Theory of the water vapor continuum and validations

Tipping, R. H.; Ma, Q.

doi:10.1016/0169-8095(94)00028-c

Cited by 57 publications

(46 citation statements)

References 35 publications

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“…The calculation of the far-wing absorption of strong water monomer lines in the theoretical approach by Tipping & Ma [8] (figure 4a) is an order of magnitude smaller than the continuum retrieved here. So, one can assume that either the far-wing absorption by water monomers cannot contribute markedly to the derived continuum in these windows and at the temperatures under discussion or the current theory is significantly in error.…”

Section: Discussionmentioning

confidence: 95%

“…As was stressed earlier, the contribution from the water vapour self-continuum (H 2 O−H 2 O) and from N 2 −N 2 and O 2 −O 2 CIA was excluded from C f . The MTCKD-2.5 model [9,10] and the far-wings model of Tipping & Ma [8] are presented for comparison. Figure 5 shows in more detail the 4 mm (2500 cm −1 ) window.…”

Section: (B) Error Of the Derived Continuummentioning

confidence: 99%

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Water vapour foreign-continuum absorption in near-infrared windows from laboratory measurements

Ptashnik

McPheat

Shine

et al. 2012

Phil. Trans. R. Soc. A.

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For a long time, it has been believed that atmospheric absorption of radiation within wavelength regions of relatively high infrared transmittance (so-called 'windows') was dominated by the water vapour self-continuum, that is, spectrally smooth absorption caused by H 2 O−H 2 O pair interaction. Absorption due to the foreign continuum (i.e. caused mostly by H 2 O−N 2 bimolecular absorption in the Earth's atmosphere) was considered to be negligible in the windows. We report new retrievals of the water vapour foreign continuum from high-resolution laboratory measurements at temperatures between 350 and 430 K in four near-infrared windows between 1.1 and 5 mm (9000-2000 cm −1 ). Our results indicate that the foreign continuum in these windows has a very weak temperature dependence and is typically between one and two orders of magnitude stronger than that given in representations of the continuum currently used in many climate and weather prediction models. This indicates that absorption owing to the foreign continuum may be comparable to the self-continuum under atmospheric conditions in the investigated windows. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by approximately 0.46 W m −2 (or 0.6% of the total clearsky absorption) by using these new measurements when compared with calculations applying the widely used MTCKD (Mlawer-Tobin-Clough-Kneizys-Davies) foreigncontinuum model.

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Section: Discussionmentioning

confidence: 95%

Section: (B) Error Of the Derived Continuummentioning

confidence: 99%

Water vapour foreign-continuum absorption in near-infrared windows from laboratory measurements

Ptashnik

McPheat

Shine

et al. 2012

Phil. Trans. R. Soc. A.

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“…blackbody-anything radiating according to the Planck function; when referring to a calibration source, means a cavity maintained at as constant a temperature as possible, which is designed to absorb every infrared photon entering it (often appears perfectly black to the eye as well); the SPECTRE blackbody allowed its temperature to be continuously varied continuum absorption-an absorption smoothly varying with wavelength (in contrast to line absorption); in earth's atmosphere, due almost entirely to water vapor; probably present throughout the spectrum but can only be observed in "window" regions where line absorption is weak; dominant current theory ascribes it to far wings of strong lines (Tipping and Ma 1995) absorption band-a group of related absorption lines (usually 1000 s) cm -1 -unit of wavenumber; (wavelength in /im) = 10 4 (wavenumber in cm -1 )…”

Section: Field Program Design: Lessons From Spectrementioning

confidence: 99%

“…Line-by-line (LBL) modelers were especially active in trying to resolve their disagreements in the 1984-88 period (LBL models are the most faithful to radiative transfer theory because they make no spectral averaging approximations). Clough et al (1992) describe one such exercise, which showed that the main points of disagreement were (a) where to cut off absorption lines (the theoretical line shape functions extend to infinite wavenumber) and (b) what water vapor continuum formulation to use [see Tipping and Ma (1995) for a review of this subject]. When the LBL modelers used the same line cutoffs and the same continua, their results agreed to 1% or better (or 1-2 W nr 2 ), indicating that the rest of their physics, their computational algorithms, and their absorption line databases were not an important source of disagreement.…”

Section: Intercomparison Of Radiation Codes Used In Climate Models (Imentioning

confidence: 99%

The Spectral Radiance Experiment (SPECTRE): Project Description and Sample Results

Ellingson¹,

Wiscombe²

1996

Bull. Amer. Meteor. Soc.

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The fundamental climatic role of radiative processes has spurred the development of increasingly sophisticated models of radiative transfer in the earth-atmosphere system. Since the basic physics of radiative transfer is rather well known, this was thought to be an exercise in refinement. Therefore, it came as a great surprise when large differences (30-70 W nr 2 ) were found among longwave infrared fluxes predicted by over 30 radiation models for identical atmospheres during the intercomparison of radiation codes used in climate models (ICRCCM) exercise in the mid-1980s. No amount of further calculation could explain these and other intermodel differences; thus, it became clear that what was needed was a set of accurate atmospheric spectral radiation data measured simultaneously with the important radiative properties of the atmosphere like temperature and humidity.To obtain this dataset, the ICRCCM participants charged the authors to develop an experimental field program. So, the authors developed a program concept for the Spectral Radiance Experiment (SPECTRE), organized a team of scientists with expertise in atmospheric field spectroscopy, remote sensing, and radiative transfer, and secured funding from the Department of Energy and the National Aeronautics and Space Administration. The goal of SPECTRE was to establish a reference standard against which to compare models and also to drastically reduce the uncertainties in humidity, aerosol, etc., which radiation modelers had invoked in the past to excuse disagreements with observations. To avoid the high cost and sampling problems associated with aircraft, SPECTRE was designed to be a surface-based program.The field portion of SPECTRE took place 13 November to 7 December 1991, in Coffeyville, Kansas, in conjunction with the FIRE Cirrus II field program, and most of the data have been calibrated to a usable form and will soon appear on a CD-ROM. This paper provides an overview of the data obtained; it also outlines the plans to use this data to further advance the ICRCCM goal of testing the verisimilitude of radiation parameterizations used in climate models.

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“…In the thermal infrared the continuum absorption is large, and numerous parameterization exist to account for it [Roberts et al, 1976;Tipping and Ma, 1994]. In the optical domain, modeling for the continuum absorption results from an extrapolation of the IR spectral domain, for which measurements have been made [Clough et al, 1989].…”

Section: R=mentioning

confidence: 99%

Atmospheric water vapor estimate by a differential absorption technique with the polarisation and directionality of the Earth reflectances (POLDER) instrument

Bouffies¹,

Bréon²,

Tanré³

et al. 1997

J. Geophys. Res.

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Abstract. The polarization and directionality of the Earth reflectances (POLDER) instrument, to be launched in 1996 on the Japanese ADEOS (advanced Earth observing satellite) platform includes a channel which covers the 910 nm water vapor absorption band (near IR), as well as a channel centered at 865 nm. An estimate of the total atmospheric water vapor content can be derived from the ratio of the two reflectance measurements. In addition to the spectroscopic parameterization, the major uncertainties of this estimate result from (1) the surface reflectance spectral signature, (2) scattering by atmospheric aerosol, and (3) the water vapor vertical profile. A radiative transfer model has been developed in order to quantify these uncertainties. From radiative transfer simulations an uncertainty on the order of 10% is expected on the total water vapor amount. An airborne version of the POLDER instrument has been developed and flown over various targets. These targets include semiarid surfaces (Sahel), bog, coniferous and deciduous forest (Boreal forest), and the ocean in the glint direction. Water vapor measurements from radiosondes, concomitant with the POLDER measurements, are available for the method validation. Over water bodies with glint present, an overestimate is found, which is still not understood at present. For other surfaces the comparisons are, in general, in good agreement with the uncertainty analysis.

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Theory of the water vapor continuum and validations

Cited by 57 publications

References 35 publications

Water vapour foreign-continuum absorption in near-infrared windows from laboratory measurements

Water vapour foreign-continuum absorption in near-infrared windows from laboratory measurements

The Spectral Radiance Experiment (SPECTRE): Project Description and Sample Results

Atmospheric water vapor estimate by a differential absorption technique with the polarisation and directionality of the Earth reflectances (POLDER) instrument

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