Hammer, R.

Contact Email: hammer@kis.uni-freiburg.de
Institute: Kiepenheuer-Institut fuer Sonnenphysik
First Coauthor: A. Nesis
Institute: Kiepenheuer-Institut fuer Sonnenphysik
Subject Area: The Sun
Waveband: Optical
Technique: Computational Astrophysics
Presentation: Poster Display
Title: What Controls Spicule Velocities and Heights?
Abstract: Numerous mechanisms have been suggested to drive spicules. Many of them, however, need a careful fine-tuning of free parameters in order to achieve the basic characteristics, i.e. velocity and height, of observed spicules. There might be general physical mechanisms that control these properties. We show that whenever upper chromospheric plasma is exposed to a significantly nonhydrostatic pressure gradient, it will start moving upward at the observed speeds. The plasma can well reach the observed height range, in particular if it receives some net chromospheric heating during the rising phase. Therefore, such a hydrodynamic mechanism might help other (magnetic) mechanisms to control the basic properties of spicules. It might even be the main driving agent. We suggest therefore to consider a new class of spicule driving mechanisms, in which the plasma is not (or not only) accelerated by wave or magnetic forces from below, but rather by the generation of a low pressure region above the chromosphere. Such a situation could arise e.g. due to an instability in magnetic loops or as a result of the reconfiguration of open field lines.