Changeset 994 for trunk/DOC/TexFiles/Chapters/Chap_SBC.tex
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r817 r994 6 6 \minitoc 7 7 8 \ begin{verbatim}9 At the time of this writing, the new surface module 10 that is described in this chapter (SBC) is not yet part 11 of the current distribution. The current way to specify 12 the surface boundary condition is such a mess that we 13 did not attempt to describe it. Nevertheless, apart from 14 the way the surface forcing is implemented, the infor- 15 mation given here are relevant for a NEMO v2.3 user. 16 \ end{verbatim}17 18 The ocean needs 7 fields as surface boundary condition: 19 20 The two components of the surface ocean stress $\left( {\tau _u \;,\;\tau _v} \right)$ 21 22 The incoming solar and non solar heat fluxes $\left( {Q_{ns} \;,\;Q_{sr} } \right)$ 23 24 The surface freshwater budget $\left( {\text{EMP}\;,\;\text{EMP}_S } \right)$ 25 26 \colorbox {yellow}{ The river runoffs (RUNOFF)} 27 28 Four different ways are offered to provide those 7 fields to the ocean: an29 analytical formulation, a flux formulation, a bulk formulae formulation30 (CORE or CLIO bulk formulae) and a coupled formulation (exchanges with a31 atmospheric model via OASIS coupler). In addition, the resulting fields can32 be further modified on used demand via several namelist options. These options33 control the addition of a surface restoring term to observed SST and/or SSS,34 the modification of fluxes below ice-covered area (using observed ice-cover35 or a sea-ice model), the addition of river runoffs as surface freshwater36 fluxes, and the addition of a freshwater flux adjustment on order to avoid a37 mean sea-level drift.8 \newpage 9 $\ $\newline % force a new ligne 10 %---------------------------------------namsbc-------------------------------------------------- 11 \namdisplay{namsbc} 12 %-------------------------------------------------------------------------------------------------------------- 13 $\ $\newline % force a new ligne 14 15 The ocean needs six fields as surface boundary condition: 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 $\left( {\text{EMP},\;\text{EMP}_S } \right)$ 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 26 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. 29 In addition, the resulting fields can be further modified using 30 several namelist options. These options control the addition of a surface restoring 31 term to observed SST and/or SSS (\np{ln\_ssr}=true), the modification of fluxes 32 below ice-covered areas (using observed ice-cover or a sea-ice model) 33 (\np{nn\_ice}=0,1, 2 or 3), the addition of river runoffs as surface freshwater 34 fluxes (\np{ln\_rnf}=true), the addition of a freshwater flux adjustment in 35 order to avoid a mean sea-level drift (\np{nn\_fwb}= 0, 1 or 2), and the 36 transformation of the solar radiation (if provided as daily mean) into a diurnal 37 cycle (\np{ln\_dm2dc}=true). 38 38 39 39 In this chapter, we first discuss where the surface boundary condition 40 40 appears in the model equations. Then we present the four ways of providing 41 the surface boundary condition. Finally, the different options that modify 42 the fluxes inside the ocean are discussed. 43 44 45 46 47 48 49 50 51 41 the surface boundary condition. Finally, the different options that further modify 42 the fluxes applied to the ocean are discussed. 52 43 53 44 … … 60 51 61 52 The surface ocean stress is the stress exerted by the wind and the sea-ice 62 on the ocean. Their two components are assumed to be interpolated on the 63 ocean mesh, i.e. provided at U- and V-points and projected onto the 64 (\textbf{i},\textbf{j}) referential. They are applied as a surface boundary 65 condition of the computation of the momentum vertical mixing trend 66 (\textbf{dynzdf} module) : 53 on the ocean. The two components of stress are assumed to be interpolated 54 onto the ocean mesh, $i.e.$ resolved onto the model (\textbf{i},\textbf{j}) direction 55 at $u$- and $v$-points They are applied as a surface boundary condition of the 56 computation of the momentum vertical mixing trend (\mdl{dynzdf} module) : 67 57 \begin{equation} \label{Eq_sbc_dynzdf} 68 58 \left.{\left( {\frac{A^{vm} }{e_3 }\ \frac{\partial \textbf{U}_h}{\partial k}} \right)} \right|_{z=1} … … 72 62 stress vector in the $(\textbf{i},\textbf{j})$ coordinate system. 73 63 74 The surface heat flux is decomposed in two parts, a non solar andsolar heat75 flux es. The former is the non penetrative part of the heat flux (i.e.76 sensible plus latent plus long wave heat fluxes). It is applied as a surface77 boundary condition trend of the first level temperature time evolution78 equation (\mdl{trasbc} module).64 The surface heat flux is decomposed into two parts, a non solar and a solar heat 65 flux, $Q_{ns}$ and $Q_{sr}$, respectively. The former is the non penetrative part 66 of the heat flux ($i.e.$ the sum of sensible, latent and long wave heat fluxes). 67 It is applied as a surface boundary condition trend of the first level temperature 68 time evolution equation (\mdl{trasbc} module). 79 69 \begin{equation} \label{Eq_sbc_trasbc_q} 80 70 \frac{\partial T}{\partial t}\equiv \cdots \;+\;\left. {\frac{Q_{ns} }{\rho 81 71 _o \;C_p \;e_{3T} }} \right|_{k=1} \quad 82 72 \end{equation} 83 84 The latter is the penetrative part of the heat flux. It is applied as a 3D 85 trends of the temperature equation (\mdl{traqsr} module) when \np{ln\_traqsr}=T. 73 $Q_{sr}$ is the penetrative part of the heat flux. It is applied as a 3D 74 trends of the temperature equation (\mdl{traqsr} module) when \np{ln\_traqsr}=True. 86 75 87 76 \begin{equation} \label{Eq_sbc_traqsr} … … 89 78 \,e_{3T} }\delta _k \left[ {I_w } \right] 90 79 \end{equation} 91 92 where $I_w$ is an adimensional function that describes the way the light 80 where $I_w$ is a non-dimensional function that describes the way the light 93 81 penetrates inside the water column. It is generally a sum of decreasing 94 exponential (see \S\ref{TRA_qsr}).95 96 The surface freshwater budget is provided through two non-necessary97 identical fields EMP and EMP$_S $. Indeed, a surface freshwater98 flux has two effects: it changes the volume of the ocean and it changes the99 s urface concentration of salt (an others tracers). Therefore it appears in100 the sea surface height and salinity time evolution equations as a volume101 flux, EMP (\textit{dynspg\_xxx} modules), andconcentration/dilution effect,102 EMP$_{S}$ (\mdl{trasbc} module) , respectively.82 exponentials (see \S\ref{TRA_qsr}). 83 84 The surface freshwater budget is provided by fields: EMP and EMP$_S$ which 85 may or may not be identical. Indeed, a surface freshwater flux has two effects: 86 it changes the volume of the ocean and it changes the surface concentration of 87 salt (and other tracers). Therefore it appears in the sea surface height as a volume 88 flux, EMP (\textit{dynspg\_xxx} modules), and in the salinity time evolution equations 89 as a concentration/dilution effect, 90 EMP$_{S}$ (\mdl{trasbc} module). 103 91 \begin{equation} \label{Eq_trasbc_emp} 104 92 \begin{aligned} … … 109 97 \end{equation} 110 98 111 In the real ocean, EMP =EMP$_S$ and the ocean salt content is conserved,99 In the real ocean, EMP$=$EMP$_S$ and the ocean salt content is conserved, 112 100 but it exist several numerical reasons why this equality should be broken. 113 101 For example: 114 102 115 103 When rigid-lid assumption is made, the ocean volume becomes constant and 116 thus, EMP =0, not EMP$_{S }$.117 118 When a sea-ice model is considered, the water exchanged between ice and119 ocean is verylightly salty (mean sea-ice salinity is $\sim $\textit{4 psu}). In this case,104 thus, EMP$=$0, not EMP$_{S }$. 105 106 When the ocean is coupled to a sea-ice model, the water exchanged between ice and 107 ocean is slightly salty (mean sea-ice salinity is $\sim $\textit{4 psu}). In this case, 120 108 EMP$_{S}$ take into account both concentration/dilution effect associated with 121 freezing/melting together withsalt flux between ice and ocean, while EMP is109 freezing/melting and the salt flux between ice and ocean, while EMP is 122 110 only the volume flux. In addition, in the current version of \NEMO, the 123 111 sea-ice is assumed to be above the ocean. Freezing/melting does not change 124 the ocean volume (not impact on EMP) while it modifies the SSS125 \colorbox{yellow}{(see {\S} on LIM sea-ice model)}.126 127 Note that SST can also be modified by a freshwater flux. Precipitation s(in128 particular solid one) may have a temperature significantly different from112 the ocean volume (not impact on EMP) but it modifies the SSS. 113 %gm \colorbox{yellow}{(see {\S} on LIM sea-ice model)}. 114 115 Note that SST can also be modified by a freshwater flux. Precipitation (in 116 particular solid precipitation) may have a temperature significantly different from 129 117 the SST. Due to the lack of information about the temperature of 130 precipitation s, we assume it is equal to the SST. Therefore, no118 precipitation, we assume it is equal to the SST. Therefore, no 131 119 concentration/dilution term appears in the temperature equation. It has to 132 be emphasised that this absence does not mean that there is no theat flux133 associated with precipitation! An excess of precipitation will change the134 ocean heat content and is therefore associated with a heat flux (not120 be emphasised that this absence does not mean that there is no heat flux 121 associated with precipitation! Precipitation can change the ocean volume and thus the 122 ocean heat content. It is therefore associated with a heat flux (not yet 135 123 diagnosed in the model) \citep{Roullet2000}). 136 124 137 \colorbox{yellow}{Miss: } 138 139 A extensive description of all namsbc namelist (parameter that have to be 140 created!) 141 142 Especially the \np{nf\_sbc}, the \mdl{sbc\_oce} module (fluxes + mean sst sss ssu 143 ssv) i.e. information required by flux computation or sea-ice 144 145 \colorbox{red}{Add nqsr = 0 / 1 replace key{\_}traqsr} 146 147 \mdl{sbc\_oce} containt the definition in memory of the 7 fields (6+runoff), add 148 a word on runoff: included in surface bc or add as lateral obc{\ldots}. 149 150 Sbcmod manage the ``providing'' (fourniture) to the ocean the 7 fields 151 152 Fluxes update only each nf{\_}sbc time step (namsbc) explain relation 153 between nf{\_}sbc and nf{\_}ice, do we define nf{\_}blk??? ? only one 154 nf{\_}sbc 155 156 Explain here all the namlist namsbc variable{\ldots}. 157 158 \colorbox{yellow}{End Miss } 159 160 The ocean model provides the following variables averaged over nf{\_}sbc 161 time-step: 125 %\colorbox{yellow}{Miss: } 126 % 127 %A extensive description of all namsbc namelist (parameter that have to be 128 %created!) 129 % 130 %Especially the \np{nf\_sbc}, the \mdl{sbc\_oce} module (fluxes + mean sst sss ssu 131 %ssv) i.e. information required by flux computation or sea-ice 132 % 133 %\mdl{sbc\_oce} containt the definition in memory of the 7 fields (6+runoff), add 134 %a word on runoff: included in surface bc or add as lateral obc{\ldots}. 135 % 136 %Sbcmod manage the ``providing'' (fourniture) to the ocean the 7 fields 137 % 138 %Fluxes update only each nf{\_}sbc time step (namsbc) explain relation 139 %between nf{\_}sbc and nf{\_}ice, do we define nf{\_}blk??? ? only one 140 %nf{\_}sbc 141 % 142 %Explain here all the namlist namsbc variable{\ldots}. 143 % 144 %\colorbox{yellow}{End Miss } 145 146 The ocean model provides the surface currents, temperature and salinity 147 averaged over \np{nf\_sbc} time-step (\ref{Tab_ssm}).The computation of the 148 mean is done in \mdl{sbcmod} module. 162 149 163 150 %-------------------------------------------------TABLE--------------------------------------------------- 164 \begin{table}[ htbp] \label{Tab_ssm}151 \begin{table}[tb] \label{Tab_ssm} 165 152 \begin{center} 166 153 \begin{tabular}{|l|l|l|l|} 167 154 \hline 168 Variable desc iption & Computer name & Units & point \\ \hline169 i-component of the surface current & ssu\_ u& $m.s^{-1}$ & U \\ \hline155 Variable description & Model variable & Units & point \\ \hline 156 i-component of the surface current & ssu\_m & $m.s^{-1}$ & U \\ \hline 170 157 j-component of the surface current & ssv\_m & $m.s^{-1}$ & V \\ \hline 171 158 Sea surface temperature & sst\_m & \r{}$K$ & T \\ \hline 172 159 Sea surface salinty & sss\_m & $psu$ & T \\ \hline 173 160 \end{tabular} 161 \caption{Ocean variables provided by the ocean to the surface module (SBC). 162 The variable are averaged over nf{\_}sbc time step, $i.e.$ the frequency of 163 computation of surface fluxes.} 174 164 \end{center} 175 165 \end{table} 176 166 %-------------------------------------------------------------------------------------------------------------- 177 167 178 The mean computation is done in sbcmod ( 179 180 \colorbox{yellow}{Penser a} mettre dans le restant l'info nf{\_}sbc ET nf{\_}sbc*rdt de sorte de 181 reinitialiser la moyenne si on change la frequence ou le pdt 182 183 NB: creer cn{\_}sbc{\_}ice (cn{\_} = character in the namelist) with 3 184 cases: 185 186 = `noice' no specific call 187 188 = `iceif ` ``ice-if'' sea ice, i.e. read observed ice-cover and modified sbc 189 bellow those area. 190 191 = `lim' LIM sea-ice model is called which update the sbc fields in ice 192 covered area 193 194 ? modify the nsbc{\_}ice variable depending of this parameter (from --1, 0 195 to 1) 196 \colorbox{yellow}{End Penser a} 168 169 170 %\colorbox{yellow}{Penser a} mettre dans le restant l'info nf{\_}sbc ET nf{\_}sbc*rdt de sorte de reinitialiser la moyenne si on change la frequence ou le pdt 171 197 172 198 173 % ================================================================ … … 203 178 \label{SBC_ana} 204 179 205 %---------------------------------------namtau - namflx-------------------------------------------------- 206 \namdisplay{namtau} 207 \namdisplay{namflx} 180 %---------------------------------------namsbc_ana-------------------------------------------------- 181 \namdisplay{namsbc_ana} 208 182 %-------------------------------------------------------------------------------------------------------------- 209 183 210 184 211 The analytical formulation of the surface boundary condition is set by 212 default. In this case, all the 6 fluxes needed by the ocean are assumed to 213 be uniform in space. They take constant values given in the namlist 214 namsbc{\_}ana : \textit{utau0}, \textit{vtau0}, \textit{qns0}, \textit{qsr0}, \textit{emp0} and \textit{emps0}. while the runoff is set to zero. In addition, 215 the wind is allowed to reach its nominal value within a given number of time 216 step (\textit{ntau000}). 217 218 If a user wants to applied a different analytical forcing, \mdl{sbcana} 219 module is the very place to do that. As an example, one can have a look to 220 the \mdl{sbc\_ana\_gyre} routine which provides the analytical forcing of the 185 The analytical formulation of the surface boundary condition is the default scheme. 186 In this case, all the six fluxes needed by the ocean are assumed to 187 be uniform in space. They take constant values given in the namelist 188 namsbc{\_}ana by the variables \np{rn\_utau0}, \np{rn\_vtau0}, \np{rn\_qns0}, 189 \np{rn\_qsr0}, and \np{rn\_emp0} (EMP$=$EMP$_S$). The runoff is set to zero. 190 In addition, the wind is allowed to reach its nominal value within a given number 191 of time steps (\np{nn\_tau000}). 192 193 If a user wants to apply a different analytical forcing, the \mdl{sbcana} 194 module can be modified to use another scheme. As an example, 195 the \mdl{sbc\_ana\_gyre} routine provides the analytical forcing for the 221 196 GYRE configuration (see GYRE configuration manual, in preparation). 222 197 … … 228 203 {Flux formulation (\mdl{sbcflx} module) } 229 204 \label{SBC_flx} 230 231 In the flux formulation (\key{sbcflx} defined), the surface boundary 205 %------------------------------------------namsbc_flx---------------------------------------------------- 206 \namdisplay{namsbc_flx} 207 %------------------------------------------------------------------------------------------------------------- 208 209 In the flux formulation (\np{ln\_flx}=true), the surface boundary 232 210 condition fields are directly read from input files. The user has to define 233 211 in the namelist namsbc{\_}flx the name of the file, the name of the variable 234 read in the file, the time frequency at which it is given , and a logical235 setting whether a time interpolation to the model time step is asked are not212 read in the file, the time frequency at which it is given (in hours), and a logical 213 setting whether a time interpolation to the model time step is required 236 214 for this field). (fld\_i namelist structure). 237 215 238 \colorbox{yellow}{ Describe the information given? }239 240 \colorbox{yellow}{ Add an info about on-line interpolation or not ? at with which scale{\ldots} }241 242 243 216 \textbf{Caution}: when the frequency is set to --12, the data are monthly 244 values. The re are assumed to be climatological values, so time interpolation217 values. These are assumed to be climatological values, so time interpolation 245 218 between December the 15$^{th}$ and January the 15$^{th}$ is done using 246 record 12 and 1219 records 12 and 1 247 220 248 221 When higher frequency is set and time interpolation is demanded, the model 249 222 will try to read the last (first) record of previous (next) year in a file 250 having the same name but a suffix {\_}prev{\_}year ( next{\_}year) being251 added . These file must only contenta single record. If they don't exist,252 the will assume that the previous year last recordis equal to the first253 record of the previousyear, and similarly, that the first record of the223 having the same name but a suffix {\_}prev{\_}year ({\_}next{\_}year) being 224 added (e.g. "{\_}1989"). These files must only contain a single record. If they don't exist, 225 the model assumes that the last record of the previous year is equal to the first 226 record of the current year, and similarly, that the first record of the 254 227 next year is equal to the last record of the current year. This will cause 255 the forcing to remain constant over the first and last half fld\_frequ 256 hours. 228 the forcing to remain constant over the first and last half fld\_frequ hours. 257 229 258 230 Note that in general, a flux formulation is used in associated with a 259 damping term to observed SST and/or SSS. See \S\ref{SBC_ssr} for its231 restoring term to observed SST and/or SSS. See \S\ref{SBC_ssr} for its 260 232 specification. 261 233 … … 271 243 using bulk formulae and atmospheric fields and ocean (and ice) variables. 272 244 273 The atmospheric fields used depends on the bulk formulae used. Two of them 274 are available : the CORE and CLIO bulk formulea. The choice is made by 275 activating the CPP key \key{sbcblk\_core} or 276 \key{sbcblk\_clio}, respectively. 277 278 \colorbox{yellow}{Note : if a sea-ice model is used then blah blah blah{\ldots}} 279 280 CORE bulk formulea 281 282 The CORE bulk formulae have been developed by \citet{LargeYeager2004}. They 283 have been design to handle the CORE forcing, a mixture of NCEP reanalysis 284 and satellite data. They use an inertial dissipative method to compute the 285 turbulent transfer coefficients (momentum, sensible heat and evaporation) 286 from the 10 meter wind speed, air temperature and specific humidity). 245 The atmospheric fields used depend on the bulk formulae used. Two bulk formulations 246 are available : the CORE and CLIO bulk formulea. The choice is made by setting to true 247 one of the following namelist variable : \np{ln\_core} and \np{ln\_clio}. 248 249 Note : in forced mode, when a sea-ice model is used, a bulk formulation have to be used. 250 Therefore the two bulk formulea provided include the computation of the fluxes over both 251 an ocean and an ice surface. 252 253 % ------------------------------------------------------------------------------------------------------------- 254 % CORE Bulk formulea 255 % ------------------------------------------------------------------------------------------------------------- 256 \subsection [CORE Bulk formulea (\np{ln\_core}=true)] 257 {CORE Bulk formulea (\np{ln\_core}=true, \mdl{sbcblk\_core})} 258 \label{SBC_blk_core} 259 %------------------------------------------namsbc_core---------------------------------------------------- 260 \namdisplay{namsbc_core} 261 %------------------------------------------------------------------------------------------------------------- 262 263 The CORE bulk formulae have been developed by \citet{LargeYeager2004}. 264 They have been designed to handle the CORE forcing, a mixture of NCEP 265 reanalysis and satellite data. They use an inertial dissipative method to compute 266 the turbulent transfer coefficients (momentum, sensible heat and evaporation) 267 from the 10 metre wind speed, air temperature and specific humidity. 268 269 Note that substituting ERA40 to NCEP reanalysis fields 270 does not require changes in the bulk formulea themself. 287 271 288 272 The required 8 input fields are: … … 293 277 \begin{tabular}{|l|l|l|l|} 294 278 \hline 295 Variable desciption & Computer name & Units& point \\ \hline296 i-component of the 10m air velocity & utau & $m.s^{-1}$ & T or U\\ \hline297 j-component of the 10m air velocity & vtau & $m.s^{-1}$ & T or V\\ \hline279 Variable desciption & Model variable & Units & point \\ \hline 280 i-component of the 10m air velocity & utau & $m.s^{-1}$ & T \\ \hline 281 j-component of the 10m air velocity & vtau & $m.s^{-1}$ & T \\ \hline 298 282 10m air temperature & tair & \r{}$K$ & T \\ \hline 299 283 Specific humidity & humi & \% & T \\ \hline … … 307 291 %-------------------------------------------------------------------------------------------------------------- 308 292 309 Note that the air velocity can be provided at either tracer ocean point or310 velocity ocean point. 311 312 \colorbox{yellow}{Explain low resolution, better to provide it at U-V, high resolution better} 313 314 \colorbox{yellow}{at T-point{\ldots} Explain why, scheme?} 315 316 \colorbox{yellow}{Add a namelist parameter to provide a switch from U/V or T (or I??) point}317 318 \colorbox{yellow}{ for utau/vtau} 319 320 CLIO bulk formulea 321 322 The CLIO bulk formulae have beendeveloped several years ago for the323 Louvain-la-neuve coupled ice-ocean model (CLIO, Goosse et al. 1997). It is a324 simpler bulk formulae that assumed the stress to be known and computes the325 radiative fluxes from a climatological cloud cover.293 Note that the air velocity is provided at a tracer ocean point, not at a velocity ocean point ($u$- and $v$-points). It is simpler and faster (less fields to be read), but it is not the recommended method when the ocean grid 294 size is the same or larger than the one of the input atmospheric fields. 295 296 % ------------------------------------------------------------------------------------------------------------- 297 % CLIO Bulk formulea 298 % ------------------------------------------------------------------------------------------------------------- 299 \subsection [CLIO Bulk formulea (\np{ln\_clio}=true)] 300 {CLIO Bulk formulea (\np{ln\_clio}=true, \mdl{sbcblk\_clio})} 301 \label{SBC_blk_clio} 302 %------------------------------------------namsbc_clio---------------------------------------------------- 303 \namdisplay{namsbc_clio} 304 %------------------------------------------------------------------------------------------------------------- 305 306 The CLIO bulk formulae were developed several years ago for the 307 Louvain-la-neuve coupled ice-ocean model (CLIO, \cite{Goosse_al_JGR99}). 308 They are simpler bulk formulae. They assume the stress to be known and 309 compute the radiative fluxes from a climatological cloud cover. 326 310 327 311 The required 7 input fields are: … … 332 316 \begin{tabular}{|l|l|l|l|} 333 317 \hline 334 Variable desciption & Computer name & Units& point \\ \hline318 Variable desciption & Model variable & Units & point \\ \hline 335 319 i-component of the ocean stress & utau & $N.m^{-2}$ & U \\ \hline 336 320 j-component of the ocean stress & vtau & $N.m^{-2}$ & V \\ \hline 337 321 Wind speed module & vatm & $m.s^{-1}$ & T \\ \hline 338 322 10m air temperature & tair & \r{}$K$ & T \\ \hline 339 S ecific humidity & humi & \% & T \\ \hline323 Specific humidity & humi & \% & T \\ \hline 340 324 Cloud cover & & \% & T \\ \hline 341 325 Total precipitation (liquid + solid) & precip & $Kg.m^{-2}.s^{-1}$ & T \\ \hline … … 346 330 %-------------------------------------------------------------------------------------------------------------- 347 331 348 As for the flux formulation, the input data informationrequired by the332 As for the flux formulation, information about the input data required by the 349 333 model is provided in the namsbc\_blk\_core or namsbc\_blk\_clio 350 namelist (via the structure fld\_i). The same assumption is made about the 351 value of the first and last record in each file. 352 334 namelist (via the structure fld\_i). The first and last record assumption is also made 335 (see \S\ref{SBC_flx}) 353 336 354 337 % ================================================================ … … 358 341 {Coupled formulation (\mdl{sbccpl} module)} 359 342 \label{SBC_cpl} 343 %------------------------------------------namsbc_cpl---------------------------------------------------- 344 \namdisplay{namsbc_cpl} 345 %------------------------------------------------------------------------------------------------------------- 360 346 361 347 In the coupled formulation of the surface boundary condition, the fluxes are … … 364 350 the atmospheric component. 365 351 352 The generalised coupled interface is under development. It should be available 353 in summer 2008. It will include the ocean interface for most of the European 354 atmospheric GCM (ARPEGE, ECHAM, ECMWF, HadAM, LMDz). 355 366 356 367 357 % ================================================================ 368 358 % Miscellanea options 369 359 % ================================================================ 370 \section{Miscellane aoptions}360 \section{Miscellaneous options} 371 361 \label{SBC_misc} 372 362 … … 377 367 {Surface restoring to observed SST and/or SSS (\mdl{sbcssr})} 378 368 \label{SBC_ssr} 379 380 In forced mode using flux formulation (default option or \key{flx} defined), a 381 feedback term \emph{must} be added to the specified surface heat flux $Q_{ns}^o$: 369 %------------------------------------------namsbc_ssr---------------------------------------------------- 370 \namdisplay{namsbc_ssr} 371 %------------------------------------------------------------------------------------------------------------- 372 373 In forced mode using a flux formulation (default option or \key{flx} defined), a 374 feedback term \emph{must} be added to the surface heat flux $Q_{ns}^o$: 382 375 \begin{equation} \label{Eq_sbc_dmp_q} 383 376 Q_{ns} = Q_{ns}^o + \frac{dQ}{dT} \left( \left. T \right|_{k=1} - SST_{Obs} \right) … … 385 378 where SST is a sea surface temperature field (observed or climatological), $T$ is 386 379 the model surface layer temperature and $\frac{dQ}{dT}$ is a negative feedback 387 coefficient usually taken equal to $-40~W.m^{-2}.$\r{}K$^{-1}$. For a $50~m$ mixed-layer depth, 388 this value corresponds to a relaxation time scale of two months. This term 389 ensures that if $T$ perfectly fits SST then $Q$ is equal to $Q_o$. 390 391 In the fresh water budget, a feedback term can also be added: 380 coefficient usually taken equal to $-40~W/m^2/K$. For a $50~m$ 381 mixed-layer depth, this value corresponds to a relaxation time scale of two months. 382 This term ensures that if $T$ perfectly matches the supplied SST, then $Q$ is 383 equal to $Q_o$. 384 385 In the fresh water budget, a feedback term can also be added. Converted into an 386 equivalent freshwater flux, it takes the following expression : 392 387 393 388 \begin{equation} \label{Eq_sbc_dmp_emp} 394 EMP = EMP_o +\gamma_s^{-1} \left(S-SSS_{Obs}\right)\left|S\right. 389 EMP = EMP_o + \gamma_s^{-1} e_{3t} \frac{ \left(\left.S\right|_{k=1}-SSS_{Obs}\right)} 390 {\left.S\right|_{k=1}} 395 391 \end{equation} 396 392 397 where EMP$_{o }$ is a net surface fresh water flux (observed, climatological or 398 atmospheric model product), \textit{SSS}$_{Obs}$is a sea surface salinity (usually a time 399 interpolation of the monthly mean PHC climatology \citep{Steele2001}, $S$ is the model 400 surface layer salinity and $\gamma_s$ is a negative feedback coefficient 401 which is provided as a namelist parameter. Unlike heat flux, there is no 402 physical justification for the feedback term in (III.4.4) as the atmosphere 403 does not care about ocean surface salinity \citep{Madec1997}. The 404 SSS restoring term can only be view as a flux correction on freshwater 405 fluxes to reduce the uncertainties we have on the observed freshwater 406 budget. 393 where EMP$_{o }$ is a net surface fresh water flux (observed, climatological or an 394 atmospheric model product), \textit{SSS}$_{Obs}$ is a sea surface salinity (usually a time 395 interpolation of the monthly mean Polar Hydrographic Climatology \citep{Steele2001}), 396 $\left.S\right|_{k=1}$ is the model surface layer salinity and $\gamma_s$ is a negative 397 feedback coefficient which is provided as a namelist parameter. Unlike heat flux, there is no 398 physical justification for the feedback term in \ref{Eq_sbc_dmp_emp} as the atmosphere 399 does not care about ocean surface salinity \citep{Madec1997}. The SSS restoring 400 term should be viewed as a flux correction on freshwater fluxes to reduce the 401 uncertainties we have on the observed freshwater budget. 407 402 408 403 % ------------------------------------------------------------------------------------------------------------- … … 411 406 \subsection{Handling of ice-covered area} 412 407 \label{SBC_ice-cover} 413 The presence of sea-ice at the top of the ocean 414 strongly modify the surface fluxes 415 416 The presence at the sea surface of an ice cover area modified all the fluxes 417 transmitted to the ocean. There is two cases whereas a sea-ice model is used 418 or not. 419 420 Without sea ice model, the information of ice-cover / open ocean is read in 421 a file (either the directly the ice-cover or the observed SST from which 422 ice-cover is deduced using a criteria on freezing point temperature). 408 409 The presence at the sea surface of an ice covered area modifies all the fluxes 410 transmitted to the ocean. There are several way to handle sea-ice in the system depending on the value of the \np{nn{\_}ice} namelist parameter. 411 \begin{description} 412 \item[nn{\_}ice = 0] there will never be sea-ice in the computational domain. This is a typical namelist value used for tropical ocean domain. The surface fluxes are simply specified for an ice-free ocean. No specific things are done for sea-ice. 413 \item[nn{\_}ice = 1] sea-ice can exist in the computational domain, but no sea-ice model is used. An observed ice covered area is read in a file. Below this area, the SST is restored to the freezing point and the heat fluxes are set to $-4~W/m^2$ ($-2~W/m^2$) in the northern (southern) hemisphere. The associated modification of the freshwater fluxes are done in such a way that the change in buoyancy fluxes remains zero. This prevents deep convection to occur when trying to reach the freezing point (and so ice covered area condition) while the SSS is too large. This manner of managing sea-ice area, just by using si IF case, is usually referred as the \textit{ice-if} model. It can be found in the \mdl{sbcice{\_}if} module. 414 \item[nn{\_}ice = 2 or more] A full sea ice model is used. This model computes the ice-ocean fluxes, that are combined with the air-sea fluxes using the ice fraction of each model cell to provide the surface ocean fluxes. Note that the activation of a sea-ice model is is done by defining a CPP key (\key{lim2} or \key{lim3}). The activation automatically ovewrite the read value of nn{\_}ice to its appropriate value ($i.e.$ $2$ for LIM-2 and $3$ for LIM-3). 415 \end{description} 416 417 % {Description of Ice-ocean interface to be added here or in LIM 2 and 3 doc ?} 423 418 424 419 % ------------------------------------------------------------------------------------------------------------- … … 428 423 {Addition of river runoffs (\mdl{sbcrnf})} 429 424 \label{SBC_rnf} 425 %------------------------------------------namsbc_rnf---------------------------------------------------- 426 \namdisplay{namsbc_rnf} 427 %------------------------------------------------------------------------------------------------------------- 430 428 431 429 It is convenient to introduce the river runoff in the model as a surface 432 fresh water flux es. \colorbox{yellow}{{\ldots} blah blah{\ldots}.}430 fresh water flux. 433 431 434 432 \colorbox{yellow}{Nevertheless, Pb of vertical resolution and increase of Kz in vicinity of } … … 444 442 {Freshwater budget control (\mdl{sbcfwb})} 445 443 \label{SBC_fwb} 446 %--------------------------------------------namfwb-------------------------------------------------------- 447 \namdisplay{namfwb} 448 %-------------------------------------------------------------------------------------------------------------- 449 450 To be written latter... 444 445 To be written later... 451 446 452 447 \gmcomment{The descrition of the technique used to control the freshwater budget has to be added here}
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