scholarly journals Technical Note: A new discrete ordinate first-order rotational Raman scattering radiative transfer model – implementation and first results

2011 ◽  
Vol 11 (20) ◽  
pp. 10471-10485 ◽  
Author(s):  
A. Kylling ◽  
B. Mayer ◽  
M. Blumthaler
Keyword(s):  
Radiative Transfer ◽  
Raman Scattering ◽  
Solar Spectrum ◽  
Technical Note ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Discrete Ordinate ◽  
First Order ◽  
Spectral Interpolation ◽  
First Results

Abstract. Rotational Raman scattering in the Earth's atmosphere explains the filling-in of Fraunhofer lines in the solar spectrum. A new model including first-order rotational Raman scattering has been developed, based on a reimplementation of the versatile discrete ordinate radiative transfer (DISORT) solver in the C computer language. The solver is fully integrated in the freely available libRadtran radiative transfer package. A detailed description is given of the model including the spectral resolution and a spectral interpolation scheme that considerably speeds up the calculations. The model is used to demonstrate the effect of clouds on top and bottom of the atmosphere filling-in factors and differential optical depths. Cloud effects on vertical profiles of the filling-in factor are also presented. The spectral behaviour of the model is compared against measurements under thunderstorm and aerosol loaded conditions.

scholarly journals Technical Note: A novel parameterization of the transmissivity due to ozone absorption in the <i>k</i>-distribution method and correlated-<i>k</i> approximation of Kato et al. (1999) over the UV band

2015 ◽  
Vol 15 (13) ◽  
pp. 7449-7456 ◽  
Author(s):  
W. Wandji Nyamsi ◽  
A. Arola ◽  
P. Blanc ◽  
A. V. Lindfors ◽  
V. Cesnulyte ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Solar Spectrum ◽  
Ground Level ◽  
Technical Note ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Spectral Interval ◽  
Computationally Efficient ◽  
Ozone Absorption ◽  
Distribution Method

Abstract. The k-distribution method and the correlated-k approximation of Kato et al. (1999) is a computationally efficient approach originally designed for calculations of the broadband solar radiation at ground level by dividing the solar spectrum in 32 specific spectral bands from 240 to 4606 nm. Compared to a spectrally resolved computation, its performance in the UV band appears to be inaccurate, especially in the spectral intervals #3 [283, 307] nm and #4 [307, 328] nm because of inaccuracy in modeling the transmissivity due to ozone absorption. Numerical simulations presented in this paper indicate that a single effective ozone cross section is insufficient to accurately represent the transmissivity over each spectral interval. A novel parameterization of the transmissivity using more quadrature points yields maximum errors of respectively 0.0006 and 0.0143 for intervals #3 and #4. How to practically implement this new parameterization in a radiative transfer model is discussed for the case of libRadtran (library for radiative transfer). The new parameterization considerably improves the accuracy of the retrieval of irradiances in UV bands.

scholarly journals Improvement of the Simulation of Cloud Longwave Scattering in Broadband Radiative Transfer Models

2018 ◽  
Vol 75 (7) ◽  
pp. 2217-2233 ◽  
Author(s):  
Guanglin Tang ◽  
Ping Yang ◽  
George W. Kattawar ◽  
Xianglei Huang ◽  
Eli J. Mlawer ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Multiple Scattering ◽  
General Circulation ◽  
General Circulation Models ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Discrete Ordinate ◽  
Wide Range ◽  
Scaling Methods ◽  
Computational Errors

Abstract Cloud longwave scattering is generally neglected in general circulation models (GCMs), but it plays a significant and highly uncertain role in the atmospheric energy budget as demonstrated in recent studies. To reduce the errors caused by neglecting cloud longwave scattering, two new radiance adjustment methods are developed that retain the computational efficiency of broadband radiative transfer simulations. In particular, two existing scaling methods and the two new adjustment methods are implemented in the Rapid Radiative Transfer Model (RRTM). The results are then compared with those based on the Discrete Ordinate Radiative Transfer model (DISORT) that explicitly accounts for multiple scattering by clouds. The two scaling methods are shown to improve the accuracy of radiative transfer simulations for optically thin clouds but not effectively for optically thick clouds. However, the adjustment methods reduce computational errors over a wide range, from optically thin to thick clouds. With the adjustment methods, the errors resulting from neglecting cloud longwave scattering are reduced to less than 2 W m−2 for the upward irradiance at the top of the atmosphere and less than 0.5 W m−2 for the surface downward irradiance. The adjustment schemes prove to be more accurate and efficient than a four-stream approximation that explicitly accounts for multiple scattering. The neglect of cloud longwave scattering results in an underestimate of the surface downward irradiance (cooling effect), but the errors are almost eliminated by the adjustment methods (warming effect).

SHDOMPPDA: A Radiative Transfer Model for Cloudy Sky Data Assimilation

2007 ◽  
Vol 64 (11) ◽  
pp. 3854-3864 ◽  
Author(s):  
K. Franklin Evans
Keyword(s):  
Radiative Transfer ◽  
Data Assimilation ◽  
Spherical Harmonics ◽  
Forward Model ◽  
Radiative Transfer Model ◽  
Computational Time ◽  
Transfer Model ◽  
Discrete Ordinate Method ◽  
Discrete Ordinate ◽  
Plane Parallel

Abstract The spherical harmonics discrete ordinate method for plane-parallel data assimilation (SHDOMPPDA) model is an unpolarized plane-parallel radiative transfer forward model, with corresponding tangent linear and adjoint models, suitable for use in assimilating cloudy sky visible and infrared radiances. It is derived from the spherical harmonics discrete ordinate method plane-parallel (SHDOMPP, also described in this article) version of the spherical harmonics discrete ordinate method (SHDOM) model for three-dimensional atmospheric radiative transfer. The inputs to the SHDOMPPDA forward model are profiles of pressure, temperature, water vapor, and mass mixing ratio and number concentration for a number of hydrometeor species. Hydrometeor optical properties, including detailed phase functions, are determined from lookup tables as a function of mass mean radius. The SHDOMPP and SHDOMPPDA algorithms and construction of the tangent-linear and adjoint models are described. The SHDOMPPDA forward model is validated against the Discrete Ordinate Radiative Transfer Model (DISORT) by comparing upwelling radiances in multiple directions from 100 cloud model columns at visible and midinfrared wavelengths. For this test in optically thick clouds the computational time for SHDOMPPDA is comparable to DISORT for visible reflection, and roughly 5 times faster for thermal emission. The tangent linear and adjoint models are validated by comparison to finite differencing of the forward model.

A First-Order Radiative Transfer Model for Microwave Radiometry of Forest Canopies at L-Band

2011 ◽  
Vol 49 (9) ◽  
pp. 3167-3179 ◽  
Author(s):  
Mehmet Kurum ◽  
Roger H. Lang ◽  
Peggy E. O'Neill ◽  
Alicia T. Joseph ◽  
Thomas J. Jackson ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Microwave Radiometry ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Forest Canopies ◽  
First Order ◽  
L Band

scholarly journals Technical Note: A novel parameterization of the transmissivity due to ozone absorption in the <i>k</i>-distribution method and correlated-<i>k</i> approximation of Kato et al. (1999) over the UV band

2015 ◽  
Vol 15 (1) ◽  
pp. 1027-1040
Author(s):  
W. Wandji Nyamsi ◽  
A. Arola ◽  
P. Blanc ◽  
A. V. Lindfors ◽  
V. Cesnulyte ◽  
...  
Keyword(s):  
Solar Spectrum ◽  
Ground Level ◽  
Maximum Error ◽  
Technical Note ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Spectral Interval ◽  
Computationally Efficient ◽  
Ozone Absorption ◽  
Distribution Method

Abstract. The k-distribution method and the correlated-k approximation of Kato et al. (1999) is a computationally efficient approach originally designed for calculations of the broadband solar radiation at ground level by dividing the solar spectrum in 32 specific spectral bands from 240 to 4606 nm. Compared to a spectrally-resolved computation, its performance in the UV band appears to be inaccurate, especially in the spectral intervals #3 [283, 307] nm and #4 [307, 328] nm because of inaccuracy in modelling the transmissivity due to ozone absorption. Numerical simulations presented in this paper indicate that a single effective ozone cross section is insufficient to accurately represent the transmissivity over each spectral interval. A novel parameterization of the transmissivity using more quadrature points yields maximum error of respectively 0.0006 and 0.0041 for interval #3 and #4. How to practically implement this new parameterization in a radiative transfer model is discussed for the case of libRadtran.

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