Chromosphere of the quiet sun: statistical study of emission line profiles, atmospheric models and dynamical properties

The magnetic structure of the calm solar atmosphere (magnetic network and inter-network) constitutes an essential element for the study of the heating of the chromosphere and the corona by acoustic and magnetohydrodynamic waves. The UV emission profiles, observed by the French spectrometer of the OSO-8 satellite, are the basis of the statistical study carried out in six resonance lines formed at different altitudes. The Lyman-alpha and Lyman-beta lines of hydrogen, h and k of calcium (once ionized), and h and k of magnesium (once ionized), were recorded simultaneously, at the center of the solar disk. From this database corresponding to one year of observations, the correlations between the parameters of the same line or of two different lines were established. The average profiles of the six observed lines were obtained for the calm sun, the network and the inter-network, and are compared to the profiles calculated with the Gouttebroze out-LTE (Local Thermodynamic Equilibrium) radiation transfer code. Various atmospheric models have been used (VAL, FAL). The differences between theoretical profiles and observed profiles led to construct two new models which give encouraging results. Dynamic properties of the network and the inter-network were obtained from a sequence of 83 minute observations made at the NSO/SP, simultaneously in two lines formed at different altitudes: the k line of calcium (once ionized) and the line at 1083 nm of neutral helium. After processing the spectral images, the study of the Doppler speed over the whole sequence indicates the presence of oscillations of five minute periods in the network and of three minute periods in the inter-network. New results concerning the lifespan of wave trains have been provided thanks to a time / frequency analysis of the Doppler speed by the wavelet transform method