The Structure of the Solar Chromosphere: I. Identification of Spicules on the Disk

Spicules have been studied in the H α line with ( a ) a 1/8 Å tunable filter, and ( b ) a 3/4 Å filter equipped with a beam splitter yielding simultaneous photographs in opposite wings. Spicules have been traced from outside the solar limb on to the chromospheric disk just inside the limb, where they appear as bright emission features. On the disk, they appear as mottles which are bright at all positions across the line profile. The well-known dark mottles, although merging to form the general chromosphere at the limb, do not extend beyond as spicules. However, there is a close association between the dark and bright mottles, the latter being found in the central parts of the well-known chains of the chromospheric network or of clusters of dark mottles. A three-dimensional model of some of these structures is described.