Recent Developments in the Water Vapor Continuum

A key development in the understanding of radiative transfer in the longwave was the introduction of the CKD continuum model (Clough et al. 1989), the success of which effectively ended speculation that there is significant longwave continuum absorption due to water vapor dimers or multimers. With the water vapor continuum defined as any observed absorption due to water vapor not attributable to the Lorentz line contribution within 25 cm of each line, a water vapor monomer line shape formalism was semi-empirically derived and consistently applied to all water vapor lines from the microwave to the shortwave. The success of this approach, which employed a common line shape for all spectral lines, led to the interpretation that water vapor continuum absorption was due to the intermediate and far wings of allowed transitions of the water vapor monomer. The current research effort modifies part of this interpretation, attributing a substantial portion of the continuum to collision-induced transitions of the water vapor monomer instead of the super-Lorentzian behavior of the intermediate wings of allowed transitions.