htgop_doc

gas_opt_prop_en.tex (10354B)

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 \begin{document}
 
 
 \title{High-Tune: gas optical properties file format}
 
 \maketitle
 \begin{center}
 \author{\bf|Méso|Star>}\\
  (\url{https://www.meso-star.com}) \\
 \end{center}
 \vspace{1cm}
 
 \tableofcontents
 
 \newpage
 \section{Context}
 This document describes the format of the file that provides all required optical properties (absorption and scattering coefficients, both in the LW and SW regions) of the {\bf gas mixture} only.
 This data file uses the ASCII format, and the following convention: each data array is first described by a comment, then the numeric data is provided. A single numeric value is given for each line. A array of size $N$ is therefore provided over $N$ lines.
 
 \section{Description of the model and data usage}
 
 Data is provided for a stratified plane-parallel atmosphere: the atmosphere is described using $N_{lev}$ (pressure, or altitude) levels that define $N_{lay}=N_{lev}-1$ layers. Some data is defined at each level, some is defined for layers (using the hypothesis of homogeneous layers). Finally, two spectral domains are described: the longwave (LW) and the shortwave (SW) domains. For each one of these domains, a number of spectral intervals are defined, and a number of quadrature points is given in each interval (variable).
 
 \begin{figure}[!h]
 \centering
 \includegraphics[width=0.80\textwidth,angle=0]{./figures/ka_lw.pdf}
 \caption[]{Evolution of the absorption coefficient for the 10 quadrature points of the first LW spectral interval, for the first atmospheric layer (MLS profile) as a function of water vapor molar fraction.}
 \label{fig:ka_lw}
 \end{figure}
 
 Optical properties of the gas mixture (absorption and scattering coefficients) can be computed from the data provided in this file, and from the local water vapor content (provided in the LES data file). The atmospheric data file contains the values of the absorption and scattering coefficients of the gas mixture, tabulated as a function of the water vapor molar fraction $x_{H_{2}O}$. Figure \ref{fig:ka_lw} shows that the logarithm of the absorption coefficient evolves linearly with the logarithm of $x_{H_{2}O}$ over a wide range of water vapor molar fraction, for each quadrature point. Interpolating the optical properties of the gas mixture for any given value of $x_{H_{2}O}(local)$ is therefore very simple using the data of the atmospheric file.
 
 \begin{figure}[htbp]
 %  \hspace*{-2.2cm}
   \centering
   \mbox{
     \subfigure[]{
       \includegraphics[width=0.50\textwidth]{./figures/si_flux_nominal_lw.pdf}
     }
     \quad
     \hspace{-0.5cm}
     \subfigure[]{
       \includegraphics[width=0.50\textwidth]{./figures/dsi_flux_lw.pdf}
     }
   }
   \caption{(a) Spectrally integrated LW flux profile obtained using the nominal absorption optical depth of ECRAD over a standard MLS profile; (b) Difference over spectrally integrated LW fluxes computed using nominal absorption optical thicknesses and the absorption optical thicknesses that have been obtained from tabulated data and nominal values of $x_{H_{2}O}$}.
   \label{fig:si_flux_lw}
 \end{figure}
 
 \begin{figure}[htbp]
 %  \hspace*{-2.2cm}
   \centering
   \mbox{
     \subfigure[]{
       \includegraphics[width=0.50\textwidth]{./figures/si_flux_nominal_sw.pdf}
     }
     \quad
     \hspace{-0.5cm}
     \subfigure[]{
       \includegraphics[width=0.50\textwidth]{./figures/dsi_flux_sw.pdf}
     }
   }
   \caption{(a) Spectrally integrated SW flux profile obtained using the nominal absorption optical depth of ECRAD over a standard MLS profile; (b) Difference over spectrally integrated SW fluxes computed using nominal absorption optical thicknesses and the absorption optical thicknesses that have been obtained from tabulated data and nominal values of $x_{H_{2}O}$}
   \label{fig:si_flux_sw}
 \end{figure}
 
 The linearity of optical properties with water vapor molar fraction has been validated on the following basis: a radiative transfer code (LW and SW) based on anaytic radiative transfer solutions obtained in a clear-sky situation (without scattering) has been adapted in order to use k-distribution spectral data with a variable quadrature order (such as ECRAD spectral data). Two LW radiative transfer computations have been performed with a modified MLS atmospheric profile: the column containing the highest specific humidity has been identified. The vertical profile of $x_{H_{2}O}$ in the original MLS profile has then been replaced with the data of this specific atmospheric column for all columns of the LES zone (for z < 4 km) and has not the modified out of this zone. The two radiative transfer computations have then used:
 \begin{itemize}
 \item absorption coefficients obtained from ECRAD for the modified MLS atmospheric profile. Results are presented in figure \ref{fig:si_flux_lw}(a) for the LW and figure \ref{fig:si_flux_sw}(a) for the SW.
 \item absorption coefficients that have been interpolated from the local values of $x_{H_{2}O}$ using the tabulation of optical properties established on the basis of 20 values of $x_{H_{2}O}$ uniformly spaced (on a logarithmic scale) between 10$^{-6}$ and 1. Figure \ref{fig:si_flux_lw}(b) displays differences between LW radiative flux obtained using this method and previous (reference) results. Figure \ref{fig:si_flux_sw}(b) displays the same differences in the SW domain.
 \end{itemize}
 
 Results being extremely close, the possibility to obtain optical properties of the gas mixture from the tabulated values and the local value of $x_{H_{2}O}$ is considered as validated.
 
 \newpage
 \section{File format}
 
 The atmospheric file contains the following data, separated by comments:
 
 \begin{itemize}
 \item The number of atmospheric levels $N_{lev}$ (1 integer)
 \item The number of atmospheric layers $N_{lay}$ (1 integer)
 \item Ground temperature (1 real) [K]
 \item Pressure at each level ($N_{lev}$ reals) [Pa]
 \item Temperature at each level ($N_{lev}$ reals) [K]
 \item Altitude at each level ($N_{lev}$ reals) [m]
 \item The nominal water vapor molar fration in the mixture $x_{H_{2}O}(nominal)$, for each layer ($N_{lay}$ reals) [mol of $H_{2}O$ per mol of mixture]
 \item The number of water vapor molar fraction vertical profiles $x_{H_{2}O}$ for the tabulation ($N_{w}$).
 \item For each one of the $N_{w}$ vertical profiles of $x_{H_{2}O}$ in the table: the value of $x_{H_{2}O}$ for each one of the $N_{lay}$ atmospheric layers. ($N_{w}$x$N_{lay} reals$) [mol of $H_{2}O$ per mol of mixture]
 \item The emissivity of the ground in the LW domain (1 real)
 \item The emissivity of the ground for the SW domain (1 real)
 \item The number of spectral intervals $N_{b,LW}$ for the LW domain (1 integer)
 \item The number of spectral intervals $N_{b,SW}$ for the SW domain (1 integer)
 \item For each $i_{b} \in [1,N_{b,LW}]$ LW interval:
 \begin{itemize}
 \item the lower wavenumber of the interval (1 real) [cm$^{-1}$]
 \item the higher wavenumber of the interval (1 real) [cm$^{-1}$]
 \item the number of quadrature points $N_{g}(i_{b})$ (1 integer)
 \item the $N_{g}(i_{b})$ values of the quadrature weight for the interval ($N_{g}(i_{b})$ reals)
 \end{itemize}
 \item For each $i_{b} \in [1,N_{b,SW}]$ SW interval:
 \begin{itemize}
 \item the lower wavenumber of the interval (1 real) [cm$^{-1}$]
 \item the higher wavenumber of the interval (1 real) [cm$^{-1}$]
 \item the number of quadrature points $N_{g}(i_{b})$ (1 integer)
 \item the $N_{g}(i_{b})$ values of the quadrature weight for the interval ($N_{g}(i_{b})$ reals)
 \end{itemize}
 \item For each $i_{b} \in [1,N_{b,LW}]$ LW interval, and for each $i_{g} \in [1,N_{g}(i_{b})]$ quadrature points:
 \begin{itemize}
 \item the {\bf nominal} absorption coefficient of the gas mixture, for each layer ($N_{lay}$ reals) [m$^{-1}$]
 \item the absorption coefficient of the gas mixture {\bf for each tabulation point} $i_{w}$, for each layer ($N_{w}$x$N_{lay}$ reals) [m$^{-1}$]
 \end{itemize}
 \item For each $i_{b} \in [1,N_{b,SW}]$ SW interval, and for each $i_{g} \in [1,N_{g}(i_{b})]$ quadrature point:
 \begin{itemize}
 \item the {\bf nominal} absorption coefficient of the gas mixture, for each layer ($N_{lay}$ reals) [m$^{-1}$]
 \item the absorption coefficient of the gas mixture {\bf for each tabulation point} $i_{w}$, for each layer ($N_{w}$x$N_{lay}$ reals) [m$^{-1}$]
 \end{itemize}
 \item For each $i_{b} \in [1,N_{b,SW}]$ SW interval, and for each $i_{g} \in [1,N_{g}(i_{b})]$ quadrature point:
 \begin{itemize}
 \item the {\bf nominal} scattering coefficient of the gas mixture, for each layer ($N_{lay}$ reals) [m$^{-1}$]
 \item the scattering coefficient of the gas mixture {\bf for each tabulation point} $i_{w}$, for each layer ($N_{w}$x$N_{lay}$ reals) [m$^{-1}$]
 \end{itemize}
 
 \end{itemize}
 
 A example of (fortran) routine used to read this file is provided below (``input.for'' file):
 
 \lstinputlisting[language=fortran]{./source_files/input.for}
 
 \end{document}