A rebound shock mechanism for solar fibrils
Flows along a rigid solar magnetic flux tube which is horizontal over a substantial portion of its length are numerically investigated. A single, quasi-impulsive force near the base of the first vertical segment drives a series of upward propagating rebound shocks on the flux tube. When the horizontal segment is in the corona, the shocks raise the transition region onto the horizontal segment and eventually onto the coronal vertical segment. The material behind the displaced transition region resembles a fibril on the horizontal segment, and a short spicule on the second vertical segment. A full-sized spicule does not develop. The resulting density of the material on the horizontal segment is 10 to the -14th g/cu cm, which is consistent with the observed densities in fibrils. When the horizontal segment is in the chromosphere, the motions and densities induced on the horizontal segment do not resemble those of observed fibrils, and a full-sized spicule again does not develop.