CLOUD MODEL WITH VARIABLE SOURCE FUNCTION FOR SOLAR H-ALPHA STRUCTURES

The ''cloud model'' used to derive the physical parameters of solar ch romospheric features is extended to the cases of non-constant source f unction and of velocity gradients. This model assumes a given relation ship between the source function and the opacity of the cloud which is derived from non-LTE modelling. An algorithm using 4 points of the H- alpha profile is proposed to derive the optical thickness, the line-of -sight velocity and the dopplerwidth. The results are compared with a 5-points inversion which does not use the given relationship between s ource function and opacity. Effects of the uncertainty about the radia tion coming from the underlying chromosphere, as well as effects of da ta noise, are discussed. The inversion method is illustrated by some e xamples of observed profiles obtained with the MSDP spectrograph of th e VTT telescope (Teide Observatory).