New laboratory intercomparison of the ozone absorption coefficients in the mid-infrared (10 µm) and ultraviolet (300-350 nm) spectral regions.

Knowing the ozone absorption cross sections in the ultraviolet and infrared spectral range, with an accuracy of better than 1%, is of the utmost importance for atmospheric remote-sensing applications. For this reason, various ozone intensity intercomparisons and measurements have been published these last years. However, the corresponding results proved not to be consistent and thus have raised a controversial discussion in the community of atmospheric remote-sensing. This study, where great care has been taken to avoid any possible error, reports a new laboratory intercomparison of the ozone absorption coefficients in the mid-infrared (10 µm) and ultraviolet (300-350 nm) spectral regions. It gives a new piece of information to the puzzling problem concerning the ozone IR and UV cross sections and confirms that the IR and UV cross sections recommended in the literature are in disagreement of about 4%.

Laboratory intercomparison of the ozone absorption coefficients in the mid-infrared (10 microm) and ultraviolet (300-350 nm) spectral regions.

For the measurement of atmospheric ozone concentrations, the mid-infrared and ultraviolet regions are both used by ground-, air-, or satellite-borne instruments. In this study we report the first laboratory intercomparison of the ozone absorption coefficients using simultaneous measurements in these spectral regions. The intercomparison shows good agreement (around 98.5%) between the HITRAN 2000 recommendation for the mid-infrared and the most reference measurements in the ultraviolet regions, whereas systematic differences of about 5.5% are observed when using the recommendation of HITRAN2003 for the mid-infrared. Possible reasons for this discrepancy are discussed. Future measurements are clearly needed to resolve this issue.

High-Resolution Infrared, Microwave, and Submillimeter-Wave Study of FClO(2) in the nu(2), nu(3), nu(4), and nu(6) Excited States.

A high-resolution analysis of the {nu(2), nu(3)} and {nu(4), nu(6)} bands of the two isotopomers of chloryl fluoride F(35)ClO(2) and F(37)ClO(2) has been carried out for the first time using simultaneously infrared spectra recorded around 16&mgr;m and 26&mgr;m with a resolution of ca. 0.003 cm(-1) and microwave and submillimeter-wave transitions occurring within the vibrational states 2(1), 3(1), 4(1), and 6(1). Taking into account the Coriolis resonances which link the rotational levels of the {2(1), 3(1)} and the {4(1), 6(1)} interacting states, it was possible to reproduce very satisfactorily the observed transitions and to determine accurate vibrational energies and rotational constants for the upper states 2(1), 3(1), 4(1), and 6(1) of both the (35)Cl and (37)Cl isotopic species. Copyright 2001 Academic Press.

The v(1)+v(3) Bands of the (16)O(17)O(16)O and (16)O(16)O(17)O Isotopomers of Ozone.

Using 0.002 cm(-1) resolution Fourier transform absorption spectra of an (17)O enriched ozone sample, an extensive analysis of the v(1)+v(3) bands of the (16)O(17)O(16)O and (16)O(16)O(17)O isotopomers of ozone has been performed for the first time. The experimental rotational levels of the (101) vibrational states were satisfactorily reproduced using a Hamiltonian matrix that takes into account the observed rovibrational resonances. More precisely, for (16)O(17)O(16)O, as for the other C(2v)-type ozone isotopomers, it was necessary to account for the Coriolis type resonances linking the (101) rotational levels with the levels of the (200) and (002) vibrational states and the Darling-Dennison interaction coupling the levels of (200) with those of (002). For the C(s)-type isotopomer, namely (16)O(16)O(17)O, as for (16)O(16)O(18)O and (16)O(18)O(18)O, it proved necessary to also account for an additional DeltaK(a)&equals+/-2 resonance involving the rotational levels from (101) and (002) (J.-M. Flaud and R. Bacis, Spectrochimica Acta Part A 54, 3-16 (1998)). Using a Hamiltonian matrix which takes these resonances explicitly into account, precise vibrational energies and rotational and coupling constants were deduced, leading to the following band centers: v(0)(v(1)+v(3))=2078.3496 cm(-1) for (16)O(17)O(16)O and v(0)(v(1)+v(3))=2098.8631 cm(-1) for (16)O(16)O(17)O. Copyright 2001 Academic Press.

Absolute Intensities of the nu(1) and nu(3) Bands of (16)O(3).

New experimental data on the nu(1) and nu(3) bands of (16)O(3) improving the value of absolute line intensities have been obtained. The intensities of 295 lines have been measured with an average accuracy between 2.5% and 3% and the rotational expansion of the transition moment operators for the nu(1) and nu(3) bands has been deduced. Finally, a complete listing of line intensities has been computed with an intensity cutoff of 1x10(-25) cm(-1)/molecule cm(-2). Copyright 2001 Academic Press.

Optimized forward model and retrieval scheme for MIPAS near-real-time data processing.

An optimized code to perform the near-real-time retrieval of profiles of pressure, temperature, and volume mixing ratio (VMR) of five key species (O(3), H(2)O, HNO(3), CH(4), and N(2)O) from infrared limb spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) experiment on board the European Space Agency (ESA) Environmental Satellite ENVISAT-1 was developed as part of a ESA-supported study. The implementation uses the global fit approach on selected narrow spectral intervals (microwindows) to retrieve each profile in sequence. The trade-off between run time and accuracy of the retrieval was optimized from both the physical and the mathematical points of view, with optimizations in the program structure, in the radiative transfer model, and in the computation of the retrieval Jacobian. The attained performances of the retrieval code are noise error on temperature <2 K at all the altitudes covered by the typical MIPAS scan (8-53 km with 3-km resolution), noise error on tangent pressure <3%, and noise error on VMR of the target species <5% at most of the altitudes covered by the standard MIPAS scan, with a total run time of less than 1 min on a modern workstation.

Optimized spectral microwindows for data analysis of the Michelson Interferometer for Passive Atmospheric Sounding on the Environmental Satellite.

For data analysis of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) atmospheric limb emission spectroscopic experiment on Environmental Satellite microwindows, i.e., small spectral regions for data analysis, have been defined and optimized. A novel optimization scheme has been developed for this purpose that adjusts microwindow boundaries such that the total retrieval error with respect to measurement noise, parameter uncertainties, and systematic errors is minimized. Dedicated databases that contain optimized microwindows for retrieval of vertical profiles of pressure and temperature, H2O, O3, HNO3, CH4, N2O, and NO2 have been generated. Furthermore, a tool for optimal selection of subsets of predefined microwindows for specific retrieval situations has been provided. This tool can be used further for estimating total retrieval errors for a selected microwindow subset. It has been shown by use of this tool that an altitude-dependent definition of microwindows is superior to an altitude-independent definition. For computational efficiency a dedicated microwindow-related list of spectral lines has been defined that contains only those spectral lines that are of relevance for MIPAS limb sounding observations.

Rotational and vibrational dependences of collisional linewidths in the nnu(2)-(n-1)nu(2) hot bands of H2O from Fourier-transform flame spectra.

The collisional widths of ~ 160 transitions belonging mainly to the 2nu(2)-nu(2), 3nu(2)-2nu(2), and 4nu(2)-3nu(2) hot bands of the H(2)(16)O molecule have been measured on Fourier-transform air-methane flame spectra at 2000 K and analyzed, showing a strong decrease in the collisional widths when the rotational quantum number J increases, as well as a nonnegligible decrease of the collisional widths when the nu(2) vibrational quantum number increases.

Measurements of collisional linewidths in the nu(2) band of H(2)O from Fourier-transformed flame spectra.

The collisional widths of more than 200 transitions belonging to the v(2) band of the H(2)O molecule were measured by using the Fourier-transformed spectra of an air-methane flame at 2000 K. A nonlinear least-squares method was used to determine the line widths for a wide range of J (up to 28) and K(a) (up to 14) quantum number values. Finally, an analysis of the results as functions of J and K(a) is presented.

Improved line parameters for ozone bands in the 10-microm spectral region.

A complete update of spectroscopic line parameters for the 10-microm bands of ozone is reported. The listing contains calculated positions, intensities, lower state energies, and air- and self-broadened halfwidths of more than 53,000 lines. The results have been generated using improved spectroscopic parameters obtained in a number of recent high resolution laboratory studies. A total of eighteen bands of (16)O(3) (sixteen hot bands plus the nu(1) and nu(3) fundamentals) are included along with the nu(1) and nu(3) fundamentals of both (16)O(16)O(18)O and (16)O(18)O(16)O. As shown by comparisons of line-by-line simulations with 0.003-cm(-1) resolution balloon-borne stratospheric solar spectra, the new parameters greatly improve the accuracy of atmospheric calculations in the 10-microm region, especially for the isotopic (16)O(16)O(18)O and (16)O(18)O(16)O lines.

The HITRAN database: 1986 edition.

A description and summary of the latest edition of the AFGL HITRAN molecular absorption parameters database are presented. This new database combines the information for the seven principal atmospheric absorbers and twenty-one additional molecular species previously contained on the AFGL atmospheric absorption line parameter compilation and on the trace gas compilation. In addition to updating the parameters on earlier editions of the compilation, new parameters have been added to this edition such as the self-broadened halfwidth, the temperature dependence of the air-broadened halfwidth, and the transition probability. The database contains 348043 entries between 0 and 17,900 cm(-1). A FORTRAN program is now furnished to allow rapid access to the molecular transitions and for the creation of customized output. A separate file of molecular cross sections of eleven heavy molecular species, applicable for qualitative simulation of transmission and emission in the atmosphere, has also been provided.

AFGL atmospheric absorption line parameters compilation: 1982 edition.

The latest edition of the AFGL atmospheric absorption line parameters compilation for the seven most active infrared terrestrial absorbers is described. Major modifications to the atlas for this edition include updating of water-vapor parameters from 0 to 4300 cm(-1), improvements to line positions for carbon dioxide, substantial modifications to the ozone bands in the middle to far infrared, and improvements to the 7- and 2.3-microm bands of methane. The atlas now contains approximately 181,000 rotation and vibration-rotation transitions between 0 and 17,900 cm(-1). The sources of the absorption parameters are summarized.