5. Discussion and conclusion
The height dependencies of the model correlations will change if we use another method to calculate mean correlation coefficients: we may collect data belonging to each horizontal level over a whole time series of our models and then calculate correlations between these data. But the height dependencies of the new correlations differ from those discussed in this paper not more than by 20-30 km and this does not change significantly our main conclusions.
From our simulated spectral observations we do not detect the sharp drop of correlation between spatial fluctuations of vertical velocities in the low and in the middle photosphere as it was reported by Karpinsky (1990). An explanation can be that our models are obviously more laminar than the real solar photosphere. However, this conclusion of Karpinsky was not confirmed later.
Our results with high correlation between horizontal velocities in the model photosphere are also in disagreement with a study of Nesis et al. (1988), where they found, based on observations, that horizontal velocities are coherent only in the low photosphere. We do not exclude that our model result could be influenced by the 2-D cartesian approach, close to laminar treatment of the medium, and spatially limited computational domain.
In spite of this the correlations derived from observations and from simulations of several Fe I and Fe II lines are in good agreement. Therefore, summarizing our results we may conclude that:
Schematically, the structure of the model photosphere can be presented as the following:
Finally we point out that multidimensional selfconsistent model atmospheres can be successfully used to test possible criteria in estimation of "line formation depths". Although our results show that the scale seems to be better suited for diagnostic purpose than the line formation depths found with the depression contribution functions we suggest to test also physically more adequate methods using the conception of the response functions.
© European Southern Observatory (ESO) 2000
Online publication: December 5, 2000