The regional climate model RegCM 4.9 is deployed on the computer cluster to simulate the region centered in the Lower Volga region, including the Northern Black Sea region and Western Kazakhstan. We present the results of a comparative analysis of the dynamics of small-scale vortex structures in models with vertical hydrostatic equilibrium of the atmosphere and in models without hydrostatic equilibrium based on the full 3D RegCM core. The quality of approximate methods for calculating the radiative transfer in the atmosphere for climate modeling is discussed. The use of the RRTM_LWradiation scheme in RegCM provides an uncertainty well below 1 percent due to the continuum absorption by water vapor in the upward and downward radiation fluxes.
Modern models of water vapor continuum are compared in the atmospheric transparency windows of 3-5 and 8-12 μm. The longwave radiative fluxes at the top and bottom of cloudless atmosphere are calculated. The differences in the upward and downward radiative fluxes caused by uncertainties in water vapor continuum models are estimated.
Water vapor is an important greenhouse gas. The atmospheric water vapor content is monitored by remote methods, which require accurate spectroscopic information about H2O absorption line parameters. The problems of accuracy of accounting the selective water vapor absorption in the simulation of atmospheric transfer of solar radiation are considered in this work. The atmospheric spectra are simulated using different versions of spectroscopic databases of H2O absorption line parameters and compared with the solar spectra measured by a ground-based Fourier transform spectrometer. The total column (TC) water vapor is retrieved from the solar spectra measured. The effect of the differences in absorption line parameters in modern spectroscopic databases on the results of retrieval of the TC water vapor from high-resolution spectra is estimated.
The atmospheric solar spectra are simulated using new data on methane absorption lines. A comparison of the simulated spectra with the atmospheric spectra, measured by a ground-based Fourier spectrometer in the methane absorption bands in the near-infrared spectral region, is carried out. The atmospheric column-averaged volume mixing ratio of methane is retrieved from the measured spectra.
The atmospheric radiative fluxes and cloud radiative forcing are simulated with use of different models of water vapor continuum absorption and cloud optical depths. The effects of radiative heating and cooling of the cirrus cloudiness are analysed. A contribution of water vapor continuum absorption to the atmospheric radiative transfer is estimated. It is shown that sign of cloud radiative effect depends on choice of water vapor continuum model.
Estimations of the effect of modern ozone absorption cros-ssections data on calculation of the atmospheric transmission and fluxes, measured using Sun photometers in the UV spectral region, are made. The ozone absorption cross-sections, often used in radiative codes, and new data of Serdyuchenko et al. are considered.
The longwave radiative fluxes were simulated using different water vapor continuum models for meteorological conditions of Tomsk and Volgograd. The atmosphere with various temperatures, water vapor contents and optical depths of cirrus clouds was considered. The contribution of uncertainties in the continuum models to simulation of downward and upward longwave fluxes is estimated.
The atmospheric solar spectra are calculated using different spectroscopic databases of H2O absorption line parameters in the temperature and humidity range observed in the mid-latitudes. A comparison of the simulated spectra and measured high-resolution atmospheric spectra in the near-infrared water vapor bands, is carried out. It is shown that the values of H2O atmospheric column, retrieved using different modern spectroscopic databases may vary by more than 3%.
The estimation of errors in the longwave radiative fluxes simulation due to uncertainties in our knowledge of selective and continuum molecular absorption is presented. Modern models of the water vapour continuum absorption and different versions of the HITRAN spectroscopic database (2004, 2008, 2012) are used. It is shown that at present, the major source of the calculation errors in the longwave fluxes at cloudless atmosphere is still an uncertainty in the water vapour continuum absorption coefficients, while the contribution of line parameters’ errors to the simulation is relatively small.
KEYWORDS: Absorption, Spectroscopy, Molecules, Data modeling, Databases, Atmospheric chemistry, Temperature metrology, Thermodynamics, Data acquisition, Oxygen
Our research into generation of a set of absorption cross sections of atmospheric molecules is reviewed briefly. Particular emphasis is placed on a description of a software toolkit for building information objects that characterize molecules and weakly bound molecular complexes, an application that provides the import and export of the absorption cross sections and representation of metadata and ontolology of information resources collected in a set.
We had been conducting the results of surface spectroscopy of radiometric measurements of aerosol and water vapor in the atmosphere of Volgograd for period since July 2011 for September 2013, applying a SPM photometer. Volgograd is a city in the southeast of the European part of Russia, the administrative center of the Volgograd region. It's located in latitude 48.42 N, longitude 44.28 Е and altitude 156 meters above sea level. Spectral aerosol optical depth, the Angstrom wavelength exponent and general water vapor content were computed with the help of the data having been written on sun photometer through the direct measuring of sun radiance. The mean values of aerosol optical depth at 0.440 μm, water vapor the atmospheric column and the Angstrom wavelength exponent during the indicated period of time were computed to be 0.20 ± 0.12, 1.97 ±0.67 g/cm2 and 1.58 ± 0.71 accordingly. The maximal and minimal values of aerosol optical depth were recorded in August 2013 and in July 2013. The general water vapor content in the vertical atmospheric column was recorded in August 2013 and in November 2012). Using the method of the least squares the Angstrom exponent in the spectral measurements from 0.440 to 0.870 μm was computed.
In the work an analysis of possible errors of the longwave radiative fluxes calculation due to spectroscopic uncertainties
of HITRAN2004 database lines parameters and continuum models is carried out. Upper estimations of the fluxes
calculation errors are founded. The errors are 0.2% for downward and 0.25% for upward fluxes. It is shown that the
uncertainties of water vapor continual absorption may cause the fluxes error more then 1%, that exceeds the line
parameters error. A comparison of the radiative fluxes calculated with different continuum models used in radiative
codes is made.
The method of time-resolved photoacoustic spectroscopy is applied to study the weak aerosol absorption of shortwave radiation in the atmospheric air. Using synchronous measurements of aerosol light absorption coefficients by a pulsed photoacoustic spectrometer and mass concentration of black carbon by an Aethalometer, we determine the values of the efficiency of aerosol light absorption in the atmospheric air in the shortwave spectral range for three wavelengths: (0.532 µm)=(5.49±3.57)m2 g–1, (0.694 µm)=(4.46±2.61)m2 g–1, and (1.064 µm)=(2.87±1.84)m2 g–1. The experimental results are approximated by the spectral dependence ()=3.1–0.92, where wavelength is expressed in micrometers. We discuss the calibration procedure for the pulsed photoacoustic spectrometer in studying the aerosol absorption.
Now one of the topical problems of atmospheric optics is the creation of effective methods of radiative transfer calculation in the aerosol-gaseous the earth atmosphere that provides a high speed, accuracy and engineering software. In this work, techniques of calculation and parameterization of molecular absorption characteristics, applied to solving the problem of the narrow-band and broadband laser beam propagation, are described. The analysis of errors of the spectroscopic information is performed and techniques of calculation of errors are described. It is believed that intensities and half-widths of spectral lines have systematic and random errors. Results of simulation of influence of temperature and atmospheric gas concentration variations of molecular absorption coefficients are presented. The method of calculation of mean and mean square deviations of molecular absorption characteristics is presented for the case, in which the limited statistical information about meteorological parameters of the atmosphere is used. The prognostic atmospheric model allowing correct optical characteristics of slant atmospheric paths based on the information about near-surface temperature and humidity of the air is offered.
At present some differences are observed between measured and calculated fluxes of solar radiation at the Earth’s surface. According to recent investigations these differences correlate with columnar water vapor. The results of calculation of the contribution of numerous weak absorption lines of water vapor, which usually are not taken into account as applied to atmospheric radiation problems, to the irradiance of the Earth’s surface and spectral brightness of sky are considered. Spatial-angular brightness was modeled in several spectral intervals of near IR and visible ranges at different vision directions and Sun positions. Irradiance of the Earth’s surface was estimated in the range of 4000-20000 cm-1 under different aerosol conditions. It was performed comparative calculations for the HITRAN2000k spectral lines database and Partridge-Schwenke data. The calculated results have shown that the neglect of the contribution of weak absorption lines of water vapor in the near IR and visible regions can lead to errors (to 2% in the 100 cm-1 intervals) in calculation of the diffuse radiation.
KEYWORDS: Atmospheric modeling, Atmospheric optics, Absorption, Scattering, Radiative transfer, Multiple scattering, Earth's atmosphere, Monte Carlo methods, Ocean optics, Control systems
The modern method for modeling selective gas absorption to solve problems of radiative transfer in the spatially inhomogeneous atmosphere is considered. The method is based on representation of the atmospheric transmission function as a series of exponential functions. This representation not only provides for high accuracy of calculations, but also proves to be efficient when considering multiple scattering.
Some peculiarities of the femtosecond laser radiation propagation through molecular resonant media are studied. Calculations of atmospheric transmission through the horizontal paths are also presented.
This paper generalizes the results of development of few- parameter models of transmittance, which provide both the needed accuracy close to that given by the LBL method and the high computational speed. Particular emphasis is placed on the latest advances connected with the Laplace transformation and presentation of the transmission function as exponential series.
The estimates of absorption of CO-, HF- and DF-lasers multifrequency radiation along extended atmospheric paths are presented in the paper. Peculiarities in the behavior of absorption characteristics depending on the path profile, spectrum of the laser emission, and meteorological conditions are analyzed. We also analyze the influence of thermal nonlinearity on the beam characteristics.
We present estimates of influence of refraction on gas throws concentration measure by trace gas analyzer. The used model of spatial distribution of gas concentrations is correspond to gas throws from pipe lines. The molecules of CH4 were considered as markers of such gas throw. Influence of refraction on parameters of collimated probing beam was shown to result mainly to its shift relatively receiver telescope.
The retrieval technique for sensing the columnar content of CO2 via differential solar transmission measurements in and out absorption bands is presented. The calibration procedure based on the line-by-line method is described. The k-distribution method is used for acceleration calculation. The multiwavelength Sun-photometer has six channels for measurements in and out the H2O, CO2, CH4 absorption bands. The interferometer filters are used for spectral selection with resolution (Delta) (lambda) /(lambda) approximately equals 0.01 - 0.02. The wavelengths are centered at 0.87, 0.94, 1.06, 2.06, 2.18, 2.32 micrometers. Errors of the columnar content retrieval connected with the parametrization of atmospheric transmittance and uncertainties of the spectroscopy information are analyzed. The correction of signal on the basis of the measurements of aerosol optical depth is described.
Peculiarities of pulsed industrial lasers propagation through the atmosphere when branch of the laser generation coincides with an atmospheric H2O absorption line are studied. Problems of DIAL sounding of atmospheric H2O by these laser are also discussed.
This report presents a new effective method which can be used to compute both the transmittance and the atmospheric radiation fluxes in the overlapping water vapor and carbon dioxide absorption bands.
The dialog package SAGDAM (sounding of atmospheric gases by differential absorption method) is intended for simulation of the potentialities of the DAS method for sounding water vapor and ozone on the vertical and slant directions with ground-based, airborne, and spaceborne lidars. Moreover, the package enables one to model the ground-based, airborne, and spaceborne systems for sounding the integral gas content by a long-path differential absorption method. The spectral range is near UV, visible, and infrared spectral ranges. The program calculates: a) vertical profiles of the absorption coefficients and transmittance of the gas under study and the foreign gases, as well as the transmittance of aerosol and Rayleigh atmosphere; b) spatially resolute error including random error and systematic error. The program enables one to determine the optimal pairs of wavelengths for sounding a gas in the specified altitude range and the minimum-detectable concentration of the gas under study (for the long-path method).
KEYWORDS: Absorption, Gases, Atmospheric modeling, Systems modeling, Computer programming, Interference (communication), Signal processing, Signal attenuation, Laser systems engineering, Transmittance
The dialog program LPM (long-path method) is intended for imitative modeling of the concentration gas analysis (H2O, CO2, O3, NH3, C2H4) with the path double-wave gas analyzer, equipped with two tunable CO2-lasers. Modeling is designed for four laser systems using the isotopes of CO2. While modeling the program provides: 1) the calculation of transmittance for a sounding path at wavelengths 'on-line' and 'off-line'; 2) the calculation of atmospheric signals at wavelengths 'on-line' and 'off-line'; 3) the distortion of a signal with a random number for imitation of measuring noise; 4) the calculation of gas concentration from the inverse problem while imitating the sounding of a single gas; 5) the calculation of concentration of several gases (up to five gases) by using the simultaneous signal processing for several pairs of wavelengths (imitation of sounding of several gases). In addition, the program determines: i) optimal pairs of wavelengths; ii) the gas concentration reconstruction error from the sounding data, including the measuring error and the systematic error.
In deciding the laser type for operation in the atmosphere, one should adopt the generation frequencies which coincide with atmospheric windows of transparencies. For example, the iodine photodissociation lasers (PDL). Some parameters of these lasers are comparable with those of neodimium-doped YAG- or Co2-lasers. Under real conditions of the laser operation when the mixing rate of sublevels of low working state exceeds significantly the relaxation rate of upper state sub levels, the spectrum of iodine laser consists of one component corresponding to the strongest transition 3 yields 4 ((nu) equals 7603.14 cm-1). Such one-frequency spectrum is characteristic of PDL with solar, chemical or xenon lamp radiation pumping (only in the case of compensated magntic field).
This paper describes developed computer code AIRA used to calculate the atmospheric transmittance with a low and medium spectral resolution in the visible and IR. Three basic factors affecting the radiation attenuation (molecular absorption, aerosol extinction, molecular scattering) are included. AIRA calculates molecular absorption, using a band model whose parameters are derived from molecular absorption parameters database. AIRA is used both as a traditional band model and a single-line model. The latter was formerly regarded only as a theoretical treatment. However, it provides a satisfactory agreement with experiments for some H2O and CO2 bands.
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