Height variation of the solar granulation

We analyze spectral scans of narrow-band images across the Na D-2 line. They were obtained from disc centre of the Sun with our Fabry-Perot interferometer (FPI) in the Vacuum Tower Telescope at the Observatorio del Teide. The FPI was set to a bandwidth of 200 m Angstrom FWHM and the spectral stepwidth was 100 m Angstrom. Our aim is to study the variation of the granulation pattern with height in the atmosphere. To achieve high spatial resolution the simultaneously taken broad-band images are restored with speckle methods. With the knowledge of these reconstructed images we were also able to restore the narrowband images. The formation heights are found from temperature response functions RFT. In the wings of NaD2, the response functions for different wavelengths exhibit a substantial overlap in atmospheric heights. Therefore we use linear combinations which allow a better height discrimination. Applying the same combinations to the D-2 images we can visualize the height variation of the granular pattern. The granular intensity fluctuations are a matter of the deep photosphere alone. They disappear at heights of about 100 km (above tau(5000) = 1).