Hα fine structure and the chromospheric field

The physical characteristics of the H structures previously defined as fibrils and threads are studied. The interpretation of the fibrils as ends of flux tubes is useful in tracing the behavior of the transverse field component over the solar surface.The observed properties of fibrils and threads are consistent with the hypothesis that they are produced by a shock wave mechanism similar to that advanced by Parker to explain spicules. It is suggested that the undisturbed magnetic field in the chromosphere of an active region is confined to a thin sheath, while the field of the quiet regions extends into the corona.