Calculated k distribution coefficients for hydrogen‐ and self‐broadened methane in the range 2000–9500 cm⁻¹ from exponential sum fitting to band‐modelled spectra

Abstract

The spectral band data derived by Strong et al. [ 1993] for laboratory-measured transmission spectra of hydrogen-broadened methane at 10 cm -t resolution have been fitted with k coefficients over a wide range of pressures and temperatures representing those likely to be encountered in the atmosphere of Jupiter. The mean fitting error is found to be only 2.0x10 -3 in transmission. These data are essential for the scattering calculations likely to be necessary for analysis of the data from the Near Infrared Mapping Spectrometer aboard the NASA Galileo spacecraft. The new data have significant advantages over those previously derived by Baines et al. [ 1993] in that they cover a wider spectral range, are applicable to longer paths, and also apply to the hydrogen-broadened case, which is the dominant broadening mechanism in this atmosphere. A similar table has also been calculated for the self-broadening case for comparison.

Structure of the Jovian Stratosphere at the Galileo Probe Entry Site

“…The transmission found using the Baines et al (1993) coefficients is significantly less than that calculated with the Irwin et al (1996) coefficients and the heating rate is significantly higher in the 0.02-3 mbar region. However, it is not clear that the Baines et al (1993) coefficients are more accurate than those of Irwin et al (1993) for this region of the jovian atmosphere.…”

“…Figures 8 and 9 show transmission spectra and heating rates calculated using the Irwin et al (1996) and Baines et al (1993) coefficients. The transmission found using the Baines et al (1993) coefficients is significantly less than that calculated with the Irwin et al (1996) coefficients and the heating rate is significantly higher in the 0.02-3 mbar region.…”

“…The Irwin et al (1996) coefficients have the advantage of wider wavelength coverage and of being based on laboratory conditions in which broadening was primarily by H 2 . However, the Strong et al (1993) and Irwin et al (1996) investigations were directed primarily toward the troposphere and, in general, concern higher pressures and temperatures than those that pertain to the jovian stratosphere.…”

“…The Irwin et al (1996) coefficients have the advantage of wider wavelength coverage and of being based on laboratory conditions in which broadening was primarily by H 2 . However, the Strong et al (1993) and Irwin et al (1996) investigations were directed primarily toward the troposphere and, in general, concern higher pressures and temperatures than those that pertain to the jovian stratosphere. The principle advantage of the Baines et al (1993) coefficients is their use of the Giver et al (1990) laboratory measurements, which extend to lower temperatures than do Strong et al's (1993).…”

“…There are a number of sources for these coefficients. Recently, Irwin et al (1996) published k-coefficients for the CH 4 bands that are based on Strong et al's (1993) laboratory measurements of CH 4 transmission spectra. Also, Baines et al (1993) has derived k-coefficients, over a more limited spectral region, from the laboratory measurements of Giver et al (1990).…”