Speaker
Elena Khomenko
Description
Solar atmospheric plasma is not in a neutral state nor in a fully ionized state. The
influence of this plasma state on the dynamics becomes currently the focus of many
investigations. Even though the collisions are strong in the atmosphere of the Sun,
it can be expected that ions may become magnetized at some height between the
photosphere and the chromosphere, depending on the strength of the magnetic field.
This may cause partial decoupling of the neutral and charged species, producing
differences in their velocities since different forces are acting on them. Therefore,
in principle, the velocities measured from spectral lines of neutral and ionized
species may slightly differ. In this contribution we will present the attempts to
observationally measure the possible decoupling between the ionized and neutral
species. We will describe the results of two specially dedicated observational
campaign. In one case, we targeted Evershed flow in sunspots using five pairs of
ionized and neutral iron lines. In the other case, we targeted prominence plasma
using ionized calcium line and neutral helium lines. In both cases we observe that
velocities of ions and neutrals originating from the same volume of plasma are very
similar. However, important differences have also been detected. In sunspots we find
measurable differences in the radial component of the flow. The flow measured from
the neutral iron lines has an amplitude that is a few hundred meters per second
larger than that of the ionized iron lines lines. In prominences, we find
short-lived transients, coherent in space and time, where ion and neutral velocities
are different. These transients are sometimes associated with strong spatial or
temporal gradients in the individual velocities of calcium ions and helium atoms.
