Are spicules driven by oscillations?

The formation of spicules on the solar surface is poorly understood. In the present investigation, we propose a mechanism that provides an explanation for this phenomenon. The squeeze of the enhanced downflow region in the intergranular lanes by oscillation results in an initial narrow, high-speed upward flow with a velocity on the order of several kilometers per second and a width on the order of 10 km. The underlying physics principle is the same as in the design of an anti-tank weapon, called a “shaped charge”. The life of a spicule is divided into two stages. The first stage is mechanical driving by the pressure gradient at its base; the second stage is electromagnetic driving. Dynamo action in the early lifetime of a spicule plays an important role in the transfer of mechanical energy to magnetic energy. The subsequent Fermi acceleration is responsible for the energy transfer from magnetic energy to thermal energy and kinetic energy. Depending on the strength of the ambient magnetic field, the formation of type I spicules (strong case) and type II spicules (weak case) can be naturally explained in this frame setting, which is one of the merits of our proposed mechanism. The variation in temperature along the height is consistent with prior observation-based models.