Continuous absorption of water vapor and a problem of the absorption enhancement in the humid atmosphere

Abstract

Our recent studies of the nonlinear continuum absorption of the pure water vapor have been extended on a case of the air broadening. The nonlinear absorption dependence has been derived for inhomogeneous optical mediums. The absorption of water within the air atmosphere and the Rayleigh scattering are taken into account in order to describe in situ experiments and the good coincidence with measurements in the short-wave region is observed for the optical depth calculated up to the wavenumbers of 20 000 cm −1 . First, an old hypothesis, that the absorption anomaly in water clouds in comparison with traditional modeling should be, in particular, explained by the continuum absorption of water, may be confirmed by the present calculations. Second, since the previous parametrization to be made for the pure water vapor continuum has been saved, our approach based on the radical hypotheses describing the continuum by nonlinear terms has been validated as a successful attempt to decide an important applied problem. On the whole, this enhancement problem of comparison of the absorption measured and modeled in the visible spectral region is presented in two forms, when the excess absorption either of a few orders of magnitude or approximately of 10% is observed for the transparency windows or bands, respectively. The solution of this problem in the present paper is suggested by modeling of the full absorption spectrum (nonlinear continuum+linear absorption contribution mainly from the central part of lines) within the wide spectral region. There is a discussion of the interaction of the microwave band of water with the UV bands of the gases presented and the band enhancement problem, in detail, is considered for the near-infrared band 10 500– 10 900 cm −1 .