n most near‐infrared atmospheric windows, absorption of solar radiation is dominated by the water vapor self‐continuum, and yet there is a paucity of measurements in these windows. We report new laboratory measurements of the self‐continuum absorption at temperatures between 293 and 472 K and pressures from 0.015 to 5 atm in four near‐infrared windows between 1 and 4 μm (10000–2500 cm−1); the measurements are made over a wider range of wavenumbers, temperatures, and pressures than any previous measurements. They show that the self‐continuum in these windows is typically one order of magnitude stronger than given in representations of the continuum widely used in climate and weather prediction models. These results are also not consistent with current theories attributing the self‐continuum within windows to the far wings of strong spectral lines in the nearby water vapor absorption bands; we suggest that they are more consistent with water dimers being the major contributor to the continuum. The calculated global average clear‐sky atmospheric absorption of solar radiation is increased by ∼0.75 W/m2 (which is about 1% of the total clear‐sky absorption) by using these new measurements as compared to calculations with the MT_CKD‐2.5 self‐continuum model.
JGR-Atmospheres includes physics and chemistry of the atmosphere, as well as the atmospheric-biospheric, lithospheric, and hydrospheric interface.
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A line tunable deuterium fluoride laser was used to measure the pressure dependence of the water vapor continuum absorption at 25 degree C in the 3.5-4.0- μm spectral region. From measurements of the absorption of 14.3 Torr od deuterium depleted water vapor buffered by several air-broadening pressures, an unexpectedly small foreign-to-self-broadening coefficient of 0.011 with a factor of 2 uncertainty as well as an unusually strong self-contribution for the water vapor continuum absorption were observed. These measurements can be used to infer contributions to the water vapor continuum in the 3-5-μm window from both far wing and aggregate-water-molecule type absorptions.
