A MODEL OF THE SOLAR CHROMOSPHERE-CORONA TRANSITION REGION BASED ON CLASSICAL THERMAL CONDUCTION

We assert that a hot corona cooled by inward thermal conduction very likely results in a transition region whose isotherms follow a highly roughened surface. Assuming a checkerboard of cool peaks and hot valleys in surfaces of constant temperature and using the observed emission measure at T = 6 × 104 K, we find H/λ, the ratio of the mean height of the cool peaks, to the mean separation of peaks and valleys, to have a value of 160. By allowing nearly all of the parallel conduction flux of 106 ergs cm-2 s-1 at T= 106 K in the hot valleys to flow across magnetic field lines into the cool peaks, we find a predicted emission measure in very good agreement with the low-temperature branch of the observed emission measure, including the Lyγ region. This purely conductive model has the advantages of explaining both the observed emission measure curve and the wide vertical extent of the transition region at the limb without introducing ad hoc secondary heat sources.