Random Band Model Research Articles

Practical approaches for evaluating radiative heat from high pressure hydrogen flame

As the construction of hydrogen stations and other hydrogen-related facilities progresses, it becomes increasingly crucial for safety designs to account for scenarios where leaked hydrogen might ignite. Since a hydrogen flame is usually invisible, detection must rely on radiative heat or temperature. While it is possible to predict accurate radiative heat flux from a high pressure hydrogen jet flame through detailed numerical calculations of hydrogen combustion with its radiation, the objective of this study is to provide a simpler and more accurate prediction method. Previous experimental data of radiative heat flux, Qr from high pressure hydrogen jet flames were compiled, and a simple experimental equation Qr=1463.3(Lo/Lf)−2.32 was derived, where Lf and Lo represent the flame length and the distance perpendicular to the flame axis from the midpoint of the flame length to the observer, respectively. Radiative heat fluxes were computed through detailed numerical simulations using three types of water vapor radiation models: Goody's narrow random band model, the exponential broad band model by Edward and Elsasser's narrow regular band model. The temperature and water vapor partial pressure distributions obtained from numerical simulations were used as input conditions. The results were found to be in good agreement with the experimental equation. Moreover, a simple diagram representing the radiative heat flux from a hydrogen flame was derived using the method of cylinder-like approximation. The results of this study show that if the hydrogen pressure and leakage aperture diameter are given, the radiative heat flux at a certain distance can be predicted with high accuracy. Additionally, the average value of emissivity for the hydrogen diffusion flame was found to be on the order of 0.03.

Machine Learning Study on the Flat-Band States Constructed by Molecular-Orbital Representation with Randomness

We study the characteristic probability density distribution of random flat band models by machine learning. The models considered here are constructed on the basis of the molecular-orbital representation, which guarantees the existence of the macroscopically degenerate zero-energy modes even in the presence of randomness. We find that flat band states are successfully distinguished from conventional extended and localized states, indicating the characteristic feature of the flat band states. We also find that the flat band states can be detected when the target data are defined in the different lattice from the training data, which implies the universal feature of the flat band states constructed by the molecular-orbital representation.

Updated radiative forcing estimates of 65 halocarbons and nonmethane hydrocarbons

The direct radiative forcing of 65 chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers, halons, iodoalkanes, chloroalkanes, bromoalkanes, perfluorocarbons and nonmethane hydrocarbons has been evaluated using a consistent set of infrared absorption cross sections. For the radiative transfer models, both line‐by‐line and random band model approaches were employed for each gas. The line‐by‐line model was first validated against measurements taken by the Airborne Research Interferometer Evaluation System (ARIES) of the U.K. Meteorological Office; the computed spectrally integrated radiance of agreed to within 2% with experimental measurements. Three model atmospheres, derived from a three‐dimensional climatology, were used in the radiative forcing calculations to more accurately represent hemispheric differences in water vapor, ozone concentrations, and cloud cover. Instantaneous, clear‐sky radiative forcing values calculated by the line‐by‐line and band models were in close agreement. The band model values were subsequently modified to ensure exact agreement with the line‐by‐line model values. Calibrated band model radiative forcing values, for atmospheric profiles with clouds and using stratospheric adjustment, are reported and compared with previous literature values. Fourteen of the 65 molecules have forcings that differ by more than 15% from those in the World Meteorological Organization [1999] compilation. Eleven of the molecules have not been reported previously. The 65‐molecule data set reported here is the most comprehensive and consistent database yet available to evaluate the relative impact of halocarbons and hydrocarbons on climate change.

Methane heating rates in outer planet atmospheres

We have reviewed and expanded the techniques for calculating the heating rates of CH 4 near-i.r. bands (3.3, 2.3 and 1.7 μm) for conditions relevant to the atmospheres of the outer planets. We consider all pressures below 100 mbar and temperatures from 77 to 300 K. We find that using the correlated- k method, the heating rates of the stronger band, 3.3 μm band, at all pressures and the heating rates for the other two bands at pressures below 0.1 mbar can be accurately calculated. We also find that the application of the general random band models which depend on the line listings is not appropriate to these three bands.

Spectral parameters of self- and hydrogen-broadened methane from 2000 to 9500 cm -1 for remote sounding of the atmosphere of jupiter

Long-pathlength self- and H 2-broadened absorption spectra of CH 4 have been recorded from 2000 to 9500 cm -1 at a resolution of 0.25 cm -1. Thesespectra were obtained for a wide range of conditions relevant to the atmosphere of Jupiter, including nominal temperatures of 190, 240, and 296 K, pathlenghts from 64 to 512 m, and pressures from 0.2 to 700 torr, giving CH 4 column abundances from 0.016 to 530 m-amagat. A series of molecular band models were fitted to these spectra at 10 cm -1 resolution, showingthat the Goody and Malkmus random band models with the Voigt lineshape provided the best fits to the data. The Goody-Voigt model was subsequently used to calculate the level in the Jovian atmosphere that will be sounded by observations of CH 4 absorption, and estimates were made of the accuracy to be expected if this model were used to retrieve atmospheric parameters.

Longwave band model for thermal radiation in climate studies

To accurately simulate the present Earth climate requires an atmospheric longwave radiation model whose computed fluxes agree to within ±1% of the only presently available standard, line by line (LBL) calculations. This standard derives from the agreement to within ±1% of various LBL calculations (Luther et al., 1988). To model potential future climate change requires an atmospheric longwave radiation model that can easily incorporate many trace gases. To meet these requirements, a longwave band model of 100 cm−1 resolution is presented. Random band model transmissions are modified to account for overabsorption compared to LBL calculations, with empirical coefficients chosen to give good agreement with LBL spectral fluxes. The longwave band model (LWBM) integrated fluxes agree to within ±1% of LBL fluxes, while heating rates agree to within ±5%. The LWBM is used in the National Center for Atmospheric Research Community Climate Model Version 1 to compute longwave radiation. It is demonstrated that by not including minor bands of CO2 and O3, other trace gases (CH4, N2O, CFCl3, CF2Cl2), or nonblack surface emissivity effects results in a significant bias in tropical clear‐sky outgoing longwave radiation of 8–10 W m−2 over oceans and up to 15 W m−2 over sandy deserts.

The correlated-k coefficients calculated by random band models

The correlated- k coefficient for the cumulative distribution of the absorption coefficient in random band models is calculated with a computationally efficient algorithm based on a numerical inverse Laplace transform. A scaling transformation is introduced to partially eliminate the ill-conditioned behavior around the singularity point. In the region very close to the singularity, an analytic expression for the k coefficient derived for the Malkmus model is used to match the whole solution. The algorithm yields accurate k coefficients with a maximum error for a few percent. When applied to the random band model with an S -1-β-tailed line intensity distribution and a Voigt line profile, the algorithm yields a maximum error in the escape function of < 3% in comparison with line-by-line integrations. The algorithm is sufficiently general to be applicable to a variety of radiative transfer problems in planetary atmospheres.

Radiative Cooling Calculated by Random Band Models with S-1-βTailed Distribution

Abstract Random band models with S-l-u tailed distribution for line intensity are proposed for both the Lorentz lineprofile and an approximate Voigt line profile suggested by Zhu. Such a distribution for the weak line intensityis more realistic than a Goody or Malkmus distribution. The transmission functions for the Goody and Malkmusrandom models can be derived as two special cases (j3 = -I and j3 = 0) of the present formulation, which isexpressed in the form of the hypergeometric function. It is shown that if j3 0.2, the improvement to thecalculations using the tailed distribution is as great as using the Malkmus rather than the Goody model.The transmission function for the Voigt line profile is applied to the calculations of Cot 15 pm band coolingrate in the middle atmosphere. The results show that by choosing more appropriate distribution in randomband models, the accuracy in cooling rate can be significantly improved, while the computation effort requiredis comparable in magnitude to the corresponding...

Parameterization of the radiative flux divergence in the 9.6 μm O 3 band

A parameterization of the cooling rate of the Earth's atmosphere in the height region of approximately 20–75 km due to radiation transfer in the 9.6 μm O 3 band is proposed. A general random band model is used to calculate the radiation transmission. The parameterization takes into consideration a peculiar feature of the radiative transfer—the height step increases with growing distance from the level for which cooling is calculated. A simple method of accounting for the variation of the vertical profile of the absorbing gas is proposed and utilized. The procedure proposed is multiparametric: 22 parameters are prescribed for calculating cooling at a given level. The procedure can be recommended for calculating radiative cooling for any temperature and ozone profile not having a small- or meso-scale structure. It can be used, in particular, for modelling of the middle atmospheric circulation.

Solar absorption by atmospheric water vapor: a comparison of radiation models

We have intercompared several different procedures for evaluating solar absorption by atmospheric water vapor, and in particular we have employed a random band model as a diagnostic tool for assessing approximations which are inherent in existing parameterizations. We reaffirm McDonald's (1960) conclusion as to the importance of the 0.72 and 0.81 μm water vapor absorption bands, and we find that the Goody random band model and the Lacis-Hansen empirical parameterization produce comparable tropospheric heating rates. This agreement does not extend to the stratosphere. for which water vapor amounts lie outside the intended range of applicability of the Lacis-Hansen parameterization. But when diurnal averaging is taken into account, the disagreement is reduced. We further present what is in effect a two-parameter extension of the Lacis-Hansen parameterization. DOI: 10.1111/j.1600-0889.1985.tb00055.x

Two-parameter method of summing equivalent spectral linewidths in the Curtis-Goodson approximation

An expression is found, within the framework of a random band model, for the spectral-line intensity distribution density in application to the problem of IR radiation transfer in an inhomogeneous molecular-gas volume.

Nitric-acid band intensities and band-model parameters from 610 to 1760 cm^−1

A set of 59 spectra of pure nitric acid was obtained at temperatures ranging from 236 to 294 K using path lengths from 10 to 50 cm and pressures from 0.05 to 1.1 Torr. No strong temperature dependencies were observed over the range of our measurements. Absorption coefficients and mean line-spacing parameters were determined at each 1-cm−1 interval in the three strong bands at 5.9, 7.5, and 1.3 μm by using a two-parameter random-band model. The resulting intensities for these bands are 1530 ± 100, 1383 ± 70, and 692 ± 35 cm−2 amagat−1, respectively. In addition, the absorption coefficients were determined in the three weak bands at 8.3, 13.2, and 15.5 μm. The band intensities derived are 44 ± 4, 45 ± 4, and 50 ± 5 cm−2 amagat−1, respectively.

Propane absorption band intensities and band model parameters from 680 to 1580cm -1 at 296 and 200 K

Band intensities and profiles have been measured for the propane absorption bands from 680 to 1580cm -1 at 296 and 200 K. This work was stimulated by the discovery of several propane bands in the spectrum of Titan by the Voyager 1 spacecraft. The low temperature laboratory data show that the bands become narrower and the Q branches of the bands somewhat stronger than they are at room temperature. Random band model parameters were determined over the entire region from the 42 spectra obtained at room temperature.

Real line strength distributions for random band models

An improved random band-model method, which takes into account the real line-strength distribution, is presented. This model is useful for low resolution, infrared observational data of the outer solar system.

Band model analysis of the H 2O 2ν6(b) band

A Mayer-Goody random band model with a Voigt line profile is used to derive interval absorption coefficients, mean line spacings, and pressure-broadening coefficients for the ν 6(b) H 2O 2 band centered at 1265 cm −1 at 285°K.

Comparison of band model and integrated line-by-line synthetic spectra for methane in the 2.3 μm region

The 2.3 μm spectral region of methane can be used to retrieve cloud properties of planetary spectra, provided parameters for the methane spectrum are known. Two standard techniques for calculating absorption spectra in this region are compared here. A Voigt profile Mayer-Goody random band model is applied, using coefficients empirically fitted by Fink et al. to CH 4 spectra recorded with high absorping amounts at 10 cm −1 resolution. Calculation of the absorption is also done with a line-by-line direct integration method for the same gas conditions using molecular parameters obtained by combining an older unpublished list of observed positions and estimated line strengths (derived from 0.04 cm −1 resolution data) with quantum assignments from the literature. The molecular parameters have been evaluated for the 4180–4590 cm −1 region by comparing new laboratory spectra with 0.01 cm −1 resolution recorded at 296 and 153K with synthetic spectra calculated at the same conditions. The deficiencies of the molecular parameters and random band coefficients for this spectral region of CH 4 are then discussed qualitatively and demonstrated by comparing 10 cm −1 resolution synthetic spectra calculated by both methods for the same gas conditions at 296, 153, and 55 K. Curves of growth of the total equivalent width are calculated at 296 and 55K for a pathlength of 50 cm and pressures up to 10 atm. Changing the mean line spacing in the band model gives better agreement between the spectra calculated by the two techniques at low gas temperatures. The required multiplier has been determined for the mean line spacing for pressures from 10 −6 to 10 −1 atm at 55, 100, and 150 K.

An accurate representation of the transmission functions of the H 2O and CO 2 infrared bands

A simple but accurate formula is given that describes the characteristics of the transmission function of gaseous absorption bands which are not well described by the Mayer-Goody random band model (e.g. the effect of the difference of line-intensity distribution between wavenumber intervals). The temperature dependence of the transmission function is also well described. The parameters for our model have been determined for infrared bands of water vapor and carbon dioxide by fitting values of transmittance calculated from line parameter data of McClatchey et al. The results have been compared with experimental measurements.

Band model calculations for CFCl 3 in the 8–12 μm region

A Goody random band model with a Voigt line profile is used to calculate the band absorption of CFCl 3 at various pressures at room and statospheric (216°K) temperatures. Absorption coefficients and line spacings are computed.

Triton - A satellite with an atmosphere

view Abstract Citations (57) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Triton: a satellite with an atmosphere. Cruikshank, D. P. ; Silvaggio, P. M. Abstract A low-resolution infrared spectrum of Triton in the region 1.4-2.6 microns shows a broad absorption at 2.3 microns which is attributed to gaseous methane. The computed surface partial pressure of CH4, based on a random band model extrapolation of new laboratory spectra, is (1 + or - 0.5) times 10 to the -4th bars, a value consistent with the calculated vapor pressure of methane gas above methane ice at the expected temperature of Triton. There is, however, no compelling evidence for the presence of solid CH4 on the satellite's surface. Publication: The Astrophysical Journal Pub Date: November 1979 DOI: 10.1086/157465 Bibcode: 1979ApJ...233.1016C Keywords: Infrared Astronomy; Infrared Spectra; Natural Satellites; Neptune (Planet); Planetary Atmospheres; Absorption; Methane; Partial Pressure; Reflectance; Spectrophotometry; NEPTUNE; SATELLITES; TRITON; INFRARED; SPECTRUM; ICE; ATMOSPHERE; ABSORPTION; METHANE; VAPOR PRESSURE; MODELS; DATA; TELESCOPIC OBSERVATIONS; EQUIPMENT; SURFACE; SPECTROPHOTOMETRY; WAVELENGTHS; ANALYSIS; ALBEDO; GASES; Lunar and Planetary Exploration; Satellites of Neptune; Infrared Spectra:Neptune Satellites full text sources ADS |

A Perturbative Treatment of Aerosol Scattering of Infrared Radiation

Calculations of long-wave atmospheric heating and cooling rates using the rate equations of Rodgers and Walshaw (1966) with the Malkmus (1967) random band model are presented. A perturbation scheme is developed for the inclusion of aerosol scattering effects in the numerical calculation. Unlike the flux differencing method for calculating long-wave heating and cooling rates, this scheme allows aerosol effects to be included in a simple manner with only a small additional use of computer time. The calculations indicate good agreement with those of previous investigators and demonstrate the expected equivalence of the flux-differencing method and the flux-divergence equation of Rodgers and Walshaw (1966), even at stratospheric altitudes. It is found that aerosols lead to a net heating in the lower troposphere due to infrared scattering and absorption.