Turbulent thermal conduction in the solar transition region

Emission measures E(T) derived from EUV observations of the lower solar transition region indicate that there is far more material in that temperature range than can be explained within the steady single flux-tube scenario if the classical energy transfer and loss mechanisms are adopted. This suggests that some mechanism may be operating which reduces the temperature gradient. The inclusion of a turbulent thermal conductivity kappa(T) = phi rho c(p)ul in a one-dimensional model is investigated, where u is the rms microvelocity in one direction, l is the mixing length, and phi is a constant of order unity. If it is assumed that that l is proportional to T exp-alpha, it is shown that near-perfect agreement with the observed emission measures is obtained for alpha = 3/2, both as regards the slope d log E/d log T equal to about -3 in the LTR, and the upturn at the top of this range. 27 refs