The authors have revised their analysis of the far-infrared Fourier-transform spectrometer measurements of the 1-0 and 3-2 PH 3 transition in Saturn's disk. This reanalysis was prompted by the detection of a software error in the radiative transfer program that was used to create synthetic spectra to match the observations. An error in a recent revision of the software had inadvertently reduced values of optical thickness along a path. Thus, the optical thickness of PH 3 lines were systematically low and required more PH 3 to match the observations than was necessary; the H 2 continuum values were not influenced by this error.
As shown in the revision of Fig. 1, the revised best fit is consistent with a PH 3 mixing ratio at 645 mbar of 7.4 × 10 -6 that drops linearly in log (pressure) vs log (mixing ratio) to a value at 150 mbar of 4.3 × 10 -7 at 150 mbar pressure. The mixing ratio can be expressed as a function of pressure, p in bars, as 1.75 × 10 -5 p 1.95 . As in the original model, the quality of the fit is not diminished if either (1) the mixing ratio drops to zero for pressures less than 150 mbar or (2) the mixing ratio remains constant for pressures greater than 630 mbar. A model with a constant PH 3 mixing ratio with depth for pressures greater than 630 mbar shows a slightly better fit to the data than extrapolating the steep increase that holds at lower pressures. The spectra of these new models are negligibly different from the corresponding original figure.
The revised models still show that the PH 3 vertical distribution derived by Courtin et al. (1984) is not consistent with our data, showing a very prominent emission feature not observed in the 3-2 line. Our PH 3 vertical distribution is now closer to the one used to FIG. 1. Vertical distributions of PH 3 . The standard model is shown with a solid line, with the region to which our data are sensitive illustrated with a thicker line. The vertical distribution of PH 3 derived by Noll and Larson (1990) is given by the dashed line. The temperature profile is given by the dotted line.