Numerical Simulations of Solar Chromospheric Jets Associated with Emerging Flux

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 outflow 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, this 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 the 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. In the process, the magnetic energy released by magnetic reconnection is efficiently converted into the kinetic energy of jets. This is an MHD effect that has not been discussed before.