Coronal heating and the vertical temperature structure of the quiet corona

The radial variation of temperature in the inner corona is examined using long-exposure Yohkoh images of two regions of diffuse (quiet) corona. The results indicate a steady radial increase of temperature for both regions, out to 0.7 and 0.95 solar radii above the limb. We find that the filter-ratio data for the two regions is well fitted in each case by integration over the line of sight of a spherically symmetric model atmosphere in hydrostatic equilibrium and with a temperature profile due to a conserved inward heat flux. An Abel inversion process is also applied to the data, and this gives results consistent with the spherically symmetric, conserved-heat flux model. These results imply that the nonthermal energy responsible for heating these regions of the quiet corona is being deposited beyond the observed range of heights. However, the diffuse regions we examined are believed to be partly closed-field regions, and so, the radial models require careful interpretation. We discuss the implications for coronal heating in these regions.