A formulation is developed in which the contribution of the far wings of collisionallybroadened spectral lines to the water vapor continuum absorption is established. The effects of deviations from the impact (Lorentz) line shape due to duration of collision effects are treated semi-empirically to provide agreement with experimental results for the continuum absorption and its temperature-dependence. The continua due to both water-water molecular broadening (self-broadening ) and water-air molecular broadening (foreign broadening) are discussed. Several atmospheric validations of the present approach are presented.
Attention is given to all processes extending from the earth surface to the tropopause, but special emphasis continues to be devoted to the physics of clouds and precipitation, i.e. atmospheric aerosols; microphysical processes; cloud dynamics and thermodynamics; numerical simulation of cloud processes; clouds and radiation; meso- and macrostructure of clouds and cloud systems, and weather modification.
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The continuum absorption by H2O has several characteristics that are common throughout the windows in the infrared and millimeter-wave regions. Values of the continuum absorption coefficient calculated on the basis of simple, widely used line shapes may differ greatly from observed values in the windows between strong absorption lines. The temperature dependence of this absorption is also not predictable from present day understanding of line shapes or of dieters, which may also contribute. The shapes of self-broadened H2O lines are quite different from those of N2-broadened lines, and the difference increases with increasing distance from the centers of the lines. Data obtained from laboratory samples and from atmospheric paths are presented to compare the various windows in the infrared and millimeter regions.
