Coronal Heating: Parker Model or Turbulence, or Both?

Abstract:

In our previous paper [Ng et al., Astrophys. J. 747, 109, 2012], we have concluded that the Parker model of coronal heating can provide enough heating, independent of Lundquist number, for the quasi-equilibrium case with the coronal loop length L much shorter than V_At_c, the distance travelled by Alfven waves during one correlation time of random photospheric motions. We have now generalized our simulations with cases to longer L. We will present most recent results from a series of three-dimensional simulations based on the equations of reduced magnetohydrodynamics for the time-averaged energy dissipation rate <W> as a function of L. In the limit of L >> V_At_c, we show that <W> is given by the photospheric Poynting flux required to launch Alfven waves. In the intermediate range of L ~ V_At_c, <W> is well described by a scaling based on the Kolmogorov turbulence energy cascade, rather than the Iroshnikov-Kraichnan cascade. For the whole range of L we considered, we will show that <W> can be modeled by combining the Parker heating and the Alfven wave launching power. This work is supported by a NSF grant AGS-0962477.