Time series of high resolution photospheric spectra in a quiet region of the Sun. I. Analysis of global and spatial variations of line parameters

TL;DR

This study analyzes high-resolution solar photospheric spectra to understand the spatial and vertical variations of line parameters, revealing convective structures, temperature inversion, and potential gravity wave signatures in the quiet Sun.

Contribution

It provides detailed analysis of line parameter variations with height and spatial scale, highlighting the persistence of convective patterns and temperature inversion at specific layers.

Findings

Convective velocity structures persist up to ~435 km height.

Temperature inversion occurs at approximately 140 km height.

Evidence suggests gravity waves may be present in the photosphere.

Abstract

A 50 min time series of one-dimensional slit-spectrograms, taken in quiet sun at disk center, 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 analyzes between the several line parameters, the following results can be reported. The convective velocity pattern preserves structures larger than 1.0" up to the highest layers of the photosphere (~ 435 km). However, at these layers, in the intensity pattern only structures larger than 2.0" 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 ~140 km. A possible evidence of gravity waves superimposed to the convective motions is derived from the phase shift analysis. We interpret the behavior 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.