A theoretical model of a coronal hole.

A shock-heated coronal-hole model is obtained by solving four coupled differential equations for mass conservation, energy conservation, momentum conservation, and shock-wave propagation in one-dimensional spherical coordinates. Thermal conduction and radiative losses are taken into account, and boundary conditions are determined from studies of the solar corona and chromosphere. EUV emission-line intensities and radio brightness temperatures are calculated and compared with a wide range of observations, including OSO 4 coronal-hole observations and Skylab spectroheliograms. Difficulties in reconciling the low coronal densities inferred from radio observations with the high densities expected on the basis of EUV data are discussed. The model is shown to explain satisfactorily a wide variety of observations with a minimum of adjustable parameters.