Study of the chromospheric fine structure in Hα

The physical parameters, derived from fitting a modified cloud model to the contrast profiles of chromospheric mottles near the limb, indicate that both bright and dark mottles should be seen as spicules beyond the limb. The bright mottles are identified with spicules which have broad spectral line profiles, large Doppler shifts, and appear faintly at great heights. The dark mottles are identified with spicules which are very bright at great heights, but show rather small Doppler shifts. Brightness histograms of chromospheric objects at various wavelengths were obtained in the second part of this paper. Observations of the contrast profiles of the chromospheric mottles and other objects were used to explain the appearance of peaks in the histograms with some success. It also appears that the physical conditions in each type of object have characteristic values