A metatheory about spicules

Spicules dominate the solar coronal mass balance. Their driving mechanisms have not yet been identified, although numerous theories have been put forward that appear to be able to explain the most basic spicule properties, i.e. their velocities and heights. We point out that some observational facts, in particular the spicular group behavior and bipolar flows, axe hardly consistent with a unique driving mechanism. Thus it may well be that different driving mechanisms axe operating at different times and places on the Sun, depending on the dynamics and magnetic topology. The basic reason why all these mechanisms produce spicules with the same observed speed must be sought in the equipartition between kinetic energy density and specific enthalpy, and also the magnetic energy density in the case of magnetic mechanisms. Equipartition between enthalpy and kinetic energy is a natural consequence of all mechanisms that axe based on a steep pressure gradient in the chromosphere, which results from either a pressure increase in the lower, or a decrease in the upper atmosphere.