Mechanisms of the plasma upflow formation in the solar atmosphere. The sketch shows the magnetic field topology of the active region core and the upflow region (left side) and the description of the plasma flow in each region that corresponds to the blue (upflow) and red (downflow) arrows on the left side. The active region core is built with the hot coronal loop (yellow). The open magnetic field topology is characteristic for the upflow region (grey). In the chromosphere exists numerous small-scale loops (yellow). The numbers describe the processes responsible for the upflow generation. (1) The reconnection between the closed loop and open magnetic field lines (orange X) in the upper transition region or lower corona. Owing to reconnection, plasma is injected towards the corona and chromosphere. The magnetic field increases towards the chromosphere and can decelerate the plasma flow in this direction. (2) The reconnection between the small-scale chromospheric loop and open magnetic field lines (orange X). Owing to reconnection, plasma is injected towards the lower chromosphere and the transition region. The expanding open magnetic fields lines allow the plasma propagate further to the corona. (3) The open magnetic field structure allows plasma to escape from the chromosphere through the transition region to the solar corona. This process is accelerated by waves propagated in the lower solar atmosphere.