Showing papers in "Journal of Quantitative Spectroscopy & Radiative Transfer in 1998"
TL;DR: A computer-accessible catalog of submillimeter, millimeter, and microwave spectral lines in the frequency range between 0 and 10 000 GHz (i.e. wavelengths longer than 30 μm) that has been constructed by using theoretical least-squares fits of published spectral lines to accepted molecular models.
Abstract: This paper describes a computer-accessible catalog of submillimeter, millimeter, and microwave spectral lines in the frequency range between 0 and 10 000 GHz (i.e. wavelengths longer than 30 μm). The catalog can be used as a planning guide or as an aid in the identification and analysis of observed spectral lines in the interstellar medium, the Earth’s atmosphere, and the atmospheres of other planets. The information listed for each spectral line includes the frequency and its estimated error, the intensity, the lower state energy, and the quantum number assignment. The catalog is continuously updated and at present has information on 331 atomic and molecular species and includes a total of 1 845 866 lines. The catalog has been constructed by using theoretical least-squares fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariance. Future versions of this catalog will add more atoms and molecules and update the present listings as new data appear. The catalog is available on-line via anonymous FTP at spec.jpl.nasa.gov and on the world wide web at http: //spec.jpl.nasa.gov.
2,098 citations
TL;DR: The data and features that have been added or replaced since the previous edition of HITRAN are described, including instances of critical data that are forthcoming.
Abstract: Since its first publication in 1973, the HITRAN molecular spectroscopic database has been recognized as the international standard for providing the necessary fundamental spectroscopic parameters for diverse atmospheric and laboratory transmission and radiance calculations. There have been periodic editions of HITRAN over the past decades as the database has been expanded and improved with respect to the molecular species and spectral range covered, the number of parameters included, and the accuracy of this information. The 1996 edition not only includes the customary line-by-line transition parameters familiar to HITRAN users, but also cross-section data, aerosol indices of refraction, software to filter and manipulate the data, and documentation. This paper describes the data and features that have been added or replaced since the previous edition of HITRAN. We also cite instances of critical data that are forthcoming.
1,846 citations
TL;DR: A detailed description of modern ¹-matrix FORTRAN codes which incorporate all recent developments, are publicly available on the World Wide Web, and are, apparently, the most efficient and powerful tool for accurately computing light scattering by randomly oriented rotationally symmetric particles is provided.
Abstract: We describe in detail a software implementation of a current version of the ¹-matrix method for computing light scattering by polydisperse, randomly oriented, rotationally symmetric particles. The FORTRAN ¹-matrix codes are publicly available on the World Wide We ba thttp://www.giss.nasa.gov/&crmim .W egiv eal lnecessar yformulas ,describ einpu tand output parameters, discuss numerical aspects of ¹-matrix computations, demonstrate the capabilities and limitations of the codes, and discuss the performance of the codes in comparison with other available numerical approaches. Published by Elsevier Science Ltd. 1. I NTRODUCTION The ¹-matrix method is a powerful exact technique for computing light scattering by nonspherical particles based on numerically solving Maxwell's equations. Although the method is, potentially, applicable to any particle shape, most practical implementations of the technique pertain to bodies of revolution. The method was initially developed by Waterman and has been significantly improved as described in Refs. 2—6. Specifically, Refs. 4 and 6 extend the method to much larger size parameters and aspect ratios, Ref. 2 presents an efficient analytical procedure for computing the scattering properties of randomly oriented particles, Ref. 3 describes an automatic convergence procedure convenient in massive computer calculations for particle polydispersions, and Ref. 5 presents benchmark ¹-matrix computations for particles with non-smooth surfaces (finite circular cylinders). A general review of the ¹-matrix method can be found in Ref. 7. In this paper we provide a detailed description of modern ¹-matrix FORTRAN codes which incorporate all recent developments, are publicly available on the World Wide Web, and are, apparently, the most efficient and powerful tool for accurately computing light scattering by randomly oriented rotationally symmetric particles. For the first time, we collect in one place all necessary formulas, discuss numerical aspects for ¹-matrix computations, describe the input and output parameters, and demonstrate the capabilities and limitations of the codes. The paper is intended to serve as a detailed user guide to a versatile tool suitable for a wide range of practical applications. We specifically target the users who are interested in practical applications of the ¹-matrix method rather than in details of its mathematical formulation.
815 citations
TL;DR: In this article, the authors measured the NO2 absorption cross-section from 42 000 to 10 000 cm−1 (238-1000 nm) with a Fourier transform spectrometer (at the resolution of 2 cm− 1, 0.01 nm at 240 nm to 0.2 nm at 1000 nm).
Abstract: The NO2 absorption cross-section has been measured from 42 000 to 10 000 cm−1 (238–1000 nm) with a Fourier transform spectrometer (at the resolution of 2 cm−1, 0.01 nm at 240 nm to 0.2 nm at 1000 nm) and a 5 m temperature controlled multiple reflection cell. The uncertainty on the cross-section is estimated to be less than 3% below 40 000 cm−1 (λ > 250 nm) at 294 K, 3% below 30 000 cm−1 (λ > 333 nm) at 220 K, but reaches 10% for higher wavenumbers. Temperature and pressure effects have been observed. Comparison with data from the literature generally shows a good agreement for wavenumbers between 37 500 and 20 000 cm−1 (267–500 nm). Outside these limits, the difference can reach several percent.
684 citations
TL;DR: In this paper, the Global Ozone Monitoring Experiment (GOME) Flight-Model (FM) satellite spectrometer was used to measure the absorption cross sections of O3 in the 231-794nm range.
Abstract: Absorption cross sections of O3 in the 231–794 nm range have been measured at temperatures between 202 and 293 K using the Global Ozone Monitoring Experiment (GOME) Flight-Model (FM) satellite spectrometer. The GOME FM spectra have a spectral resolution of about 0.2 nm below 400 nm and of about 0.3 nm above 400 nm, and were recorded covering simultaneously the Hartley, Huggins, and Chappuis bands centered around 255, 340, and 610 nm, respectively. The variation of the O3 absorption cross sections was investigated over the entire spectral range 231–794 nm. The new cross sections are important as reference data for atmospheric remote-sensing of O3 and other trace gases.
476 citations
TL;DR: The Spherical Top Data System (STDS) as mentioned in this paper is a UNIX package for the simulation of spherical top spectra that allows the non-expert user to calculate spectra from the results of the high resolution analyses performed over the recent decades on this type of molecules.
Abstract: The Spherical Top Data System (STDS) software package for the simulation of spherical top spectra is presented. It consists of a single UNIX script with self-explanatory arguments allowing the non-expert user to calculate spectra from the results of the high resolution analyses performed over the recent decades on this type of molecules. More than one hundred parameter files are presently available including various band systems of 16 molecular species (among which methane is the most documented) and various types of calculations: rovibrational energy levels, i.r. absorption, Raman scattering and Stark coefficients. STDS is freely accessible by anonymous ftp at jupiter.u-bourgogne.fr. The basic instructions to get, install and execute STDS are explained. The current status of the STDS content is described.
244 citations
TL;DR: In this article, the filling-in of Fraunhofer and gas absorption features, resulting from Rotational Raman scattering (RRS), explains to high accuracy the Ring effect.
Abstract: One significant limitation to the accuracy of the remote sensing of trace gas constituents in the atmosphere, using UV-visible spectroscopy and scattered sunlight, has often been a reliable knowledge of the so-called Ring effect. In this study it is demonstrated that the filling-in of Fraunhofer and gas absorption features, resulting from Rotational Raman scattering (RRS), explains to high accuracy the Ring effect. A radiative transfer model has been adapted to include RRS and carefully validated by comparison with Ring effect data by other models and from ground-based and satellite data. The analysis of the principle components of the simulated Ring spectra enabled the Fraunhofer and gas absorption filling-in to be separated. This yields a simple, and therefore computational fast, parameterization of the Ring effect suitable for trace gas retrievals. This approach was tested for the retrieval of NO 2 which is considered to be a worst case with respect to absorption feature filling-in for a trace gas retrieved from scattered light. Analysis of the errors in the vertical column of NO 2 derived using differential optical absorption spectroscopy (DOAS) technique indicate that they are dependent on the amount of NO 2 present in the atmosphere when regarding the experimental Ring spectra. This implies that calculated Ring spectra may be superior for DOAS retrievals, compared to the experimentally determined Ring spectra.
206 citations
TL;DR: In this paper, the authors compared the scattering matrices of perfect and imperfect hexagonal ice crystals with those of polycrystals and showed that the optical properties of these imperfect crystals are sensitive to the aspect ratio and particle size as well as to the allowed deviation from the perfect shape.
Abstract: Scattering matrices of perfect and imperfect hexagonal ice crystals are presented and compared to those of so-called polycrystals, proposed by Macke et al. [1] . Scattering matrices of imperfect hexagonal crystals are calculated using statistical deviations of ray paths during the ray tracing in perfect hexagonal crystals. At a certain degree of deviation, the resulting scattering matrix becomes similar to that of polycrystals. Therefore, this method forms a link between perfect hexagonal columns and polycrystals. The optical properties of these imperfect crystals are sensitive to the aspect ratio (and thus to particle size) as well as to the allowed deviation from the perfect shape. This approach to simulate imperfect ice crystals introduces new possibilities for interpretation of satellite measurements.
122 citations
TL;DR: In this paper, a spectral line parameter set for the OH X 2 II-X 2 II transitions for Δv = 0.., 6, with v = 0.5 and J max = 49.5 is presented.
Abstract: New spectral line parameters have been generated for the OH X 2 II–X 2 II transitions for Δv = 0.., 6, with v ′ = 0.., 10, and J max = 49.5. HITRAN type line parameter sets with low intensity cutoffs are provided at 296 and 6000 K. Recent improvements in line intensities and line positions have been incorporated into the calculations.
116 citations
TL;DR: In this article, a reduced effective Hamiltonian built up to sixth order in the Amat-Nielsen ordering scheme has been obtained from an effective Hamiltonians describing all vibrational-rotational energy levels in the ground electronic state.
Abstract: About 13 000 experimental lines of the principal isotopic species of CO2 selected from the literature have been used to derive about 100 parameters of a reduced effective Hamiltonian built up to sixth order in the Amat–Nielsen ordering scheme. This Hamiltonian has been obtained from an effective Hamiltonian describing all vibrational–rotational energy levels in the ground electronic state and containing in explicit form all resonance interaction terms due to the approximate relations between harmonic frequencies ω1≈2ω2andω3≈ω1+ω2. An RMS deviation of 0.001 cm-1 has been achieved in the fitting. In order to test its predictive capabilities, the model has been used to calculate the line positions of six bands: 05511←05501, 1005(1, 2)←1004(1, 2), 1006(1, 2)←1005(1, 2), and 20033←00001, which are compared with experimental lines not included in the data set. The results are discussed and compared with the predictions of the Direct Numerical Diagonalization technique.
113 citations
TL;DR: In this paper, the halfwidth and line shift of water vapor perturbed by N2, O2, CO2, and H2 are calculated based on a complex implementation of the formalism of Robert and Bonamy.
Abstract: Calculations of the halfwidth and line shift of water vapor perturbed by N2, O2, CO2, and H2 based on a complex implementation of the formalism of Robert and Bonamy are made. The potentials employ the leading terms of the electrostatic potential, a Lennard -Jones (6–12) atom-atom potential, and the induction and dispersion components of the isotropic potential. The dynamics of the collisions are correct to second order in time. The results are compared with measurements and very good agreement is observed for both halfwidths and line shifts. A new feature in this approach is that the real and imaginary components of the S matrix affect both the halfwidth and the line shift. It is shown here that the imaginary parts of the S matrix strongly affect the calculated halfwidths for some of the systems considered.
TL;DR: In this paper, the authors reported self-broadened linewidths and pressure-induced frequency-shifts of water vapor lines in the spectral region between 590 and 2400 cm−1.
Abstract: This experimental study reports self-broadened linewidths and pressure-induced frequency-shifts of water vapor in the spectral region between 590 and 2400 cm−1. Over 1900 vibration–rotation transitions have been measured at 0.0054 cm−1 resolution using the Fourier transform spectrometer at Kitt Peak National Observatory. Self-broadening parameters have been obtained for the (000)–(000), (010)–(010), (010)–(000), (020)–(010), and (100)–(010) vibrational bands of H216O, H218O, and H217O. The observed widths range from 0.52 to 0.1 cm−1 atm−1, and the pressure shifts fall between ±0.05 cm−1 atm−1. The present linewidth coefficients are compared with previously measured and computed values given in the available literature. There have been no prior studies of self-broadened frequency-shifts of water vapor lines of this spectral region.
TL;DR: In this article, the authors give a short introduction to three very different types of electromagnetic scattering methods and have a look at the applicabilities and shortcomings of each method, including Discrete Dipole Approximation (DDA), alias Coupled Dipole Method (CDM), Finite Difference Time Domain (FDTD), Extended Boundary Condition Method (EBCM), etc.
Abstract: There are various methods to compute electromagnetic scattering by arbitrarily shaped particles. The aim of this article is merely to give a short introduction to three very different types of methods and have a look at the applicabilities and shortcomings of each. At first some comments are made. • to the Discrete Dipole Approximation (DDA), alias Coupled Dipole Method (CDM), as a special form of the Volume Integral Equation Method (VIE); • to the Finite Difference Time Domain (FDTD) and • to the Extended Boundary Condition Method (EBCM). As an example the results and the parameters of different codes for a cube are compared to give just a hint of the computational demands.
TL;DR: In this article, a linearization of the radiative transfer equation allows to compute the weighting functions directly without the use of numerical perturbation schemes, which can be used for the retrieval of ozone and temperature vertical profiles from satellite measurements.
Abstract: Novel mathematical procedures for the efficient calculation of weighting functions inside finite differencing radiative transfer models are presented. Linearization of the radiative transfer equation allows to compute the weighting functions directly without the use of numerical perturbation schemes. The methods developed have been implemented in the finite-differencing model GOMETRAN. Validation of the quasi-analytical computations of the weighting functions has been achieved by comparison with results using numerical perturbation methods from finite-differencing and doubling-adding. An interpretation of the weighting functions is presented and outlines their relationship with air mass factors. Finally, the weighting function technique is applied to the retrieval of ozone and temperature vertical profiles from satellite measurements.
TL;DR: In this article, line positions, intensities, transition-moment squared, and lower state energies are calculated for the three most abundant isotopomers of the oxygen molecule in the terrestrial atmosphere, 1602, 80'60, and 70'60.
Abstract: Line positions, intensities, transition-moment squared, and lower state energies are calculated for the three most abundant isotopomers of the oxygen molecule in the terrestrial atmosphere, 1602, '80'60, and '70'60. All lines passing a wavenumber dependent cutoff procedure (3.7 x lo-" cm-'/(molecule cm-') at 2000 cm-') are retained for the 1996 HITRAN database. Halfwidths as a function of the transition quantum numbers are determined from the available experimental measurements. Explicit expressions are obtained relating line intensities to the transition-moment squared, the vibrational band intensity, and the electronic-vibrational Einstein-A coefficient. The statistical degeneracy factors are presented and misuse of these factors in previous works is explained. Finally, band-by-band comparisons between the new calculations and the data from the previous HITRAN database are made. 0 1998 Elsevier Science Ltd. All rights reserved
TL;DR: In this paper, a general formulation of the multi-level rotation-vibrational non-LTE problem for a mixture of radiating molecular gases in a planetary atmosphere, treating explicitly the coupling of molecular energy levels by collisionally induced energy transfer processes and by band overlap, is given.
Abstract: A general formulation is given of the multi-level rotation–vibrational non-LTE problem for a mixture of radiating molecular gases in a planetary atmosphere, treating explicitly the coupling of molecular energy levels by collisionally induced energy transfer processes and by band overlap. Various limiting cases of non-LTE effects are discussed. Three techniques—lambda iteration, matrix and accelerated lambda iteration—which are used to solve these problem are discussed and compared. In the case of the CO 2 non-LTE problem in the Earth's atmosphere, it is demonstrated that accelerated lambda iteration is far superior to the other algorithms in minimizing computer time and storage and in converging much more rapidly; moreover the convergence rate is insensitive to the initial population estimates and to wide range of variation in the model input parameters. Accelerated lambda iteration therefore makes possible the calculation of much larger and more physically complete atmospheric and molecular models.
TL;DR: In this article, an airborne version of the POLDER (POLarization and Directionality of the Earth's Reflectances) instrument was designed to measure the bidirectional total and polarized reflectances of the solar light scattered by a cloud.
Abstract: During the EUCREX’94 (EUropean Cloud Radiation EXperiment 1994) campaign, observations of bidirectional reflected solar light above cirrus clouds off Brittany coast were collected with an airborne version of the POLDER (POLarization and Directionality of the Earth’s Reflectances) instrument. This instrument was designed to measure the bidirectional total and polarized reflectances of the solar light scattered by a cloud. The polarization measurements provide a very good signature of the water phase (liquid or ice) in the observed cloud. A more precise analysis of the behaviour of the polarized reflectances shows that it is highly sensitive to the shape of the cirrus cloud ice crystals for scattering angles ranging between 60° and 110°. One sequence of the POLDER images collected during EUCREX’94 pointed out the presence of hexagonal plates with aspect ratio equal to 0.1, whereas the analysis of an another sequence of images collected during the same campaign clearly shows a specular reflection of the solar light corresponding to the presence of horizontally oriented prismatic ice crystals in the cloud.
TL;DR: In this article, the authors present a new algorithm based on the discrete-ordinates method for the calculation of radiative transfer in three-dimensional, gray participating media of complex geometry.
Abstract: This paper presents a new algorithm based on the discrete-ordinates method for the calculation of radiative transfer in three-dimensional, gray participating media of complex geometry. The key feature of the new technique is the utilization of general characteristic equations which replace the classical spatial differencing schemes. These equations result from the formal integration of the radiative transfer equation followed by an averaging procedure on the surfaces. This feature enables the use of tetrahedral grids which can be fitted to any geometrical enclosure. Furthermore, the new algorithm does not generate the numerical oscillations and negative intensities that can be encountered with the traditional method. The method uses the techniques of recognition of neighboring cells. It is directly compatible with the solution of the conservation equations by finite element techniques. This paper is a sequel to a previous paper recently published by the same authors on two-dimensional cases. An assessment of the method is given by comparing the results for simple cases with those obtained by other authors. Application is then made to more complicated cases. The method is proved to be general and accurate.
TL;DR: In this article, the role of the intermolecular potential in the pressure broadening of water perturbed by nitrogen and oxygen is studied using a complex version of Robert-Bonamy theory.
Abstract: Using a complex version of Robert–Bonamy theory (CRBF), the role of the intermolecular potential in the pressure broadening of water perturbed by nitrogen and oxygen is studied. Investigation focuses on questions surrounding the convergence of calculated line widths, i.e., (i) why certain spectral lines are more sensitive than others to short-range interactions, and (ii) whether converged calculations containing short-range interactions represent an improvement over other treatments. Comparison with a large number of experimentally determined halfwidths and line shifts in the (301)←(000) and (221)←(000) bands is provided. It is found that the atom–atom component of the intermolecular potential plays an important role in determining the halfwidth and line shift. To obtain good agreement with measurement, the atom–atom potential needs to be expanded to at least eighth order for all water vapor transitions broadened by oxygen and many broadened by nitrogen.
TL;DR: In this paper, a singular value decomposition (SVD) is used to transform very large monochromatic look-up tables of optical depths into a compressed representation that is approximately 73 times smaller.
Abstract: We present a new technique for the fast computation of near-monochromatic atmospheric transmittances in the infrared, utilizing compressed look-up tables, that is well suited for nadir viewing satellite and airplane observations. The algorithm is very simple to use in radiative transfer codes and is easily adapted to provide analytic Jacobians of radiances. A Singular Value Decomposition (SVD) is used to transform very large monochromatic look-up tables of optical depths into a compressed representation that is approximately 73 times smaller. Temperature and pressure interpolations are performed in the compressed representation, resulting in significant savings in computation times. The resulting transmittances are as accurate as those computed with a line-by-line algorithm.
TL;DR: Using synchrotron radiation as a continuum light source, this article measured the absolute photoabsorption cross sections of OCS with a spectral bandwidth (FWHM) of 0.6
Abstract: Using synchrotron radiation as a continuum light source, we have measured the absolute photoabsorption cross sections of OCS with a spectral bandwidth (FWHM) of 0.6 A. The absorption cross sections of OCS have been measured from 2000 to 2600 A at temperatures of 370, 295 and 170 K, respectively. Many hot bands are observed in the 2150–2600 A region. Significant temperature effects on the absorption cross sections are clearly observed in the wavelength region longer than 2240 A.
TL;DR: In this article, the authors compute light scattering by stochastically deformed spheres using a volume integral equation formalism and find that spheroid is a much better approximation than a sphere, particularly in the case of linear polarization.
Abstract: We compute light scattering by stochastically deformed spheres using a volume integral equation formalism. For computational reasons we are restricted to volume equivalent size parameters less than about eight for a collection of particles in random orientation. To see how well light scattering by rough particles can be approximated by using equal volume spheroids (computed by the T-matrix method) or by spheres (computed using Mie theory), we compute standard deviations between the different models for the intensity and linear polarization. As expected, a spheroid is a much better approximation than a sphere, particularly in the case of linear polarization. Only as an exercise we assume a power law distribution of particle sizes and compute light scattering by our realizations the intensity shows a distinct opposition spike close to backscattering and linear polarization is qualitatively astonishingly close to that observed for atmosphere less solar system objects.
TL;DR: In this paper, the effects of multiple scattering by non-spherical hydrometeors were investigated in the microwave region and the model developed uses the full Stokes vector to include the effect of cross-polarization terms between all Stokes components, which are important when the scattering of nonspherical particles is considered.
Abstract: We present the results of radiative transfer calculations in the microwave region focussing on the effects of multiple scattering by non-spherical hydrometeors. The use of microwave frequencies, e.g. 37 GHz, leads to a size parameter of 1.5 for raindrops with 4 mm diameter and requires an exact scattering solution rather than Rayleigh approximation. The distortion of raindrop shapes from the spherical geometry becomes significant and has to be taken into account when the scattering properties are calculated. The model developed uses the full Stokes vector to include the effects of cross-polarization terms between all Stokes components, which are important when the scattering of non-spherical particles is considered. The one-dimensional microwave radiative transfer model is based on the successive order of scattering method and assumes azimuthal symmetry. The shape of the hydrometeors is approximated by rotational symmetric ellipsoids with a size dependent aspect ratio. These particles have a fixed orientation with their rotational axis aligned along the vertical. Results for non-spherical and spherical scattering are presented. The differences between both methods, leading to 15 K change in the polarization difference depending on rain rate, frequency and viewing angle, are discussed.
TL;DR: In this article, a novel radiative transfer model for a scattering layer in a plane-parallel thermally emitting atmosphere is described, which combines a single-scatter method with the standard Eddington's second approximation technique, which is required for higher order scattering.
Abstract: A novel radiative transfer model for a scattering layer in a plane-parallel thermally emitting atmosphere is described. The model is designed for computing radiances in iterative remote-sensing methods where computational efficiency is of utmost importance. The model combines a single-scatter method with the standard Eddington’s second approximation technique, which is required for higher-order scattering. The single-scattering model uses tabulated scattering properties. The accuracy of the hybrid model, relative to an exact doubling-adding model, is compared with three other approximate methods (nonscattering, single-scattering, and Eddington). Brightness temperature errors for simulated ice and water clouds are shown for various particle size distributions in both microwave (1–50 cm-1) and infrared (300–3000 cm-1) parts of the spectrum. As indicated by a root-mean-square measure of brightness temperature error over outgoing directions, the hybrid model is a significant improvement over the standard Eddington model in the regions of the infrared where scattering is important. Computer source code (written in FORTRAN) for implementing the hybrid scattering model is available from the authors.
TL;DR: In this paper, the vertical mixing ratio profiles of four relatively long-lives gases, HCN, C2H2, CO, and CO, were retrieved from 0.01/cm resolution infrared solar occultation spectra recorded between latitudes of 5.3degN and 31.4degN.
Abstract: Vertical mixing ratio profiles of four relatively long-lives gases, HCN, C2H2, CO, and C2H6, have been retrieved from 0.01/cm resolution infrared solar occultation spectra recorded between latitudes of 5.3degN and 31.4degN. The observations were obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Science (ATLAS) 3 shuttle flight, 3-12 November 1994. Elevated mixing ratios below the tropopause were measured for these gases during several of the occultations. The positive correlations obtained between the simultaneously measured mixing ratios suggest that the enhancements are likely the result of surface emissions, most likely biomass burning and/or urban industrial activities, followed by common injection via deep convective transport of the gases to the upper troposphere. The elevated levels of HCN may account for at least part of the "missing NO," in the upper troposphere. Comparisons of the observations with values measured during a recent aircraft campaign are presented.
TL;DR: In this article, the authors apply the discrete dipole approximation (DDA) to estimate the radiation pressure cross section for fluencyy aggregates by computing the asymmetry parameter and the cross sections for extinction and scattering.
Abstract: We apply the discrete dipole approximation (DDA) to estimate the radiation pressure cross section for flu⁄y aggregates by computing the asymmetry parameter and the cross sections for extinction and scattering. The ballistic particle—cluster aggregate and the ballistic cluster—cluster aggregate consisting of either dielectric or absorbing material are considered to represent naturally existing aggregates. We show that the asymmetry parameter perpendicular to the direction of wave propagation is maximized where the wavelength is comparable to the aggregate size, which may be characterized by the area-equivalent radius or the radius of gyration rather than the volume-equivalent radius. The asymmetry parameter for the aggregate depends on the morphology of the particle, but not on the constituent material. Therefore, the dependence of the radiation pressure cross section on the material composition arises mainly from that of the extinction and scattering cross sections, in other words, the single-scattering albedo. We find that aggregates consisting of high-albedo material show a large deviation of radiation pressure from the direction of incident radiation. When the aggregates are illuminated by blackbody radiation, the deviation of the radiation pressure increases with increasing temperature of the blackbody. Since the parallel component of the radiation pressure cross section for the aggregates is smaller than that for the volume-equivalent spheres at the size parameter close to unity, the Planck-mean radiation pressure cross section for the aggregates having radius comparable to the e⁄ective wavelength of radiation shows a lower value, compared with the volume-equiva- lent sphere. Consequently, the slope of the radiation pressure force per mass of the particle as a function of particle mass shows a lower maximum for the aggregates than for compact spherical particles. ( 1998 Elsevier Science Ltd. All rights reserved.
TL;DR: The 1996 HITRAN update of HNO 3 absorption parameters is reviewed, for both discrete lines and cross-sections, as well as ongoing studies and needs for further improvements.
Abstract: The 1996 HITRAN update of HNO 3 absorption parameters is reviewed, for both discrete lines and cross-sections. Recent results not incorporated into the HITRAN database are described, as well as ongoing studies and needs for further improvements.
TL;DR: A computer code is implemented which can handle any homogeneous, starshaped particle and general T -matrix expressions are presented in a form suitable for computer code generation.
Abstract: The T -matrix method has almost exclusively been applied to rotationally symmetric particles. We have implemented a computer code which can handle any homogeneous, starshaped particle. General T -matrix expressions are presented in a form suitable for computer code generation. Simple scattering problems are solved in order to show the capability of this method.
TL;DR: In this article, a method for the calculation of longwave clear sky fluxes and cooling rates based on the GENLN2 line-by-line radiative transfer code has been implemented, and studies have been carried out of the sensitivity and response of the outgoing planetary radiation to changes in atmospheric composition.
Abstract: Recent studies have highlighted the important contribution made by the far i.r. component of the water vapour spectrum to present-day greenhouse forcing, and the possible influence of this region upon future climate. In order to further assess these findings at high spectral resolution a method allowing the calculation of longwave clear sky fluxes and cooling rates based on the GENLN2 line-by-line radiative transfer code has been implemented, and studies have been carried out of the sensitivity and response of the outgoing planetary radiation to changes in atmospheric composition. Comparisons with other line-by-line model show typical cooling rate agreement of within 0.05 K day −1 at all pressure levels. Taking two model atmospheres representative of tropical (TRP) and sub-arctic winter (SAW) conditions, several experiments have been performed to assess both the present-day greenhouse effect, and the impact of perturbations in carbon dioxide and water vapour amounts on the greenhouse trapping of each atmosphere. The results reinforce the importance of the far i.r. with, for the present-day conditions, one third and one quarter of the total absolute greenhouse forcing calculated to occur in this region for the SAW and TRP atmospheres respectively. The sensitivity of the normalised greenhouse effect to water vapour concentrations is greatest in the far i.r. for the SAW atmosphere, and in the window region for the TRP; this sensitivity differing most between atmospheres in the far i.r. The sensitivity to vertical variations in water vapour perturbation shows a peak response located at mid-tropospheric levels within the window region for the TRP case, and within the far i.r. at upper tropospheric levels for the SAW atmosphere. The carbon dioxide perturbation experiments indicate the increasingly important role played by the weaker carbon dioxide bands as concentrations increase, and provide a further illustration of the fallacy of the suggestion of a `CO 2 saturated' atmosphere.
TL;DR: A new method will be presented which offers a much simpler way to derive a T-matrix without running into the problems of the Rayleigh hypothesis, achieved by a generalization of the Separation of Variables Method (SVM) which uses the differential formulation of the scattering process.
Abstract: During the last years, the T-matrix approach based on the Extended Boundary Condition Method (EBCM) has become a powerful technique for solving the problem of plane wave scattering by non-spherical particles. It can be applied to different geometries and to large size parameters. For certain scattering configurations this method is able to bridge the gap between the resonance region and the geometric optics approximation. Despite these advantages it still remains a difficult method for practitioners. It is accompanied by loss of simplicity in concept and execution caused by the formulation in terms of integrals and related problems like the formulation of the non-local EBC, and the open question if it suffers from a restricted range of applicability of the Rayleigh hypothesis. In this paper, a new method will be presented which offers a much simpler way to derive a T-matrix without running into these problems. This is achieved by a generalization of the Separation of Variables Method (SVM) which uses the differential formulation of the scattering process. In this way, we are able to remove the mistake that SVM can be applied only if the boundary surface of the scatterer coincides with a constant coordinate line. Additional advantages of this approach are the possibility to consolidate different methods into a common mathematical body, thus allowing a better estimation of the accuracy of different numerical techniques, and the possibility to find an answer to the problem of the Rayleigh hypothesis. To formulate this new approach the method of lines (MoL) is used as a starting point. The MoL is a mathematical tool for solving partial differential equations, and it has been applied very successfully in guided wave theories. It also forms the mathematical basis of the Discretized Mie-formalism (DMF) which has been recently developed for plane wave scattering. With this contribution, there will be discussed interesting new aspects of the MoL.