On the motions of chromospheric fine-structure in a weak plage

Abstract

Motions in an old center of activity have been studied at the limb with the use of timeresolved Hα spectra. The observations were made at intervals of 5 seconds over a period of 3/4 hour of good seeing at Sacramento Peak Observatory.

Objects in this region have larger line-of-sight velocities than have been reported for spicules in quiet regions. Velocities as high as 70 km/sec were observed; seventeen percent of a sample of 200 instantaneous velocities exceed 30 km/sec.

The line-of-sight velocities of 20 objects were measured as a function of time. For 5 of these, transverse velocity components could also be estimated. A single pattern, such as the simple rise without fall reported by Mouradian, does not exist. The motion is often quite complex, involving lateral expansion, shear and occasionally splitting. Reversal of sign of the velocity is not uncommon.