3 an experimental nitrogen-broadened spectrum is compared with its theoretical counterparts. Figure 2 is a comparison with theoretical calculations of the pure water vapor spectrum. 1 the spectrum of pure water vapor observed by us at 123 torr and 339 K broadened by 639 torr of N 2 is shown for a path length of 39 m. We discuss the above descriptions of the continuum absorption using some data ( Figs.
The fragmentary evidence which exists seems to suggest that the self-broadening coefficient increases much more rapidly with decreasing temperature than the air-broadening component. 1 A totally satisfactory theoretical explanation, which is unbiased in the sense that it is not based on a single set of experimental data from a preferred laboratory, does not exist and experimental evidence remains inconclusive. The temperature dependence of neither of the broadening coefficients has been firmly established. If k 1 v ( T) is more sensitive to changes in T than k 1 v( T), and since the water vapor content is itself highly variable in the planetary atmosphere depending upon local conditions, the term k 2 v( T)e 2 in the expression for the opacity may prove to be a more sensitive gauge of the contribution made by water vapor continuum to the thermal infrared flux than k 1 v( T) pe.
This is in stark contrast to the absorption normally associated with other infrared gaseous constituents of the atmosphere. e-type absorption can be dominant if k 2 v( T) ≫ k 1 v (T) even though e≪ p. The optical depth being proportional to the product of the absorption coefficient k v( T, p, e)and the absorber amount indicated by e, it is clear that the continuum opacity is dependent upon k 2 v( T) e 2. Atmospheric opacity in the window region, if governed by water vapor's continuum alone, will be determined by the optical depth of moist air columns. Bignell chose to call the e-dependent absorption “ e-type absorption” for want of a better name. Where k 1 vis the absorption coefficient at unit partial pressure of dry air (the air-broadening component) and k 2 vis the absorption coefficient at unit partial pressure of water vapor (the self-broadening component). K v ( T, p, e ) = k 1 v ( T ) p + k 2 v ( T ) e ,
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