has
not been discussed before.
