High-resolution photography of the solar chromosphere

High-resolution filtergrams of an active region loop taken at seven wavelengths in Hα have been used to derive the contrast at eleven locations along its length as a function of wavelength. With an appropriate choice of parameters, theoretical curves calculated on the basis of the ‘cloud” model give a reasonable fit to the observed contrast profiles. The inferred line-of-sight components of the mass velocity range from 27 km s^?1 upward to 78 km s^?1 downward. However, more accurate profiles and a more rigorous theory are needed to confirm the validity of this application of the cloud model.