Dynamic current injection into magnetic loops in active regions II. A 3D magnetodynamic model for loop flares

We have studied propagation along magnetic flux tubes in the active-region corona of large-amplitude torsional Alfven wave packets; (TAWP's) coming up from a subphotospheric convection zone. TAWP's can serve to transfer magne tic energy from the high-beta (beta = P-g/P-m) subphotospheric region to th e low-beta coronal region. They dump part (or all) of their energy in the l ow-beta coronal region, which may result in very high temperature-plasma ob served in X-rays (and in high energy particles). The supply of TAWPs from t he photosphere considered to be inefficient because the Alfven velocity in the photosphere is small, turns out to be sufficiently effective for large- amplitude TAWP's. This is due to the magnetic buoyancy acting on the magnet ic twist packet and to the non-linear effect of squeezing out the gas from the twisted part of loops when it comes up near the photosphere. Both of th ese effects enhance the speed of emergence of the twist. We propose that lo op flares may be due to the transport of energy and mass by torsional Alfve n waves. They may be the result of energy conversion of the magnetic twists and the kinetic energy of the accelerated hypersonic Hows into thermal ene rgy when two such TAWP's collide high in a coronal loop. In order for such a collision of TAWP's to occur, a TAWP is injected from one footpoint of a loop whilst another TAWP. from the other footpoint, is still propagating al ong the loop. The collision of these two TAWP's at a high part of the loop explains the creation of a hyperhot region. The acceleration of high-energy particles is also explained as being due to the Fermi-I process between th e approaching two hypersonic magnetic shocks.