Absorption Of Radiation In Atmosphere Research Articles

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

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 μm (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 clear-sky absorption) by using these new measurements when compared with calculations applying the widely used MTCKD (Mlawer-Tobin-Clough-Kneizys-Davies) foreign-continuum model.

Bandwidth Limitations of Nb/AlN/Nb SIS Mixers Around 700 GHz

We study, using niobium-technology, the bandwidth of SIS mixers operating at frequencies close to the energy-gap frequency. Microstriplines of niobium-silicon dioxide-niobium have different properties for the top and bottom superconductor, which we find to depend on the used fabrication process. Replacing the AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> tunnel barrier by AlN, the bandwidth increases by 53%. The measurements, using a Fourier Transform Spectrometer (FTS) and performed in ambient air, demonstrate that the bandwidth is no longer limited by the tuning circuit but by the atmospheric absorption of radiation. Excellent noise temperatures are found over a full band of 600 to 720 GHz.

Evaluation of suitable spectral intervals for near-IR laboratory detection of water vapour continuum absorption

The water vapour continuum absorption is an important component of molecular absorption of radiation in atmosphere. However, uncertainty in knowledge of the value of the continuum absorption at present can achieve 100% in different spectral regions leading to an error in flux calculation up to 3–5 W/m 2 global mean. This work uses line-by-line calculations to reveal the best spectral intervals for experimental verification of the CKD water vapour continuum models in the currently least-studied near-infrared spectral region. Possible sources of errors in continuum retrieval taken into account in the simulation include the sensitivity of laboratory spectrometers and uncertainties in the spectral line parameters in HITRAN-2004 and Schwenke–Partridge database. It is shown that a number of micro-windows in near-IR can be used at present for laboratory detection of the water vapour continuum with estimated accuracy from 30% to 5%.

Effects of convection on the removal of the multiplicity of stable states in one‐dimensional vertical models

AbstractHere I develop a model of a radiative–convective atmosphere with both radiative and convective schemes highly simplified. The atmospheric absorption of radiation at selective wavelengths makes use of constant mass absorption coefficients in finite width spectral bands. The convective regime is introduced by using a prescribed lapse rate in the troposphere. The main novelty of the radiative–convective model developed here is that it is solved without using any angular approximation for the radiation field. The solution obtained in the purely radiation mode (i.e. with convection ignored) leads to multiple equilibria of stable states, being very similar to some results recently found in simple models of planetary atmospheres. However, the introduction of convective processes removes the multiple equilibria of stable states. This shows the importance of taking convective processes into account even for qualitative analyses of planetary atmospheres. Copyright © 2004 Royal Meteorological Society.

Absorption of visible radiation in atmosphere containing mixtures of absorbing and nonabsorbing particles: erratum

Recent measurements of the single-scattering albedo omega(0) of tropospheric aerosols indicate the presence of a strongly absorbing material which has tentatively been identified as graphitic carbon (soot). Theoretical calculations, based on several different models of the way in which soot might be mixed with other aerosol materials, show that a minimum of 20% soot by volume is necessary to achieve the observed urban value of omega(0) = 0.6. Rural values of the order of 0.8 can be accounted for with 1-5% soot by volume. These same values of omega can be produced by similar amounts of the iron oxide magnetite, which is shown to be virtually indistinguishable from soot by optical measurements performed on bulk samples. Calculations of phase functions for various mixtures of soot also indicate the difficulty of determining aerosol composition by optical scattering techniques. The climatic effects of these absorbing aeorosols are computed using a simple one-layer model, and the results suggest that heating rates in urban pollution layers may be of the order of 4 K/day.