Reduced Thermal Conduction in Solar Coronal Loops

Thermal conduction plays an important role in the energy balance of the solar coronal plasma. In this paper, we present a new method for deriving observational constraints on the density–temperature relationship for coronal loops from the differential emission measure distributions of active regions and apply the method to measurements obtained with the Extreme-Ultraviolet Imaging Spectrometer on Hinode. Our focus is on coronal loops in the cores of active regions. We show that standard loop models do not reproduce the observed loop-top densities when the variations of cross-sectional area along the loop are taken into account. Nonstandard loop models with reduced thermal conductivity (compared to Spitzer’s law) are presented. The modeling results are compared with published measurements of loop parameters obtained with the Soft X-ray Telescope on Yohkoh. We conclude that models with reduced thermal conductivity are better able to reproduce the observed loop-top densities.