Intercomparison of spectral databases using downwelling spectra in the shortwave part of the water vapour rotational band

Ground-based Fourier Transform Spectrometer observations in the infrared, acquired during the Italian phase of the EAQUATE campaign, have been considered in this study and compared to calculations. Synthetic spectral radiances have been obtained using the 2000 and 2004 releases and the 2006 upgrade of HITRAN spectral databases. It has been found that synthetic radiance computations fit the data quite well, even though the goodness of the fit depends on the spectral database. Differences in the spectral residual behaviour appear to be mostly localized in the long-wave side of the Earth emission spectrum, i.e. in the spectral region 520–610 cm−1, which is dominated by the water vapour rotational absorption band. In this range, computation performed with the latest updates provides almost the same results as those of HITRAN2000, while HITRAN2004 shows a mixed behaviour—better than the first two in a large region of the spectral range, but worse at very few specific wave numbers. Overall, HITRAN2006 yields the highest consistency with the observations. No sensitive differences appear at higher wave numbers.