Transition region and coronal loops heated by turbulence

In a recent paper, we proposed that Alfvén waves damped by a fully developed turbulent cascade is responsible to produce hot coronal loops with plasma flows (Li and Habbal, 2003). This paper is an extension of that work. Two fluid dynamic models of long-lived coronal loops with various loop lengths are presented. It is assumed that the nonthermal motions inferred from spectral line observations in the transition region are due to Alfvén waves. These waves originate below the chromosphere and are responsible for the coronal heating when they are dissipated by a turbulent cascade. The cascade process transfers energy from large scales to high frequency small scales where the wave energy can be readily absorbed by the proton gas. The Coulomb coupling between protons and electrons subsequently heats the electron gas. The models reproduce electron densities of 1 - 4×10 ⁹ cm ^-3, in the range inferred from observations. The mechanism is able to produce coronal loops with various lengths. Given the same physical and heating parameters, it is found that small loops tend to have slow plasma flow, low temperatures and high densities in the main part of a coronal loop. Steady state plasma flow speed as fast as 40km/s is easily obtained in large loops.