# Changeset 12046

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Timestamp:
2019-12-04T11:51:54+01:00 (8 months ago)
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Writing the doc for SBCBLK!

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 r12031 \begin{itemize} \item a bulk formulation (\np[=.true.]{ln_blk}{ln\_blk} with four possible bulk algorithms), \item a bulk formulation (\np[=.true.]{ln_blk}{ln\_blk}), featuring a selection of four bulk parameterization algorithms, \item a flux formulation (\np[=.true.]{ln_flx}{ln\_flx}), \item a coupled or mixed forced/coupled formulation (exchanges with a atmospheric model via the OASIS coupler), \label{sec:SBC_blk} % L. Brodeau, December 2019... \begin{listing} \nlst{namsbc_blk} \end{listing} In the bulk formulation, the surface boundary condition fields are computed with bulk formulae using prescribed atmospheric fields and prognostic ocean (and sea-ice) surface variables averaged over \np{nn_fsbc}{nn\_fsbc} time-step. If the bulk formulation is selected (\np[=.true.]{ln_blk}{ln\_blk}), the air-sea fluxes associated with surface boundary conditions are estimated by means of the traditional \emph{bulk formulae}. As input, bulk formulae rely on a prescribed near-surface atmosphere state (typically extracted from a weather reanalysis) and the prognostic sea (-ice) surface state averaged over \np{nn_fsbc}{nn\_fsbc} time-step(s). % Turbulent air-sea fluxes are computed using the sea surface properties and \subsection{Bulk formulae} % In NEMO, when the bulk formulation is selected, surface fluxes are computed by means of the traditional bulk formulae: In NEMO, the set of equations that relate each component of the surface fluxes to the near-surface atmosphere and sea surface states writes % \begin{subequations}\label{eq_bulk} \end{eqnarray} \end{subequations} %lulu % From which, the the non-solar heat flux is $Q_{ns} = Q_L + Q_H + Q_{ir}$ % % with $\theta_z \simeq T_z+\gamma z$ $q_s \simeq 0.98\,q_{sat}(T_s,p_a )$ % from which, the the non-solar heat flux is $Q_{ns} = Q_L + Q_H + Q_{ir}$ % where $\mathbf{\tau}$ is the wind stress vector, $Q_H$ the sensible heat flux, $E$ the evaporation, $Q_L$ the latent heat flux, and $Q_{ir}$ the net longwave and longwave radiative fluxes, respectively. % Note: a positive sign of $\mathbf{\tau}$, $Q_H$, and $Q_L$ means a gain of the relevant quantity for the ocean, while a positive $E$ implies a freshwater loss for the ocean. % $\rho$ is the density of air. $C_D$, $C_H$ and $C_E$ are the BTCs for momentum, sensible heat, and moisture, respectively.  $C_P$ is the heat capacity of moist air, and $L_v$ is the latent heat of vaporization of water.  $\theta_z$, $T_z$ and $q_z$ are the potential temperature, temperature, and specific humidity of air at height $z$, respectively. $\gamma z$ is a temperature correction term which accounts for the adiabatic lapse rate and approximates the potential temperature at height $z$ \citep{Josey_al_2013}.  $\mathbf{U}_z$ is the wind speed vector at height $z$ (possibly referenced to the surface current $\mathbf{u_0}$, section \ref{s_res1}.\ref{ss_current}). The bulk scalar wind speed, $U_B$, is the scalar wind speed, $|\mathbf{U}_z|$, with the potential inclusion of a gustiness contribution (section \ref{s_res2}.\ref{ss_calm}). $P_0$ is the mean sea-level pressure (SLP). Note: a positive sign of $\mathbf{\tau}$, the various fluxes of heat implies a gain of the relevant quantity for the ocean, while a positive $E$ implies a freshwater loss for the ocean. % $\rho$ is the density of air. $C_D$, $C_H$ and $C_E$ are the bulk transfer coefficients for momentum, sensible heat, and moisture, respectively (hereafter referd to as BTCs). % $C_P$ is the heat capacity of moist air, and $L_v$ is the latent heat of vaporization of water. % $\theta_z$, $T_z$ and $q_z$ are the potential temperature, absolute temperature, and specific humidity of air at height $z$ above the sea surface, respectively. $\gamma z$ is a temperature correction term which accounts for the adiabatic lapse rate and approximates the potential temperature at height $z$ \citep{Josey_al_2013}. % $\mathbf{U}_z$ is the wind speed vector at height $z$ above the sea surface (possibly referenced to the surface current $\mathbf{u_0}$, section \ref{s_res1}.\ref{ss_current}). % The bulk scalar wind speed, namely $U_B$, is the scalar wind speed, $|\mathbf{U}_z|$, with the potential inclusion of a gustiness contribution (section \ref{s_res2}.\ref{ss_calm}). % $a$ and $\delta$ are the albedo and emissivity of the sea surface, respectively.\\ % %$p_a$ is the mean sea-level pressure (SLP). % $T_s$ is the sea surface temperature. $q_s$ is the saturation specific humidity of air at temperature $T_s$ and includes a 2\% reduction to account for the presence of salt in seawater \citep{Sverdrup_al_1942,Kraus_Businger_1996}. Depending on the bulk parameterization used, $T_s$ can be the temperature at the air-sea interface (skin temperature, hereafter SSST) or at a few tens of centimeters below the surface (bulk sea surface temperature, hereafter SST). Depending on the bulk parameterization used, $T_s$ can either be the temperature at the air-sea interface (skin temperature, hereafter SSST) or at typically a few tens of centimeters below the surface (bulk sea surface temperature, hereafter SST). % The SSST differs from the SST due to the contributions of two effects of opposite sign, the \emph{cool skin} and \emph{warm layer} (hereafter CSWL). The \emph{cool skin} refers to the cooling of the millimeter-scale uppermost layer of the ocean, in which the net upward flux of heat to the atmosphere is ineffectively sustained by molecular diffusion. As such, a steep vertical gradient of temperature must exist to ensure the heat flux continuity with underlying layers in which the same flux is sustained by turbulence. The \emph{warm layer} refers to the warming of the upper few meters of the ocean under sunny conditions. The CSWL effects are most significant under weak wind conditions due to the absence of substancial surface vertical mixing (caused by \eg breaking waves). The impact of the CSWL on the computed TASFs is discussed in section \ref{s_res1}.\ref{ss_skin}. %%%% Second set of equations (rad): where $a$ and $\delta$ are the albedo and emissivity of the sea surface, respectively. Thus, we use the computed $Q_L$ and $Q_H$ and the 3-hourly surface downwelling shortwave and longwave radiative fluxes ($Q_{sw\downarrow}$ and $Q_{lw\downarrow}$, respectively) from ERA-Interim to correct the daily SST every 3 hours. Due to the implicitness of the problem implied by the dependence of $Q_{nsol}$ on $T_s$, this correction is done iteratively during the computation of the TASFs. opposite sign, the \emph{cool skin} and \emph{warm layer} (hereafter CS and WL, respectively). % Technically, when the ECMWF or COARE* bulk parameterizations are selected (\np[=.true.]{ln_ECMWF}{ln\_ECMWF} or \np[=.true.]{ln_COARE*}{ln\_COARE\*}), $T_s$ is the SSST, as opposed to the NCAR bulk parameterization (\np[=.true.]{ln_NCAR}{ln\_NCAR}) for which $T_s$ is the bulk SST (\ie~temperature at first T-point level). For more details on all these aspects the reader is invited to refer to \citet{brodeau.barnier.ea_JPO17}. \subsubsection{Appropriate use of the  NCAR algorithm} NCAR bulk parameterizations (formerly know as CORE) is meant to be used with the CORE II atmospheric forcing (XXX). Hence the following namelist parameters must be set as follow: NCAR bulk parameterizations (formerly know as CORE) is meant to be used with the CORE II atmospheric forcing \citep{large.yeager_CD09}. Hence the following namelist parameters must be set: % \begin{verbatim} thanks to the \href{https://brodeau.github.io/aerobulk/}{Aerobulk} package (\citet{brodeau.barnier.ea_JPO16}): (\citet{brodeau.barnier.ea_JPO17}): The choice is made by setting to true one of the following namelist