(Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, 79104 Freiburg, Germany)
On the fine structure of the solar Ca II K atmosphere
We investigate the evolutionary, dynamical, and morphological properties of the
internetwork and network fine structure of the quiet sun at disk centre.
The analysis is based on a ~6 h time sequence of
narrow-band filtergrams centred on the inner-wing
Ca II K2v reversal at 393.3 nm.
To examine the temporal evolution of network and internetwork areas separately
we employ a double-Gaussian decomposition of the mean intensity distribution.
An autocorrelation analysis is performed to determine the respective characteristic time scales.
The results for the internetwork are related to predictions derived from
numerical simulations of the quiet sun. In order to analyse statistical
properties of the fine structure we apply image segmentation techniques.
The average evolutionary time scale of the internetwork in our observations
is 52 sec, that of the network ranges from 6 min to 68 min with an average of 44 min.
Internetwork grains show a tendency to appear on a mesh-like pattern on a spatial scale
of 4-5 arcsec. We relate this pattern to the existence of photospheric downdrafts
as predicted by convection simulations. The p-mode ridges in the k-nu-diagram
extend beyond the acoustic cut-off frequency of ~5 mHz to at least 7.5 mHz,
at the high harmonic degrees we observe.
The image segmentation shows that typical sizes of network and internetwork grains
are very similar and makes clear that their filling factor is highly dependent on
spatial and spectral resolution, and the chosen intensity threshold.
Download the article as
PDF (215 kB)
Back to index.