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branches/nemo_v3_3_beta/DOC/TexFiles/Chapters/Chap_SBC.tex
r2282 r2349 1 ================================================================1 % ================================================================ 2 2 % Chapter Ñ Surface Boundary Condition (SBC) 3 3 % ================================================================ … … 15 15 The ocean needs six fields as surface boundary condition: 16 16 \begin{itemize} 17 \item the two components of the surface ocean stress $\left( {\tau _u \;,\;\tau _v} \right)$18 \item the incoming solar and non solar heat fluxes $\left( {Q_{ns} \;,\;Q_{sr} } \right)$19 \item the surface freshwater budget $\left( {\textit{emp},\;\textit{emp}_S } \right)$17 \item the two components of the surface ocean stress $\left( {\tau _u \;,\;\tau _v} \right)$ 18 \item the incoming solar and non solar heat fluxes $\left( {Q_{ns} \;,\;Q_{sr} } \right)$ 19 \item the surface freshwater budget $\left( {\textit{emp},\;\textit{emp}_S } \right)$ 20 20 \end{itemize} 21 22 Four different ways to provide those six fields to the ocean are available which 23 are controlled by namelist variables: an analytical formulation (\np{ln\_ana}=true), 24 a flux formulation (\np{ln\_flx}=true), a bulk formulae formulation (CORE 25 (\np{ln\_core}=true) or CLIO (\np{ln\_clio}=true) bulk formulae) and a coupled 21 plus an optional field: 22 \begin{itemize} 23 \item the atmospheric pressure at the ocean surface $\left( p_a \right)$ 24 \end{itemize} 25 26 Four different ways to provide the first six fields to the ocean are available which 27 are controlled by namelist variables: an analytical formulation (\np{ln\_ana}~=~true), 28 a flux formulation (\np{ln\_flx}~=~true), a bulk formulae formulation (CORE 29 (\np{ln\_core}~=~true) or CLIO (\np{ln\_clio}~=~true) bulk formulae) and a coupled 26 30 formulation (exchanges with a atmospheric model via the OASIS coupler) 27 (\np{ln\_cpl}=true). The frequency at which the six fields have to be updated is 28 the \np{nf\_sbc} namelist parameter. 31 (\np{ln\_cpl}~=~true). The optional atmospheric pressure can be used either 32 to force ocean and ice dynamics (\np{ln\_apr\_dyn}~=~true), or in the bulk 33 formulae computation (\np{ln\_apr\_dyn}~=~true) 34 \footnote{None of the two current bulk formulea (CLIO and CORE) uses the 35 atmospheric pressure field.}. 36 The frequency at which the six or seven fields have to be updated is the \np{nn\_fsbc} 37 namelist parameter. 29 38 When the fields are supplied from data files (flux and bulk formulations), the input fields 30 39 need not be supplied on the model grid. Instead a file of coordinates and weights can … … 34 43 These options control the rotation of vector components supplied relative to an east-north 35 44 coordinate system onto the local grid directions in the model; the addition of a surface 36 restoring term to observed SST and/or SSS (\np{ln\_ssr} =true); the modification of fluxes45 restoring term to observed SST and/or SSS (\np{ln\_ssr}~=~true); the modification of fluxes 37 46 below ice-covered areas (using observed ice-cover or a sea-ice model) 38 (\np{nn\_ice} =0,1, 2 or 3); the addition of river runoffs as surface freshwater39 fluxes (\np{ln\_rnf}=true); the addition of a freshwater flux adjustment in40 order to avoid a mean sea-level drift (\np{nn\_fwb}= 0, 1 or2); and the47 (\np{nn\_ice}~=~0,1, 2 or 3); the addition of river runoffs as surface freshwater 48 fluxes or lateral inflow (\np{ln\_rnf}~=~true); the addition of a freshwater flux adjustment 49 in order to avoid a mean sea-level drift (\np{nn\_fwb}~=~0,~1~or~2); and the 41 50 transformation of the solar radiation (if provided as daily mean) into a diurnal 42 cycle (\np{ln\_dm2dc} =true).51 cycle (\np{ln\_dm2dc}~=~true). 43 52 44 53 In this chapter, we first discuss where the surface boundary condition appears in the … … 127 136 %created!) 128 137 % 129 %Especially the \np{n f\_sbc}, the \mdl{sbc\_oce} module (fluxes + mean sst sss ssu138 %Especially the \np{nn\_fsbc}, the \mdl{sbc\_oce} module (fluxes + mean sst sss ssu 130 139 %ssv) i.e. information required by flux computation or sea-ice 131 140 % … … 181 190 %-------------------------------------------------------------------------------------------------------------- 182 191 183 184 192 The analytical formulation of the surface boundary condition is the default scheme. 185 193 In this case, all the six fluxes needed by the ocean are assumed to … … 265 273 the turbulent transfer coefficients (momentum, sensible heat and evaporation) 266 274 from the 10 metre wind speed, air temperature and specific humidity. 275 This \citet{Large_Yeager_Rep04} dataset is available through the GFDL web 276 site (http://nomads.gfdl.noaa.gov/nomads/forms/mom4/CORE.html). 267 277 268 278 Note that substituting ERA40 to NCEP reanalysis fields 269 279 does not require changes in the bulk formulea themself. 280 This is the so-called DRAKKAR Forcing Set (DFS) \citep{Brodeau_al_OM09}. 270 281 271 282 The required 8 input fields are: … … 345 356 346 357 In the coupled formulation of the surface boundary condition, the fluxes are 347 provided by the OASIS coupler at each \np{nf\_cpl} time-step, while sea and ice 348 surface temperature, ocean and ice albedo, and ocean currents are sent to 349 the atmospheric component. 350 351 The generalised coupled interface is under development. It should be available 352 in summer 2008. It will include the ocean interface for most of the European 353 atmospheric GCM (ARPEGE, ECHAM, ECMWF, HadAM, LMDz). 358 provided by the OASIS coupler at a frequency which is defined in the OASIS coupler, 359 while sea and ice surface temperature, ocean and ice albedo, and ocean currents 360 are sent to the atmospheric component. 361 362 A generalised coupled interface has been developed. It is currently interfaced with OASIS 3 363 (\key{oasis3}) and does not support OASIS 4 364 \footnote{The \key{oasis4} exist. It activates portion of the code that are still under development.}. 365 It has been successfully used to interface \NEMO to most of the European atmospheric 366 GCM (ARPEGE, ECHAM, ECMWF, HadAM, LMDz), 367 as well as to WRF (Weather Research and Forecasting Model) (http://wrf-model.org/). 368 369 Note that in addition to the setting of \np{ln\_cpl} to true, the \key{coupled} have to be defined. 370 The CPP key is mainly used in sea-ice to ensure that the atmospheric fluxes are 371 actually recieved by the ice-ocean system (no calculation of ice sublimation in coupled mode). 372 When PISCES biogeochemical model (\key{top} and \key{pisces}) is also used in the coupled system, 373 the whole carbon cycle is computed by defining \key{cpl\_carbon\_cycle}. In this case, 374 CO$_2$ fluxes are exchanged between the atmosphere and the ice-ocean system. 375 376 377 % ================================================================ 378 % Atmospheric pressure 379 % ================================================================ 380 \section [Atmospheric pressure (\textit{sbcapr})] 381 {Atmospheric pressure (\mdl{sbcapr})} 382 \label{SBC_apr} 383 %------------------------------------------namsbc_apr---------------------------------------------------- 384 \namdisplay{namsbc_apr} 385 %------------------------------------------------------------------------------------------------------------- 386 387 The optional atmospheric pressure can be used either to force ocean and ice dynamics 388 (\np{ln\_apr\_dyn}~=~true), or in the bulk formulae computation (\np{ln\_apr\_dyn}~=~true). 389 The input atmospheric forcing is interpolated in time to the model time step, and optionally 390 in space when interpolation on-the-fly is used. When used to force the dynamics, it is further 391 transformed into an equivalent inverse barometer sea surface height, $\eta_{ib}$, using: 392 \begin{equation} \label{SBC_ssh_ib} 393 \eta_{ib} = - \frac{1}{g\,\rho_o} \left( P_{atm} - P_o \right) 394 \end{equation} 395 where $P_{atm}$ is the atmospheric pressure and $P_o$ a reference atmospheric pressure. 396 A value of $101,000~N/m^2$ is used unless \np{ln\_ref\_apr} is set to true. In this case $P_o$ 397 is set to the value of $P_{atm}$ averaged over the ocean domain, $i.e.$ the mean value of 398 $\eta_{ib}$ is kept to zero at all time step. 399 400 A gradient of $\eta_{ib}$ is added to the RHS of the ocean momentum equation 401 (see \mdl{dynspg} for the ocean). For sea-ice, the sea surface height, $\eta_m$, 402 which is provided to the sea ice model is set to $\eta - \eta_{ib}$ (see \mdl{sbcssr} module). 403 Furthermore, $\eta_{ib}$ can be set in the output. This simplifies the altirmetry data 404 and model comparison as inverse barometer sea surface height is usually removed 405 from thise date prior to their distribution. 354 406 355 407 % ================================================================ 356 408 % River runoffs 357 409 % ================================================================ 358 \section [ river runoffs (\textit{sbcrnf})]359 { river runoffs (\mdl{sbcrnf})}410 \section [River runoffs (\textit{sbcrnf})] 411 {River runoffs (\mdl{sbcrnf})} 360 412 \label{SBC_rnf} 361 413 %------------------------------------------namsbc_rnf---------------------------------------------------- … … 392 444 required to properly represent the diurnal cycle \citep{Bernie_al_JC05}. see also \S\ref{SBC_dcy}.}. 393 445 394 As such from V N3.3 onwards it is possible to add river runoff through a non-zero depth, and for the446 As such from V~3.3 onwards it is possible to add river runoff through a non-zero depth, and for the 395 447 temperature and salinity of the river to effect the surrounding ocean. 396 448 The user is able to specify, in a NetCDF input file, the temperature and salinity of the river, along with the … … 411 463 After the user specified depth is read ini, the number of grid boxes this corresponds to is 412 464 calculated and stored in the variable \np{nz\_rnf}. 413 The variable \ np{h\_dep} is then calculated to be the depth (in metres) of the bottom of the465 The variable \textit{h\_dep} is then calculated to be the depth (in metres) of the bottom of the 414 466 lowest box the river water is being added to (i.e. the total depth that river water is being added to in the model). 415 467 416 The mass/volume addition due to the river runoff is, at each relevant depth level, added to the horizontal divergence (\np{hdivn})417 in the subroutine \np{sbc\_rnf\_div} (called from \np{divcur}).468 The mass/volume addition due to the river runoff is, at each relevant depth level, added to the horizontal divergence 469 (\textit{hdivn}) in the subroutine \rou{sbc\_rnf\_div} (called from \mdl{divcur}). 418 470 This increases the diffusion term in the vicinity of the river, thereby simulating a momentum flux. 419 471 The sea surface height is calculated using the sum of the horizontal divergence terms, and so the 420 472 river runoff indirectly forces an increase in sea surface height. 421 473 422 The \ np{hdivn} terms are used in the tracer advection modules to force vertical velocities.474 The \textit{hdivn} terms are used in the tracer advection modules to force vertical velocities. 423 475 This causes a mass of water, equal to the amount of runoff, to be moved into the box above. 424 476 The heat and salt content of the river runoff is not included in this step, and so the tracer … … 430 482 As such the volume of water does not change, but the water is diluted. 431 483 432 For the non-linear free surface case ( vvl), no flux is allowed through the surface.484 For the non-linear free surface case (\key{vvl}), no flux is allowed through the surface. 433 485 Instead in the surface box (as well as water moving up from the boxes below) a volume of runoff water 434 486 is added with no corresponding heat and salt addition and so as happens in the lower boxes there is a dilution effect. … … 499 551 the diurnal cycle of SWF is a scaling of the top of the atmosphere diurnal cycle 500 552 of incident SWF. The \cite{Bernie_al_CD07} reconstruction algorithm is available 501 in \NEMO by setting \np{ln\_dm2dc} =true (a \textit{namsbc} namelist parameter) when using502 CORE bulk formulea (\np{ln\_blk\_core} =true) or the flux formulation (\np{ln\_flx}=true).553 in \NEMO by setting \np{ln\_dm2dc}~=~true (a \textit{namsbc} namelist parameter) when using 554 CORE bulk formulea (\np{ln\_blk\_core}~=~true) or the flux formulation (\np{ln\_flx}~=~true). 503 555 The reconstruction is performed in the \mdl{sbcdcy} module. The detail of the algoritm used 504 556 can be found in the appendix~A of \cite{Bernie_al_CD07}. The algorithm preserve the daily … … 663 715 %------------------------------------------------------------------------------------------------------------- 664 716 665 In forced mode using a flux formulation ( default option or \key{flx} defined), a717 In forced mode using a flux formulation (\np{ln\_flx}~=~true), a 666 718 feedback term \emph{must} be added to the surface heat flux $Q_{ns}^o$: 667 719 \begin{equation} \label{Eq_sbc_dmp_q}
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