1996A&A...310...49C

We estimate the properties of clouds that form as a result of the interaction of the surface of a disc embedded in a supersonic outflow and heated by external irradiation. We find two regions where short-lived clouds are injected into the outflow and accelerated by ram pressure. We identify these with a broad line region and an intermediate line region. We compute the line strengths and profiles from a model of the cloud dynamics and compare the results with the observations of the nearest Seyfert galaxy NGC 4151, which, in its various luminosity states, has provided a large amount of emission line data. We show that the model parameters for this galaxy are constrained by just the C IV λ1549 line profile in the high luminosity state of the nucleus. We review briefly some of the data on broad line ratios, profiles, profile variations and transfer functions and show how much (if not all) of this data can be accounted for in the model. We also indicate how the X-ray data can be fitted into this picture.