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branches/2016/dev_INGV_UKMO_2016/DOC/TexFiles/Chapters/Chap_SBC.tex
r5120 r7351 1 % ================================================================ 2 % Chapter � Surface Boundary Condition (SBC, ISF, ICB) 1 \documentclass[NEMO_book]{subfiles} 2 \begin{document} 3 % ================================================================ 4 % Chapter —— Surface Boundary Condition (SBC, ISF, ICB) 3 5 % ================================================================ 4 6 \chapter{Surface Boundary Condition (SBC, ISF, ICB) } … … 17 19 \item the two components of the surface ocean stress $\left( {\tau _u \;,\;\tau _v} \right)$ 18 20 \item the incoming solar and non solar heat fluxes $\left( {Q_{ns} \;,\;Q_{sr} } \right)$ 19 \item the surface freshwater budget $\left( {\textit{emp},\;\textit{emp}_S } \right)$ 21 \item the surface freshwater budget $\left( {\textit{emp}} \right)$ 22 \item the surface salt flux associated with freezing/melting of seawater $\left( {\textit{sfx}} \right)$ 20 23 \end{itemize} 21 24 plus an optional field: … … 27 30 are controlled by namelist \ngn{namsbc} variables: an analytical formulation (\np{ln\_ana}~=~true), 28 31 a flux formulation (\np{ln\_flx}~=~true), a bulk formulae formulation (CORE 29 (\np{ln\_ core}~=~true), CLIO (\np{ln\_clio}~=~true) or MFS32 (\np{ln\_blk\_core}~=~true), CLIO (\np{ln\_blk\_clio}~=~true) or MFS 30 33 \footnote { Note that MFS bulk formulae compute fluxes only for the ocean component} 31 (\np{ln\_mfs}~=~true) bulk formulae) and a coupled 32 formulation (exchanges with a atmospheric model via the OASIS coupler) 33 (\np{ln\_cpl}~=~true). When used, the atmospheric pressure forces both 34 ocean and ice dynamics (\np{ln\_apr\_dyn}~=~true). 35 The frequency at which the six or seven fields have to be updated is the \np{nn\_fsbc} 36 namelist parameter. 34 (\np{ln\_blk\_mfs}~=~true) bulk formulae) and a coupled or mixed forced/coupled formulation 35 (exchanges with a atmospheric model via the OASIS coupler) (\np{ln\_cpl} or \np{ln\_mixcpl}~=~true). 36 When used ($i.e.$ \np{ln\_apr\_dyn}~=~true), the atmospheric pressure forces both ocean and ice dynamics. 37 38 The frequency at which the forcing fields have to be updated is given by the \np{nn\_fsbc} namelist parameter. 37 39 When the fields are supplied from data files (flux and bulk formulations), the input fields 38 need not be supplied on the model grid. 40 need not be supplied on the model grid. Instead a file of coordinates and weights can 39 41 be supplied which maps the data from the supplied grid to the model points 40 42 (so called "Interpolation on the Fly", see \S\ref{SBC_iof}). … … 42 44 can be masked to avoid spurious results in proximity of the coasts as large sea-land gradients characterize 43 45 most of the atmospheric variables. 46 44 47 In addition, the resulting fields can be further modified using several namelist options. 45 These options control the rotation of vector components supplied relative to an east-north 46 coordinate system onto the local grid directions in the model; the addition of a surface 47 restoring term to observed SST and/or SSS (\np{ln\_ssr}~=~true); the modification of fluxes 48 below ice-covered areas (using observed ice-cover or a sea-ice model) 49 (\np{nn\_ice}~=~0,1, 2 or 3); the addition of river runoffs as surface freshwater 50 fluxes or lateral inflow (\np{ln\_rnf}~=~true); the addition of isf melting as lateral inflow (parameterisation) 51 (\np{nn\_isf}~=~2 or 3 and \np{ln\_isfcav}~=~false) or as surface flux at the land-ice ocean interface 52 (\np{nn\_isf}~=~1 or 4 and \np{ln\_isfcav}~=~true); 53 the addition of a freshwater flux adjustment in order to avoid a mean sea-level drift (\np{nn\_fwb}~=~0,~1~or~2); the 54 transformation of the solar radiation (if provided as daily mean) into a diurnal 55 cycle (\np{ln\_dm2dc}~=~true); and a neutral drag coefficient can be read from an external wave 56 model (\np{ln\_cdgw}~=~true). The latter option is possible only in case core or mfs bulk formulas are selected. 48 These options control 49 \begin{itemize} 50 \item the rotation of vector components supplied relative to an east-north 51 coordinate system onto the local grid directions in the model ; 52 \item the addition of a surface restoring term to observed SST and/or SSS (\np{ln\_ssr}~=~true) ; 53 \item the modification of fluxes below ice-covered areas (using observed ice-cover or a sea-ice model) (\np{nn\_ice}~=~0,1, 2 or 3) ; 54 \item the addition of river runoffs as surface freshwater fluxes or lateral inflow (\np{ln\_rnf}~=~true) ; 55 \item the addition of isf melting as lateral inflow (parameterisation) or as fluxes applied at the land-ice ocean interface (\np{ln\_isf}) ; 56 \item the addition of a freshwater flux adjustment in order to avoid a mean sea-level drift (\np{nn\_fwb}~=~0,~1~or~2) ; 57 \item the transformation of the solar radiation (if provided as daily mean) into a diurnal cycle (\np{ln\_dm2dc}~=~true) ; 58 and a neutral drag coefficient can be read from an external wave model (\np{ln\_cdgw}~=~true). 59 \end{itemize} 60 The latter option is possible only in case core or mfs bulk formulas are selected. 57 61 58 62 In this chapter, we first discuss where the surface boundary condition appears in the … … 73 77 74 78 The surface ocean stress is the stress exerted by the wind and the sea-ice 75 on the ocean. The two components of stress are assumed to be interpolated 76 onto the ocean mesh, $i.e.$ resolved onto the model (\textbf{i},\textbf{j}) direction 77 at $u$- and $v$-points They are applied as a surface boundary condition of the 78 computation of the momentum vertical mixing trend (\mdl{dynzdf} module) : 79 \begin{equation} \label{Eq_sbc_dynzdf} 80 \left.{\left( {\frac{A^{vm} }{e_3 }\ \frac{\partial \textbf{U}_h}{\partial k}} \right)} \right|_{z=1} 81 = \frac{1}{\rho _o} \binom{\tau _u}{\tau _v } 82 \end{equation} 83 where $(\tau _u ,\;\tau _v )=(utau,vtau)$ are the two components of the wind 84 stress vector in the $(\textbf{i},\textbf{j})$ coordinate system. 79 on the ocean. It is applied in \mdl{dynzdf} module as a surface boundary condition of the 80 computation of the momentum vertical mixing trend (see \eqref{Eq_dynzdf_sbc} in \S\ref{DYN_zdf}). 81 As such, it has to be provided as a 2D vector interpolated 82 onto the horizontal velocity ocean mesh, $i.e.$ resolved onto the model 83 (\textbf{i},\textbf{j}) direction at $u$- and $v$-points. 85 84 86 85 The surface heat flux is decomposed into two parts, a non solar and a solar heat 87 86 flux, $Q_{ns}$ and $Q_{sr}$, respectively. The former is the non penetrative part 88 of the heat flux ($i.e.$ the sum of sensible, latent and long wave heat fluxes). 89 It is applied as a surface boundary condition trend of the first level temperature 90 time evolution equation (\mdl{trasbc} module). 91 \begin{equation} \label{Eq_sbc_trasbc_q} 92 \frac{\partial T}{\partial t}\equiv \cdots \;+\;\left. {\frac{Q_{ns} }{\rho 93 _o \;C_p \;e_{3t} }} \right|_{k=1} \quad 94 \end{equation} 95 $Q_{sr}$ is the penetrative part of the heat flux. It is applied as a 3D 96 trends of the temperature equation (\mdl{traqsr} module) when \np{ln\_traqsr}=True. 97 98 \begin{equation} \label{Eq_sbc_traqsr} 99 \frac{\partial T}{\partial t}\equiv \cdots \;+\frac{Q_{sr} }{\rho_o C_p \,e_{3t} }\delta _k \left[ {I_w } \right] 100 \end{equation} 101 where $I_w$ is a non-dimensional function that describes the way the light 102 penetrates inside the water column. It is generally a sum of decreasing 103 exponentials (see \S\ref{TRA_qsr}). 104 105 The surface freshwater budget is provided by fields: \textit{emp} and $\textit{emp}_S$ which 106 may or may not be identical. Indeed, a surface freshwater flux has two effects: 107 it changes the volume of the ocean and it changes the surface concentration of 108 salt (and other tracers). Therefore it appears in the sea surface height as a volume 109 flux, \textit{emp} (\textit{dynspg\_xxx} modules), and in the salinity time evolution equations 110 as a concentration/dilution effect, 111 $\textit{emp}_{S}$ (\mdl{trasbc} module). 112 \begin{equation} \label{Eq_trasbc_emp} 113 \begin{aligned} 114 &\frac{\partial \eta }{\partial t}\equiv \cdots \;+\;\textit{emp}\quad \\ 115 \\ 116 &\frac{\partial S}{\partial t}\equiv \cdots \;+\left. {\frac{\textit{emp}_S \;S}{e_{3t} }} \right|_{k=1} \\ 117 \end{aligned} 118 \end{equation} 119 120 In the real ocean, $\textit{emp}=\textit{emp}_S$ and the ocean salt content is conserved, 121 but it exist several numerical reasons why this equality should be broken. 122 For example, when the ocean is coupled to a sea-ice model, the water exchanged between 123 ice and ocean is slightly salty (mean sea-ice salinity is $\sim $\textit{4 psu}). In this case, 124 $\textit{emp}_{S}$ take into account both concentration/dilution effect associated with 125 freezing/melting and the salt flux between ice and ocean, while \textit{emp} is 126 only the volume flux. In addition, in the current version of \NEMO, the sea-ice is 127 assumed to be above the ocean (the so-called levitating sea-ice). Freezing/melting does 128 not change the ocean volume (no impact on \textit{emp}) but it modifies the SSS. 129 %gm \colorbox{yellow}{(see {\S} on LIM sea-ice model)}. 130 131 Note that SST can also be modified by a freshwater flux. Precipitation (in 132 particular solid precipitation) may have a temperature significantly different from 133 the SST. Due to the lack of information about the temperature of 134 precipitation, we assume it is equal to the SST. Therefore, no 135 concentration/dilution term appears in the temperature equation. It has to 136 be emphasised that this absence does not mean that there is no heat flux 137 associated with precipitation! Precipitation can change the ocean volume and thus the 138 ocean heat content. It is therefore associated with a heat flux (not yet 139 diagnosed in the model) \citep{Roullet_Madec_JGR00}). 87 of the heat flux ($i.e.$ the sum of sensible, latent and long wave heat fluxes 88 plus the heat content of the mass exchange with the atmosphere and sea-ice). 89 It is applied in \mdl{trasbc} module as a surface boundary condition trend of 90 the first level temperature time evolution equation (see \eqref{Eq_tra_sbc} 91 and \eqref{Eq_tra_sbc_lin} in \S\ref{TRA_sbc}). 92 The latter is the penetrative part of the heat flux. It is applied as a 3D 93 trends of the temperature equation (\mdl{traqsr} module) when \np{ln\_traqsr}=\textit{true}. 94 The way the light penetrates inside the water column is generally a sum of decreasing 95 exponentials (see \S\ref{TRA_qsr}). 96 97 The surface freshwater budget is provided by the \textit{emp} field. 98 It represents the mass flux exchanged with the atmosphere (evaporation minus precipitation) 99 and possibly with the sea-ice and ice shelves (freezing minus melting of ice). 100 It affects both the ocean in two different ways: 101 $(i)$ it changes the volume of the ocean and therefore appears in the sea surface height 102 equation as a volume flux, and 103 $(ii)$ it changes the surface temperature and salinity through the heat and salt contents 104 of the mass exchanged with the atmosphere, the sea-ice and the ice shelves. 105 140 106 141 107 %\colorbox{yellow}{Miss: } … … 157 123 % 158 124 %Explain here all the namlist namsbc variable{\ldots}. 125 % 126 % explain : use or not of surface currents 159 127 % 160 128 %\colorbox{yellow}{End Miss } 161 129 162 The ocean model provides the surface currents, temperature and salinity 163 averaged over \np{nf\_sbc} time-step (\ref{Tab_ssm}).The computation of the 164 mean is done in \mdl{sbcmod} module. 130 The ocean model provides, at each time step, to the surface module (\mdl{sbcmod}) 131 the surface currents, temperature and salinity. 132 These variables are averaged over \np{nn\_fsbc} time-step (\ref{Tab_ssm}), 133 and it is these averaged fields which are used to computes the surface fluxes 134 at a frequency of \np{nn\_fsbc} time-step. 135 165 136 166 137 %-------------------------------------------------TABLE--------------------------------------------------- … … 175 146 \caption{ \label{Tab_ssm} 176 147 Ocean variables provided by the ocean to the surface module (SBC). 177 The variable are averaged over n f{\_}sbc time step, $i.e.$ the frequency of178 computation of surface fluxes.}148 The variable are averaged over nn{\_}fsbc time step, 149 $i.e.$ the frequency of computation of surface fluxes.} 179 150 \end{center} \end{table} 180 151 %-------------------------------------------------------------------------------------------------------------- … … 459 430 %-------------------------------------------------------------------------------------------------------------- 460 431 461 In some circumstances it may be useful to avoid calculating the 3D temperature, salinity and velocity fields and simply read them in from a previous run.462 Options are defined through the \ngn{namsbc\_sas} namelist variables. 432 In some circumstances it may be useful to avoid calculating the 3D temperature, salinity and velocity fields 433 and simply read them in from a previous run or receive them from OASIS. 463 434 For example: 464 435 465 \begin{ enumerate}466 \item Multiple runs of the model are required in code development to see the affect of different algorithms in436 \begin{itemize} 437 \item Multiple runs of the model are required in code development to see the effect of different algorithms in 467 438 the bulk formulae. 468 439 \item The effect of different parameter sets in the ice model is to be examined. 469 \end{enumerate} 440 \item Development of sea-ice algorithms or parameterizations. 441 \item spinup of the iceberg floats 442 \item ocean/sea-ice simulation with both media running in parallel (\np{ln\_mixcpl}~=~\textit{true}) 443 \end{itemize} 470 444 471 445 The StandAlone Surface scheme provides this utility. 446 Its options are defined through the \ngn{namsbc\_sas} namelist variables. 472 447 A new copy of the model has to be compiled with a configuration based on ORCA2\_SAS\_LIM. 473 448 However no namelist parameters need be changed from the settings of the previous run (except perhaps nn{\_}date0) … … 475 450 Routines replaced are: 476 451 477 \begin{enumerate} 478 \item \mdl{nemogcm} 479 480 This routine initialises the rest of the model and repeatedly calls the stp time stepping routine (step.F90) 452 \begin{itemize} 453 \item \mdl{nemogcm} : This routine initialises the rest of the model and repeatedly calls the stp time stepping routine (step.F90) 481 454 Since the ocean state is not calculated all associated initialisations have been removed. 482 \item \mdl{step} 483 484 The main time stepping routine now only needs to call the sbc routine (and a few utility functions). 485 \item \mdl{sbcmod} 486 487 This has been cut down and now only calculates surface forcing and the ice model required. New surface modules 455 \item \mdl{step} : The main time stepping routine now only needs to call the sbc routine (and a few utility functions). 456 \item \mdl{sbcmod} : This has been cut down and now only calculates surface forcing and the ice model required. New surface modules 488 457 that can function when only the surface level of the ocean state is defined can also be added (e.g. icebergs). 489 \item \mdl{daymod} 490 491 No ocean restarts are read or written (though the ice model restarts are retained), so calls to restart functions 458 \item \mdl{daymod} : No ocean restarts are read or written (though the ice model restarts are retained), so calls to restart functions 492 459 have been removed. This also means that the calendar cannot be controlled by time in a restart file, so the user 493 460 must make sure that nn{\_}date0 in the model namelist is correct for his or her purposes. 494 \item \mdl{stpctl} 495 496 Since there is no free surface solver, references to it have been removed from \rou{stp\_ctl} module. 497 \item \mdl{diawri} 498 499 All 3D data have been removed from the output. The surface temperature, salinity and velocity components (which 461 \item \mdl{stpctl} : Since there is no free surface solver, references to it have been removed from \rou{stp\_ctl} module. 462 \item \mdl{diawri} : All 3D data have been removed from the output. The surface temperature, salinity and velocity components (which 500 463 have been read in) are written along with relevant forcing and ice data. 501 \end{ enumerate}464 \end{itemize} 502 465 503 466 One new routine has been added: 504 467 505 \begin{enumerate} 506 \item \mdl{sbcsas} 507 This module initialises the input files needed for reading temperature, salinity and velocity arrays at the surface. 468 \begin{itemize} 469 \item \mdl{sbcsas} : This module initialises the input files needed for reading temperature, salinity and velocity arrays at the surface. 508 470 These filenames are supplied in namelist namsbc{\_}sas. Unfortunately because of limitations with the \mdl{iom} module, 509 471 the full 3D fields from the mean files have to be read in and interpolated in time, before using just the top level. 510 472 Since fldread is used to read in the data, Interpolation on the Fly may be used to change input data resolution. 511 \end{enumerate} 473 \end{itemize} 474 475 476 % Missing the description of the 2 following variables: 477 % ln_3d_uve = .true. ! specify whether we are supplying a 3D u,v and e3 field 478 % ln_read_frq = .false. ! specify whether we must read frq or not 479 480 512 481 513 482 % ================================================================ … … 625 594 or larger than the one of the input atmospheric fields. 626 595 596 The \np{sn\_wndi}, \np{sn\_wndj}, \np{sn\_qsr}, \np{sn\_qlw}, \np{sn\_tair}, \np{sn\_humi}, 597 \np{sn\_prec}, \np{sn\_snow}, \np{sn\_tdif} parameters describe the fields 598 and the way they have to be used (spatial and temporal interpolations). 599 600 \np{cn\_dir} is the directory of location of bulk files 601 \np{ln\_taudif} is the flag to specify if we use Hight Frequency (HF) tau information (.true.) or not (.false.) 602 \np{rn\_zqt}: is the height of humidity and temperature measurements (m) 603 \np{rn\_zu}: is the height of wind measurements (m) 604 605 Three multiplicative factors are availables : 606 \np{rn\_pfac} and \np{rn\_efac} allows to adjust (if necessary) the global freshwater budget 607 by increasing/reducing the precipitations (total and snow) and or evaporation, respectively. 608 The third one,\np{rn\_vfac}, control to which extend the ice/ocean velocities are taken into account 609 in the calculation of surface wind stress. Its range should be between zero and one, 610 and it is recommended to set it to 0. 611 627 612 % ------------------------------------------------------------------------------------------------------------- 628 613 % CLIO Bulk formulea … … 720 705 are sent to the atmospheric component. 721 706 722 A generalised coupled interface has been developed. It is currently interfaced with OASIS 3 723 (\key{oasis3}) and does not support OASIS 4 724 \footnote{The \key{oasis4} exist. It activates portion of the code that are still under development.}. 707 A generalised coupled interface has been developed. 708 It is currently interfaced with OASIS-3-MCT (\key{oasis3}). 725 709 It has been successfully used to interface \NEMO to most of the European atmospheric 726 710 GCM (ARPEGE, ECHAM, ECMWF, HadAM, HadGAM, LMDz), … … 787 771 \label{SBC_tide} 788 772 789 A module is available to use the tidal potential forcing and is activated with with \key{tide}. 790 791 792 %------------------------------------------nam_tide---------------------------------------------------- 773 %------------------------------------------nam_tide--------------------------------------- 793 774 \namdisplay{nam_tide} 794 %------------------------------------------------------------------------------------------------------------- 795 796 Concerning the tidal potential, some parameters are available in namelist \ngn{nam\_tide}: 775 %----------------------------------------------------------------------------------------- 776 777 A module is available to compute the tidal potential and use it in the momentum equation. 778 This option is activated when \key{tide} is defined. 779 780 Some parameters are available in namelist \ngn{nam\_tide}: 797 781 798 782 - \np{ln\_tide\_pot} activate the tidal potential forcing … … 801 785 802 786 - \np{clname} is the name of constituent 803 804 787 805 788 The tide is generated by the forces of gravity ot the Earth-Moon and Earth-Sun sytem; … … 958 941 \namdisplay{namsbc_isf} 959 942 %-------------------------------------------------------------------------------------------------------- 960 Namelist variable in \ngn{namsbc}, \np{nn\_isf}, control the kind ofice shelf representation used.943 Namelist variable in \ngn{namsbc}, \np{nn\_isf}, controls the ice shelf representation used. 961 944 \begin{description} 962 945 \item[\np{nn\_isf}~=~1] 963 The ice shelf cavity is represented. The fwf and heat flux are computed. 964 Full description, sensitivity and validation in preparation. 946 The ice shelf cavity is represented (\np{ln\_isfcav}~=~true needed). The fwf and heat flux are computed. 947 Two different bulk formula are available: 948 \begin{description} 949 \item[\np{nn\_isfblk}~=~1] 950 The bulk formula used to compute the melt is based the one described in \citet{Hunter2006}. 951 This formulation is based on a balance between the upward ocean heat flux and the latent heat flux at the ice shelf base. 952 953 \item[\np{nn\_isfblk}~=~2] 954 The bulk formula used to compute the melt is based the one described in \citet{Jenkins1991}. 955 This formulation is based on a 3 equations formulation (a heat flux budget, a salt flux budget 956 and a linearised freezing point temperature equation). 957 \end{description} 958 959 For this 2 bulk formulations, there are 3 different ways to compute the exchange coeficient: 960 \begin{description} 961 \item[\np{nn\_gammablk~=~0~}] 962 The salt and heat exchange coefficients are constant and defined by \np{rn\_gammas0} and \np{rn\_gammat0} 963 964 \item[\np{nn\_gammablk~=~1~}] 965 The salt and heat exchange coefficients are velocity dependent and defined as $\np{rn\_gammas0} \times u_{*}$ and $\np{rn\_gammat0} \times u_{*}$ 966 where $u_{*}$ is the friction velocity in the top boundary layer (ie first \np{rn\_hisf\_tbl} meters). 967 See \citet{Jenkins2010} for all the details on this formulation. 968 969 \item[\np{nn\_gammablk~=~2~}] 970 The salt and heat exchange coefficients are velocity and stability dependent and defined as 971 $\gamma_{T,S} = \frac{u_{*}}{\Gamma_{Turb} + \Gamma^{T,S}_{Mole}}$ 972 where $u_{*}$ is the friction velocity in the top boundary layer (ie first \np{rn\_hisf\_tbl} meters), 973 $\Gamma_{Turb}$ the contribution of the ocean stability and 974 $\Gamma^{T,S}_{Mole}$ the contribution of the molecular diffusion. 975 See \citet{Holland1999} for all the details on this formulation. 976 \end{description} 965 977 966 978 \item[\np{nn\_isf}~=~2] … … 968 980 The fwf is distributed along the ice shelf edge between the depth of the average grounding line (GL) 969 981 (\np{sn\_depmax\_isf}) and the base of the ice shelf along the calving front (\np{sn\_depmin\_isf}) as in (\np{nn\_isf}~=~3). 970 Furthermore the fwf iscomputed using the \citet{Beckmann2003} parameterisation of isf melting.982 Furthermore the fwf and heat flux are computed using the \citet{Beckmann2003} parameterisation of isf melting. 971 983 The effective melting length (\np{sn\_Leff\_isf}) is read from a file. 972 984 973 985 \item[\np{nn\_isf}~=~3] 974 986 A simple parameterisation of isf is used. The ice shelf cavity is not represented. 975 The fwf (\np{sn\_rnfisf}) is distributed along the ice shelf edge between the depth of the average grounding line (GL)976 (\np{sn\_depmax\_isf}) and the base of the ice shelf along the calving front (\np{sn\_depmin\_isf}). 977 Full description, sensitivity and validation in preparation.987 The fwf (\np{sn\_rnfisf}) is prescribed and distributed along the ice shelf edge between the depth of the average grounding line (GL) 988 (\np{sn\_depmax\_isf}) and the base of the ice shelf along the calving front (\np{sn\_depmin\_isf}). 989 The heat flux ($Q_h$) is computed as $Q_h = fwf \times L_f$. 978 990 979 991 \item[\np{nn\_isf}~=~4] 980 The ice shelf cavity is represented. However, the fwf (\np{sn\_fwfisf}) and heat flux (\np{sn\_qisf}) are981 not computed but specified from file. 992 The ice shelf cavity is opened (\np{ln\_isfcav}~=~true needed). However, the fwf is not computed but specified from file \np{sn\_fwfisf}). 993 The heat flux ($Q_h$) is computed as $Q_h = fwf \times L_f$.\\ 982 994 \end{description} 983 995 984 \np{nn\_isf}~=~1 and \np{nn\_isf}~=~2 compute a melt rate based on the water masse properties, ocean velocities and depth. 985 This flux is thus highly dependent of the model resolution (horizontal and vertical), realism of the water masse onto the shelf ... 986 987 \np{nn\_isf}~=~3 and \np{nn\_isf}~=~4 read the melt rate and heat flux from a file. You have total control of the fwf scenario. 988 989 This can be usefull if the water masses on the shelf are not realistic or the resolution (horizontal/vertical) are too 990 coarse to have realistic melting or for sensitivity studies where you want to control your input. 991 Full description, sensitivity and validation in preparation. 992 993 There is 2 ways to apply the fwf to NEMO. The first possibility (\np{ln\_divisf}~=~false) applied the fwf 994 and heat flux directly on the salinity and temperature tendancy. The second possibility (\np{ln\_divisf}~=~true) 995 apply the fwf as for the runoff fwf (see \S\ref{SBC_rnf}). The mass/volume addition due to the ice shelf melting is, 996 at each relevant depth level, added to the horizontal divergence (\textit{hdivn}) in the subroutine \rou{sbc\_isf\_div} 997 (called from \mdl{divcur}). 996 997 $\bullet$ \np{nn\_isf}~=~1 and \np{nn\_isf}~=~2 compute a melt rate based on the water mass properties, ocean velocities and depth. 998 This flux is thus highly dependent of the model resolution (horizontal and vertical), realism of the water masses onto the shelf ...\\ 999 1000 1001 $\bullet$ \np{nn\_isf}~=~3 and \np{nn\_isf}~=~4 read the melt rate from a file. You have total control of the fwf forcing. 1002 This can be usefull if the water masses on the shelf are not realistic or the resolution (horizontal/vertical) are too 1003 coarse to have realistic melting or for studies where you need to control your heat and fw input.\\ 1004 1005 A namelist parameters control over how many meters the heat and fw fluxes are spread. 1006 \np{rn\_hisf\_tbl}] is the top boundary layer thickness as defined in \citet{Losch2008}. 1007 This parameter is only used if \np{nn\_isf}~=~1 or \np{nn\_isf}~=~4 1008 1009 If \np{rn\_hisf\_tbl} = 0., the fluxes are put in the top level whatever is its tickness. 1010 1011 If \np{rn\_hisf\_tbl} $>$ 0., the fluxes are spread over the first \np{rn\_hisf\_tbl} m (ie over one or several cells).\\ 1012 1013 The ice shelf melt is implemented as a volume flux with in the same way as for the runoff. 1014 The fw addition due to the ice shelf melting is, at each relevant depth level, added to the horizontal divergence 1015 (\textit{hdivn}) in the subroutine \rou{sbc\_isf\_div}, called from \mdl{divcur}. 1016 See the runoff section \ref{SBC_rnf} for all the details about the divergence correction. 1017 1018 1019 \section{ Ice sheet coupling} 1020 \label{SBC_iscpl} 1021 %------------------------------------------namsbc_iscpl---------------------------------------------------- 1022 \namdisplay{namsbc_iscpl} 1023 %-------------------------------------------------------------------------------------------------------- 1024 Ice sheet/ocean coupling is done through file exchange at the restart step. NEMO, at each restart step, 1025 read the bathymetry and ice shelf draft variable in a netcdf file. 1026 If \np{ln\_iscpl = ~true}, the isf draft is assume to be different at each restart step 1027 with potentially some new wet/dry cells due to the ice sheet dynamics/thermodynamics. 1028 The wetting and drying scheme applied on the restart is very simple and described below for the 6 different cases: 1029 \begin{description} 1030 \item[Thin a cell down:] 1031 T/S/ssh are unchanged and U/V in the top cell are corrected to keep the barotropic transport (bt) constant ($bt_b=bt_n$). 1032 \item[Enlarge a cell:] 1033 See case "Thin a cell down" 1034 \item[Dry a cell:] 1035 mask, T/S, U/V and ssh are set to 0. Furthermore, U/V into the water column are modified to satisfy ($bt_b=bt_n$). 1036 \item[Wet a cell:] 1037 mask is set to 1, T/S is extrapolated from neighbours, $ssh_n = ssh_b$ and U/V set to 0. If no neighbours along i,j and k, T/S/U/V and mask are set to 0. 1038 \item[Dry a column:] 1039 mask, T/S, U/V are set to 0 everywhere in the column and ssh set to 0. 1040 \item[Wet a column:] 1041 set mask to 1, T/S is extrapolated from neighbours, ssh is extrapolated from neighbours and U/V set to 0. If no neighbour, T/S/U/V and mask set to 0. 1042 \end{description} 1043 The extrapolation is call \np{nn\_drown} times. It means that if the grounding line retreat by more than \np{nn\_drown} cells between 2 coupling steps, 1044 the code will be unable to fill all the new wet cells properly. The default number is set up for the MISOMIP idealised experiments.\\ 1045 This coupling procedure is able to take into account grounding line and calving front migration. However, it is a non-conservative processe. 1046 This could lead to a trend in heat/salt content and volume. In order to remove the trend and keep the conservation level as close to 0 as possible, 1047 a simple conservation scheme is available with \np{ln\_hsb = ~true}. The heat/salt/vol. gain/loss is diagnose, as well as the location. 1048 Based on what is done on sbcrnf to prescribed a source of heat/salt/vol., the heat/salt/vol. gain/loss is removed/added, 1049 over a period of \np{rn\_fiscpl} time step, into the system. 1050 So after \np{rn\_fiscpl} time step, all the heat/salt/vol. gain/loss due to extrapolation process is canceled.\\ 1051 1052 As the before and now fields are not compatible (modification of the geometry), the restart time step is prescribed to be an euler time step instead of a leap frog and $fields_b = fields_n$. 998 1053 % 999 1054 % ================================================================ 1000 1055 % Handling of icebergs 1001 1056 % ================================================================ 1002 \section{ Handling of icebergs (ICB)}1057 \section{Handling of icebergs (ICB)} 1003 1058 \label{ICB_icebergs} 1004 1059 %------------------------------------------namberg---------------------------------------------------- … … 1006 1061 %------------------------------------------------------------------------------------------------------------- 1007 1062 1008 Icebergs are modelled as lagrangian particles in NEMO. 1009 Their physical behaviour is controlled by equations as described in \citet{Martin_Adcroft_OM10} ). 1010 (Note that the authors kindly provided a copy of their code to act as a basis for implementation in NEMO.) 1011 Icebergs are initially spawned into one of ten classes which have specific mass and thickness as described in the \ngn{namberg} namelist: 1063 Icebergs are modelled as lagrangian particles in NEMO \citep{Marsh_GMD2015}. 1064 Their physical behaviour is controlled by equations as described in \citet{Martin_Adcroft_OM10} ). 1065 (Note that the authors kindly provided a copy of their code to act as a basis for implementation in NEMO). 1066 Icebergs are initially spawned into one of ten classes which have specific mass and thickness as described 1067 in the \ngn{namberg} namelist: 1012 1068 \np{rn\_initial\_mass} and \np{rn\_initial\_thickness}. 1013 1069 Each class has an associated scaling (\np{rn\_mass\_scaling}), which is an integer representing how many icebergs … … 1079 1135 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1080 1136 \begin{figure}[!t] \begin{center} 1081 \includegraphics[width=0.8\textwidth]{ ./TexFiles/Figures/Fig_SBC_diurnal.pdf}1137 \includegraphics[width=0.8\textwidth]{Fig_SBC_diurnal} 1082 1138 \caption{ \label{Fig_SBC_diurnal} 1083 1139 Example of recontruction of the diurnal cycle variation of short wave flux … … 1112 1168 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1113 1169 \begin{figure}[!t] \begin{center} 1114 \includegraphics[width=0.7\textwidth]{ ./TexFiles/Figures/Fig_SBC_dcy.pdf}1170 \includegraphics[width=0.7\textwidth]{Fig_SBC_dcy} 1115 1171 \caption{ \label{Fig_SBC_dcy} 1116 1172 Example of recontruction of the diurnal cycle variation of short wave flux … … 1193 1249 The presence at the sea surface of an ice covered area modifies all the fluxes 1194 1250 transmitted to the ocean. There are several way to handle sea-ice in the system 1195 depending on the value of the \np{nn {\_}ice} namelist parameter.1251 depending on the value of the \np{nn\_ice} namelist parameter found in \ngn{namsbc} namelist. 1196 1252 \begin{description} 1197 1253 \item[nn{\_}ice = 0] there will never be sea-ice in the computational domain. … … 1268 1324 % ------------------------------------------------------------------------------------------------------------- 1269 1325 \subsection [Neutral drag coefficient from external wave model (\textit{sbcwave})] 1270 1326 {Neutral drag coefficient from external wave model (\mdl{sbcwave})} 1271 1327 \label{SBC_wave} 1272 1328 %------------------------------------------namwave---------------------------------------------------- 1273 1329 \namdisplay{namsbc_wave} 1274 1330 %------------------------------------------------------------------------------------------------------------- 1275 \begin{description} 1276 1277 \item [??] In order to read a neutral drag coeff, from an external data source (i.e. a wave model), the 1278 logical variable \np{ln\_cdgw} 1279 in $namsbc$ namelist must be defined ${.true.}$. 1331 1332 In order to read a neutral drag coeff, from an external data source ($i.e.$ a wave model), the 1333 logical variable \np{ln\_cdgw} in \ngn{namsbc} namelist must be set to \textit{true}. 1280 1334 The \mdl{sbcwave} module containing the routine \np{sbc\_wave} reads the 1281 1335 namelist \ngn{namsbc\_wave} (for external data names, locations, frequency, interpolation and all 1282 1336 the miscellanous options allowed by Input Data generic Interface see \S\ref{SBC_input}) 1283 and a 2D field of neutral drag coefficient. Then using the routine 1284 TURB\_CORE\_1Z or TURB\_CORE\_2Z, and starting from the neutral drag coefficent provided, the drag coefficient is computed according 1285 to stable/unstable conditions of the air-sea interface following \citet{Large_Yeager_Rep04}. 1286 1287 \end{description} 1337 and a 2D field of neutral drag coefficient. 1338 Then using the routine TURB\_CORE\_1Z or TURB\_CORE\_2Z, and starting from the neutral drag coefficent provided, 1339 the drag coefficient is computed according to stable/unstable conditions of the air-sea interface following \citet{Large_Yeager_Rep04}. 1340 1288 1341 1289 1342 % Griffies doc: 1290 % When running ocean-ice simulations, we are not explicitly representing land processes, such as rivers, catchment areas, snow accumulation, etc. However, to reduce model drift, it is important to balance the hydrological cycle in ocean-ice models. We thus need to prescribe some form of global normalization to the precipitation minus evaporation plus river runoff. The result of the normalization should be a global integrated zero net water input to the ocean-ice system over a chosen time scale. 1291 %How often the normalization is done is a matter of choice. In mom4p1, we choose to do so at each model time step, so that there is always a zero net input of water to the ocean-ice system. Others choose to normalize over an annual cycle, in which case the net imbalance over an annual cycle is used to alter the subsequent year�s water budget in an attempt to damp the annual water imbalance. Note that the annual budget approach may be inappropriate with interannually varying precipitation forcing. 1292 %When running ocean-ice coupled models, it is incorrect to include the water transport between the ocean and ice models when aiming to balance the hydrological cycle. The reason is that it is the sum of the water in the ocean plus ice that should be balanced when running ocean-ice models, not the water in any one sub-component. As an extreme example to illustrate the issue, consider an ocean-ice model with zero initial sea ice. As the ocean-ice model spins up, there should be a net accumulation of water in the growing sea ice, and thus a net loss of water from the ocean. The total water contained in the ocean plus ice system is constant, but there is an exchange of water between the subcomponents. This exchange should not be part of the normalization used to balance the hydrological cycle in ocean-ice models. 1293 1294 1343 % When running ocean-ice simulations, we are not explicitly representing land processes, 1344 % such as rivers, catchment areas, snow accumulation, etc. However, to reduce model drift, 1345 % it is important to balance the hydrological cycle in ocean-ice models. 1346 % We thus need to prescribe some form of global normalization to the precipitation minus evaporation plus river runoff. 1347 % The result of the normalization should be a global integrated zero net water input to the ocean-ice system over 1348 % a chosen time scale. 1349 %How often the normalization is done is a matter of choice. In mom4p1, we choose to do so at each model time step, 1350 % so that there is always a zero net input of water to the ocean-ice system. 1351 % Others choose to normalize over an annual cycle, in which case the net imbalance over an annual cycle is used 1352 % to alter the subsequent year�s water budget in an attempt to damp the annual water imbalance. 1353 % Note that the annual budget approach may be inappropriate with interannually varying precipitation forcing. 1354 % When running ocean-ice coupled models, it is incorrect to include the water transport between the ocean 1355 % and ice models when aiming to balance the hydrological cycle. 1356 % The reason is that it is the sum of the water in the ocean plus ice that should be balanced when running ocean-ice models, 1357 % not the water in any one sub-component. As an extreme example to illustrate the issue, 1358 % consider an ocean-ice model with zero initial sea ice. As the ocean-ice model spins up, 1359 % there should be a net accumulation of water in the growing sea ice, and thus a net loss of water from the ocean. 1360 % The total water contained in the ocean plus ice system is constant, but there is an exchange of water between 1361 % the subcomponents. This exchange should not be part of the normalization used to balance the hydrological cycle 1362 % in ocean-ice models. 1363 1364 1365 \end{document}
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