TRANSITION TO TURBULENCE IN SOLAR SURGES

Transition to turbulence in magnetohydrodynamic tearing jets has been invoked as a mechanism underlying some of the complex behavior observe d in solar surges, including deceleration of the upflowing plasma and temporal correlations with types I and III radio bursts. In this paper we investigate a possible mechanism for this transition: three-dimens ional secondary instabilities on two-dimensional saturated states. We find through linear analysis that these MHD configurations-in particul ar, the tearing jet-are secondarily unstable, with the dominant energy transfer from the one-dimensional field into the 3-dimensional fields . Using nonlinear simulations, we also investigate the system evolutio n after the secondary modes attain finite amplitude. When the tearing jet transitions to turbulence, the total kinetic energy drops rapidly corresponding to the deceleration of the jet. The electric field grows rapidly as the primary mode saturates and the three-dimensional secon dary mode develops, and then decays quickly as the tearing jet becomes turbulent, providing a possible explanation for the finite duration o f the associated meter-wave bursts. The electric field decays as the m agnetic and velocity fields both decay. The system is dominated at lat e times by spanwise modes, which strongly resemble the magnetic field- aligned filamentary flows characteristic of many surges.