Numerical simulation of the three-dimensional structure
and dynamics of the non-magnetic solar chromosphere
Three-dimensional numerical simulations with
CO5BOLD, a new
radiation hydrodynamics code, result in a dynamic, thermally
bifurcated model of the non-magnetic chromosphere of the quiet Sun.
The 3-D model includes the middle and low chromosphere, the
photosphere, and the top of the convection zone, where acoustic waves
are excited by convective motions. While the waves propagate upwards,
they steepen into shocks, dissipate, and deposit their mechanical
energy as heat in the chromosphere.
Our numerical simulations show for the first time a complex 3-D
structure of the chromospheric layers, formed by the interaction of
Horizontal temperature cross-sections of the model chromosphere
exhibit a network of hot filaments and enclosed cool regions.
The horizontal pattern evolves on short time-scales of the order of typically
20 - 25 seconds, and has spatial scales comparable to those of the
The resulting thermal bifurcation, i.e., the co-existence of cold and
hot regions, provides temperatures high enough to produce the observed
chromospheric UV emission and -- at the same time -- temperatures cold
enough to allow the formation of molecules (e.g., carbon monoxide).
Our 3-D model corroborates the finding by Carlsson & Stein (1994)
that the chromospheric temperature rise of semi-empirical models does
not necessarily imply an increase in the average gas temperature but
can be explained by the presence of substantial spatial and temporal
(The abstract also appeared in
COOLNEWS, issue 94, December 2003.)
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