Isotopes in Induced Radioactivity (original) (raw)
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Journal of Geophysical Research, 2000
A Fourier transform infrared •(FTIR) spectrometer, operating at 1 cm -1 resolution between 9000 and 24,669 cm-(0.405-1.111 pm) has been used to check the spectral composition of databases that form the basis for most atmospheric absorption parameterizations used in climate models, remote sensing, and other radiative transfer simulations. The spectrometer, operating near sea level under clear skies, obtained relative atmospheric transmission measurements of the direct solar beam by means of a heliostat. The spectroscopic data were compared with a line-by-line radiative transfer model (LBLRTM) calculation of direct solar beam flux, which used a input data a monochromatic model extraterrestrial solar flux spectrum currently in common use. This intercomparison revealed that the extraterrestrial solar flux spectrum contains 266 solar absorption features that do not appear in the data, resulting in an excess of approximately 1.92 W m -2 in the model's solar constant. The intercomparison also revealed 97 absorption features in the data that do not appear in the HITRAN-96 database as used by --2 LBLRTM, resulting in a model underestimate of shortwave absorption of -0.23 W m for a solar zenith angle of 42 ø. These small discrepancies revealed by the intercomparison indicate that current extraterrestrial solar irradiance models and spectroscopic databases used by shortwave atmospheric radiative transfer models are nearly entirely complete for purposes of atmospheric energy budget calculation. Thus clear or cloudy sky "excess absorption" is unlikely to be related to an incomplete identification of atmospheric absorbing gases and their spectroscopic features, at 1 cm -• resolution, for a clean troposphere of normal composition. 1.
Actinic radiation in the terrestrial atmosphere
Journal of Atmospheric and Solar-Terrestrial Physics, 1997
Actinic radiation originating from the Sun drives the photochemistry of the Earth's atmosphere. Surprisingly few measurements have been made of this terrestrial forcing agent which is responsible for such anthropogenically critical issues as the production and loss of atmospheric ozone. This paper describes the status of our knowledge of actinic radiation throughout the middle and lower atmosphere with the goal of summarizing progress to date and identifying future requirements. The focus is mainly on radiation, with wavelengths between 170 and 400 nm, but does include other UV radiation which is deposited in the middle atmosphere. Topics are covered in their natural order, beginning with the solar spectral irradiance above the atmosphere, its transmission through the atmosphere, the component which is multiply scattered, UV radiation reaching the biosphere, and direct measurements of photolysis rates. Concluding remarks include recommendations for additional research.
Infrared Physics, 1977
A method of numerical simulation of transmission and/or emission spectra of the Earth's lower atmosphere is described. The computation is performed, line by line, in the 10 pm-1 mm wavelength range. Six molecular atmospheric absorbers have been considered. The numerical treatment is analyzed and some spectral results are presented. The synthetic data are convolved with an appropriate instrumental function and the line identification problem is discussed to allow comparison with high resolution spectral observations. In addition, we present a method for inverting the emission data, which is applied to determine the vertical distribution of the telluric water vapour and the atmospheric spectral transmission.
Spectrally resolved observations of atmospheric emitted radiance in the H2O rotation band
Geophysical Research Letters, 2008
1] This paper presents the project Earth Cooling by Water Vapor Radiation, an observational programme, which aims at developing a database of spectrally resolved far infrared observations, in atmospheric dry conditions, in order to validate radiative transfer models and test the quality of water vapor continuum and line parameters. The project provides the very first set of far-infrared spectral downwelling radiance measurements, in dry atmospheric conditions, which are complemented with Raman Lidar-derived temperature and water vapor profiles. Citation: Bhawar, R., et al. (2008), Spectrally resolved observations of atmospheric emitted radiance in the H 2 O rotation band, Geophys. Res. Lett., 35, L04812,
2006
Abstract. Contrary to tropospheric CO2 whose oxygen iso-topic composition follows a standard mass dependent rela-tionship, i.e. δ17O∼0.5 δ18O, stratospheric CO2 is preferen-tially enriched in 17O, leading to a strikingly different rela-tion: δ17O∼1.7 δ18O. It has been shown repeatedly that the isotope anomaly is inherited from O3 via photolytically pro-duced O(1 D) that undergoes isotope exchange with CO2 and the anomaly may well serve as a tracer of stratospheric chem-istry if details of the exchange mechanism are understood. We have studied the photochemical isotope equilibrium in UV-irradiated O2-CO2 and O3-CO2 mixtures to quantify the transfer of the anomaly from O3 to CO2 at room tempera-ture. By following the time evolution of the oxygen isotopic compositions of CO2 and O2 under varying initial isotopic compositions of both, O2/O3 and CO2, the isotope equilibria
Radiative emission of solar features in the Ca II K line: comparison of measurements and models
Astronomy & Astrophysics, 2010
Context. The atmospheric composition of transiting exoplanets can be characterized during transit by spectroscopy. Detections of several chemical species have previously been reported in the atmosphere of gaseous giant exoplanets. For the transit of an Earth twin, models predict that biogenic oxygen (O2) and ozone (O3) atmospheric gases should be detectable, as well as water vapour (H2O), a molecule linked to habitability as we know it on Earth. Aims. The aim is to measure the Earth radius versus wavelength λ-or the atmosphere thickness h(λ)-at the highest spectral resolution available to fully characterize the signature of Earth seen as a transiting exoplanet. Methods. We present observations of the Moon eclipse of December 21, 2010. Seen from the Moon, the Earth eclipses the Sun and opens access to the Earth atmosphere transmission spectrum. We used two different ESO spectrographs (HARPS and UVES) to take penumbra and umbra high-resolution spectra from ≈ 3100 to 10400Å. A change of the quantity of water vapour above the telescope compromised the quality of the UVES data. We corrected for this effect in the data processing. We analyzed the data by three different methods. The first method is based on the analysis of pairs of penumbra spectra. The second makes use of a single penumbra spectrum, and the third of all penumbra and umbra spectra. Results. Profiles h(λ) are obtained with the three methods for both instruments. The first method gives the best result, in agreement with a model. The second method seems to be more sensitive to the Doppler shift of solar spectral lines with respect to the telluric lines. The third method makes use of umbra spectra which bias the result by increasing the overall negative slope of h(λ). It can be corrected for this a posteriori from results with the first method. The three methods clearly show the spectral signature of the Rayleigh scattering in the Earth atmosphere and the bands of H2O, O2, and O3. Sodium is detected. Assuming no atmospheric perturbations, we show that the E-ELT is theoretically able to detect the O2 A-band in 8 h of integration for an Earth twin at 10 pc. Conclusions. Biogenic O2, O3, and water vapour are detected in Earth observed as a transiting planet, and, in principle, would be within reach of the E-ELT for an Earth twin at 10 pc.
Weak ozone isotopic absorption in the region from high resolution FTIR solar spectra
Journal of Quantitative Spectroscopy and Radiative Transfer, 2002
Isotopic ozone lines of 16 O 16 O 17 O and 16 O 17 O 16 O in the 5 m region are identiÿed for the ÿrst time in balloon-borne high-resolution (0:003 cm −1) solar absorption spectra. A few of these lines also are observed in ground-based spectra. These lines need to be included in analysis of atmospheric absorption spectra, in addition to the recently identiÿed 16 O 16 O 18 O; 16 O 18 O 16 O and 16 O 12 C 34 S lines in this region.
J Quant Spectrosc Radiat, 2004
A theoretical model for the prediction of CO 2 absorption in both central and wing regions of infrared absorption bands was presented in the companion paper I. It correctly accounts for line-mixing e ects and was validated by comparisons with laboratory spectra in the 600-1000 cm −1 region. This quality was conÿrmed using atmospheric transmissions measured by solar occultation experiments in the second paper. The present work completes these studies by now considering atmospheric emission in the 10-20 m range. Comparisons are made between computed atmospheric radiances and measurements obtained using four di erent Fourier transform experiments collecting spectra for nadir, up-looking, as well as limb (from balloon and satellite) geometries. Our results conÿrm that using a Voigt model can lead to very large errors that a ect the spectrum more than 300 cm −1 away from the center of the CO 2 2 band. They also demonstrate the capability of our model to represent accurately the radiances in the entire region for a variety of atmospheric paths. This success opens interesting perspectives for the sounding of pressure and temperature proÿles, particularly at low altitudes. Another beneÿt of the quality of the model should be an increased accuracy in the retrieval of atmospheric state parameters from broad features in the measured spectra (clouds, aerosols, heavy trace gases). ?
Infrared Radiation in the Mesosphere and Lower Thermosphere: Energetic Effects and Remote Sensing
Surveys in Geophysics, 2012
This paper discusses the formation mechanisms of infrared radiation in the mesosphere and lower thermosphere (MLT), the energetic effects of the radiative absorption/emission processes, and the retrieval of atmospheric parameters from infrared radiation measurements. In the MLT and above, the vibrational levels of the molecules involved in radiative transitions are not in local thermodynamic equilibrium (LTE) with the surrounding medium, and this then requires specific theoretical treatment. The non-LTE models for CO 2 , O 3 , and H 2 O molecules are presented, and the radiative cooling/heating rates estimated for five typical atmospheric scenarios, from polar winter to polar summer, are shown. An optimization strategy for calculating the cooling/heating rates in general circulation models is proposed, and its accuracy is estimated for CO 2 . The sensitivity of the atmospheric quantities retrieved from infrared observations made from satellites to the non-LTE model parameters is shown.