A 50 min time series of one-dimensional slit-spectrograms , taken in quiet sun at disk centre , observed at the German Vacuum Tower Telescope ( Observatorio del Teide ) , was used to study the global and spatial variations of different line parameters .
In order to determine the vertical structure of the photosphere two lines with well separated formation heights have been considered .
The data have been filtered of p-modes to isolate the pure convective phenomenon .
From our studies of global correlation coefficients and coherence and phase shift analyses between the several line parameters , the following results can be reported .
The convective velocity pattern preserves structures larger than 1 \aas@@fstack { \prime \prime } 0 up to the highest layers of the photosphere ( \sim 435 km ) .
However , at these layers , in the intensity pattern only structures larger than 2 \aas@@fstack { \prime \prime } 0 are still connected with those at the continuum level although showing inverted brightness contrast .
This confirms an inversion of temperature that we have found at a height of \sim 140 km .
A possible evidence of gravity waves superimposed to the convective motions is derived from the phase shift analysis .
We interprete the behaviour of the full width at half maximum and the equivalent width as a function of the distance to the granular borders , as a consequence of enhanced turbulence and/or strong velocity gradients in the intergranular lanes .