Changeset 14789 for NEMO/branches/2021/dev_r13747_HPC-11_mcastril_HPDAonline_DiagGPU/doc/latex/NEMO/subfiles/chap_SBC.tex
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NEMO/branches/2021/dev_r13747_HPC-11_mcastril_HPDAonline_DiagGPU/doc/latex/NEMO/subfiles/chap_SBC.tex
r13165 r14789 1 1 \documentclass[../main/NEMO_manual]{subfiles} 2 \usepackage{fontspec}3 \usepackage{fontawesome}4 2 5 3 \begin{document} 6 4 7 \chapter{Surface Boundary Condition (SBC, SAS, ISF, ICB )}5 \chapter{Surface Boundary Condition (SBC, SAS, ISF, ICB, TDE)} 8 6 \label{chap:SBC} 9 10 \thispagestyle{plain}11 7 12 8 \chaptertoc … … 18 14 Release & Author(s) & Modifications \\ 19 15 \hline 16 {\em next} & {\em Simon M{\" u}ller} & {\em Update of \autoref{sec:SBC_TDE}; revision of \autoref{subsec:SBC_fwb}}\\[2mm] 17 {\em next} & {\em Pierre Mathiot} & {\em update of the ice shelf section (2019 developments)}\\[2mm] 20 18 {\em 4.0} & {\em ...} & {\em ...} \\ 21 19 {\em 3.6} & {\em ...} & {\em ...} \\ … … 75 73 (\np[=0..3]{nn_ice}{nn\_ice}), 76 74 \item the addition of river runoffs as surface freshwater fluxes or lateral inflow (\np[=.true.]{ln_rnf}{ln\_rnf}), 77 \item the addition of ice-shelf melting as lateral inflow (parameterisation) or78 as fluxes applied at the land-ice ocean interface (\np[=.true.]{ln_isf}{ln\_isf}),79 75 \item the addition of a freshwater flux adjustment in order to avoid a mean sea-level drift 80 76 (\np[=0..2]{nn_fwb}{nn\_fwb}), … … 100 96 One of these is modification by icebergs (see \autoref{sec:SBC_ICB_icebergs}), 101 97 which act as drifting sources of fresh water. 102 Another example of modification is that due to the ice shelf melting/freezing (see \autoref{sec:SBC_isf}),103 which provides additional sources of fresh water.104 98 105 99 %% ================================================================================================= … … 525 519 See \autoref{subsec:SBC_ssr} for its specification. 526 520 527 528 529 530 531 532 533 %% ================================================================================================= 534 \pagebreak 535 \newpage 521 %% ================================================================================================= 536 522 \section[Bulk formulation (\textit{sbcblk.F90})]{Bulk formulation (\protect\mdl{sbcblk})} 537 523 \label{sec:SBC_blk} … … 557 543 558 544 Note: all the NEMO Fortran routines involved in the present section have been 559 560 the \href{https://brodeau.github.io/aerobulk/}{\texttt{AeroBulk}} open-source project561 \citep{brodeau.barnier.ea_JPO1 7}.545 initially developed (and are still developed in parallel) in 546 the \href{https://brodeau.github.io/aerobulk}{\texttt{AeroBulk}} open-source project 547 \citep{brodeau.barnier.ea_JPO16}. 562 548 563 549 %%% Bulk formulae are this: 564 \subsection{Bulk formulae}\label{subsec:SBC_blkform} 565 % 550 \subsection{Bulk formulae} 551 \label{subsec:SBC_blkform} 552 566 553 In NEMO, the set of equations that relate each component of the surface fluxes 567 554 to the near-surface atmosphere and sea surface states writes 568 % 569 \begin{subequations}\label{eq_bulk} 555 556 \begin{subequations} 557 \label{eq:SBC_bulk} 570 558 \label{eq:SBC_bulk_form} 571 \begin{eqnarray} 572 \mathbf{\tau} &=& \rho~ C_D ~ \mathbf{U}_z ~ U_B \\ 573 Q_H &=& \rho~C_H~C_P~\big[ \theta_z - T_s \big] ~ U_B \\ 574 E &=& \rho~C_E ~\big[ q_s - q_z \big] ~ U_B \\ 575 Q_L &=& -L_v \, E \\ 576 % 577 Q_{sr} &=& (1 - a) Q_{sw\downarrow} \\ 578 Q_{ir} &=& \delta (Q_{lw\downarrow} -\sigma T_s^4) 579 \end{eqnarray} 559 \begin{align} 560 \mathbf{\tau} &= \rho~ C_D ~ \mathbf{U}_z ~ U_B \\ 561 Q_H &= \rho~C_H~C_P~\big[ \theta_z - T_s \big] ~ U_B \\ 562 E &= \rho~C_E ~\big[ q_s - q_z \big] ~ U_B \\ 563 Q_L &= -L_v \, E \\ 564 Q_{sr} &= (1 - a) Q_{sw\downarrow} \\ 565 Q_{ir} &= \delta (Q_{lw\downarrow} -\sigma T_s^4) 566 \end{align} 580 567 \end{subequations} 581 % 568 582 569 with 583 570 \[ \theta_z \simeq T_z+\gamma z \] 584 571 \[ q_s \simeq 0.98\,q_{sat}(T_s,p_a ) \] 585 %586 572 from which, the the non-solar heat flux is \[ Q_{ns} = Q_L + Q_H + Q_{ir} \] 587 %588 573 where $\mathbf{\tau}$ is the wind stress vector, $Q_H$ the sensible heat flux, 589 574 $E$ the evaporation, $Q_L$ the latent heat flux, and $Q_{ir}$ the net longwave 590 575 flux. 591 %592 576 $Q_{sw\downarrow}$ and $Q_{lw\downarrow}$ are the surface downwelling shortwave 593 577 and longwave radiative fluxes, respectively. 594 %595 578 Note: a positive sign for $\mathbf{\tau}$, $Q_H$, $Q_L$, $Q_{sr}$ or $Q_{ir}$ 596 579 implies a gain of the relevant quantity for the ocean, while a positive $E$ 597 580 implies a freshwater loss for the ocean. 598 %599 581 $\rho$ is the density of air. $C_D$, $C_H$ and $C_E$ are the bulk transfer 600 582 coefficients for momentum, sensible heat, and moisture, respectively. 601 %602 583 $C_P$ is the heat capacity of moist air, and $L_v$ is the latent heat of 603 584 vaporization of water. 604 %605 585 $\theta_z$, $T_z$ and $q_z$ are the potential temperature, absolute temperature, 606 586 and specific humidity of air at height $z$ above the sea surface, 607 587 respectively. $\gamma z$ is a temperature correction term which accounts for the 608 588 adiabatic lapse rate and approximates the potential temperature at height 609 $z$ \citep{josey.gulev.ea_2013}. 610 % 589 $z$ \citep{josey.gulev.ea_OCC13}. 611 590 $\mathbf{U}_z$ is the wind speed vector at height $z$ above the sea surface 612 (possibly referenced to the surface current $\mathbf{u_0}$, 613 section \ref{s_res1}.\ref{ss_current}). 614 % 591 (possibly referenced to the surface current $\mathbf{u_0}$).%, 592 %\autoref{s_res1}.\autoref{ss_current}). %% Undefined references 615 593 The bulk scalar wind speed, namely $U_B$, is the scalar wind speed, 616 594 $|\mathbf{U}_z|$, with the potential inclusion of a gustiness contribution. 617 %618 595 $a$ and $\delta$ are the albedo and emissivity of the sea surface, respectively.\\ 619 %620 596 %$p_a$ is the mean sea-level pressure (SLP). 621 %622 597 $T_s$ is the sea surface temperature. $q_s$ is the saturation specific humidity 623 598 of air at temperature $T_s$; it includes a 2\% reduction to account for the 624 presence of salt in seawater \citep{sverdrup.johnson.ea_ 1942,kraus.businger_QJRMS96}.599 presence of salt in seawater \citep{sverdrup.johnson.ea_bk42,kraus.businger_QJRMS96}. 625 600 Depending on the bulk parametrization used, $T_s$ can either be the temperature 626 601 at the air-sea interface (skin temperature, hereafter SSST) or at typically a 627 602 few tens of centimeters below the surface (bulk sea surface temperature, 628 603 hereafter SST). 629 %630 604 The SSST differs from the SST due to the contributions of two effects of 631 605 opposite sign, the \emph{cool skin} and \emph{warm layer} (hereafter CS and WL, 632 respectively, see section\,\ref{subsec:SBC_skin}). 633 % 606 respectively, see \autoref{subsec:SBC_skin}). 634 607 Technically, when the ECMWF or COARE* bulk parametrizations are selected 635 608 (\np[=.true.]{ln_ECMWF}{ln\_ECMWF} or \np[=.true.]{ln_COARE*}{ln\_COARE\*}), … … 639 612 640 613 For more details on all these aspects the reader is invited to refer 641 to \citet{brodeau.barnier.ea_JPO17}. 642 643 644 645 \subsection{Bulk parametrizations}\label{subsec:SBC_blk_ocean} 614 to \citet{brodeau.barnier.ea_JPO16}. 615 616 \subsection{Bulk parametrizations} 617 \label{subsec:SBC_blk_ocean} 646 618 %%%\label{subsec:SBC_param} 647 619 … … 653 625 height (from \np{rn_zqt}{rn\_zqt} to \np{rn_zu}{rn\_zu}). 654 626 655 656 657 627 For the open ocean, four bulk parametrization algorithms are available in NEMO: 628 658 629 \begin{itemize} 659 \item NCAR, formerly known as CORE, \citep{large.yeager_ rpt04,large.yeager_CD09}630 \item NCAR, formerly known as CORE, \citep{large.yeager_trpt04,large.yeager_CD09} 660 631 \item COARE 3.0 \citep{fairall.bradley.ea_JC03} 661 632 \item COARE 3.6 \citep{edson.jampana.ea_JPO13} … … 663 634 \end{itemize} 664 635 665 666 636 With respect to version 3, the principal advances in version 3.6 of the COARE 667 637 bulk parametrization are built around improvements in the representation of the 668 638 effects of waves on 669 fluxes \citep{edson.jampana.ea_JPO13,brodeau.barnier.ea_JPO1 7}. This includes639 fluxes \citep{edson.jampana.ea_JPO13,brodeau.barnier.ea_JPO16}. This includes 670 640 improved relationships of surface roughness, and whitecap fraction on wave 671 641 parameters. It is therefore recommended to chose version 3.6 over 3. 672 642 673 674 675 676 \subsection{Cool-skin and warm-layer parametrizations}\label{subsec:SBC_skin} 677 %\subsection[Cool-skin and warm-layer parameterizations 678 %(\forcode{ln_skin_cs} \& \forcode{ln_skin_wl})]{Cool-skin and warm-layer parameterizations (\protect\np{ln_skin_cs}{ln\_skin\_cs} \& \np{ln_skin_wl}{ln\_skin\_wl})} 679 %\label{subsec:SBC_skin} 680 % 643 \subsection[Cool-skin and warm-layer parameterizations ( \forcode{ln_skin_cs} \& \forcode{ln_skin_wl} )] 644 {Cool-skin and warm-layer parameterizations (\protect\np{ln_skin_cs}{ln\_skin\_cs} \& \np{ln_skin_wl}{ln\_skin\_wl})} 645 \label{subsec:SBC_skin} 646 681 647 As opposed to the NCAR bulk parametrization, more advanced bulk 682 648 parametrizations such as COARE3.x and ECMWF are meant to be used with the skin 683 649 temperature $T_s$ rather than the bulk SST (which, in NEMO is the temperature at 684 the first T-point level, see section\,\ref{subsec:SBC_blkform}).685 % 650 the first T-point level, see \autoref{subsec:SBC_blkform}). 651 686 652 As such, the relevant cool-skin and warm-layer parametrization must be 687 653 activated through \np[=T]{ln_skin_cs}{ln\_skin\_cs} … … 692 658 693 659 For the cool-skin scheme parametrization COARE and ECMWF algorithms share the same 694 basis: \citet{fairall.bradley.ea_JGR 96}. With some minor updates based695 on \citet{zeng.beljaars_GRL05} for ECMWF , and \citet{fairall.ea_19} for COARE660 basis: \citet{fairall.bradley.ea_JGRO96}. With some minor updates based 661 on \citet{zeng.beljaars_GRL05} for ECMWF \iffalse, and \citet{fairall.ea_19?} for COARE \fi 696 662 3.6. 697 663 … … 700 666 turbulence input from Langmuir circulation). 701 667 702 Importantly, COARE warm-layer scheme \ citep{fairall.ea_19}includes a prognostic668 Importantly, COARE warm-layer scheme \iffalse \citep{fairall.ea_19?} \fi includes a prognostic 703 669 equation for the thickness of the warm-layer, while it is considered as constant 704 670 in the ECWMF algorithm. 705 706 671 707 672 \subsection{Appropriate use of each bulk parametrization} … … 713 678 temperature is the bulk SST. Hence the following namelist parameters must be 714 679 set: 715 % 716 \begin{ verbatim}680 681 \begin{forlines} 717 682 ... 718 683 ln_NCAR = .true. … … 725 690 ... 726 691 ln_humi_sph = .true. ! humidity "sn_humi" is specific humidity [kg/kg] 727 \end{verbatim} 728 692 \end{forlines} 729 693 730 694 \subsubsection{ECMWF} 731 % 695 732 696 With an atmospheric forcing based on a reanalysis of the ECMWF, such as the 733 697 Drakkar Forcing Set \citep{brodeau.barnier.ea_OM10}, we strongly recommend to … … 736 700 humidity are provided at the 2\,m height, and given that the humidity is 737 701 distributed as the dew-point temperature, the namelist must be tuned as follows: 738 % 739 \begin{ verbatim}702 703 \begin{forlines} 740 704 ... 741 705 ln_ECMWF = .true. … … 749 713 ln_humi_dpt = .true. ! humidity "sn_humi" is dew-point temperature [K] 750 714 ... 751 \end{ verbatim}752 % 715 \end{forlines} 716 753 717 Note: when \np{ln_ECMWF}{ln\_ECMWF} is selected, the selection 754 718 of \np{ln_skin_cs}{ln\_skin\_cs} and \np{ln_skin_wl}{ln\_skin\_wl} implicitly … … 756 720 respectively (found in \textit{sbcblk\_skin\_ecmwf.F90}). 757 721 758 759 722 \subsubsection{COARE 3.x} 760 % 723 761 724 Since the ECMWF parametrization is largely based on the COARE* parametrization, 762 725 the two algorithms are very similar in terms of structure and closure 763 726 approach. As such, the namelist tuning for COARE 3.x is identical to that of 764 727 ECMWF: 765 % 766 \begin{ verbatim}728 729 \begin{forlines} 767 730 ... 768 731 ln_COARE3p6 = .true. … … 771 734 ln_skin_wl = .true. ! use the warm-layer parameterization 772 735 ... 773 \end{ verbatim}736 \end{forlines} 774 737 775 738 Note: when \np[=T]{ln_COARE3p0}{ln\_COARE3p0} is selected, the selection … … 778 741 respectively (found in \textit{sbcblk\_skin\_coare.F90}). 779 742 780 781 743 %lulu 782 783 784 744 785 745 % In a typical bulk algorithm, the BTCs under neutral stability conditions are … … 791 751 % and $q_z$. 792 752 793 794 795 753 \subsection{Prescribed near-surface atmospheric state} 796 754 … … 799 757 different bulk formulae are used for the turbulent fluxes computation over the 800 758 ocean and over sea-ice surface. 801 %802 759 803 760 %The choice is made by setting to true one of the following namelist … … 861 818 the namsbc\_blk namelist (see \autoref{subsec:SBC_fldread}). 862 819 863 864 820 \subsubsection{Air humidity} 865 821 … … 867 823 [kg/kg], relative humidity [\%], or dew-point temperature [K] (LINK to namelist 868 824 parameters)... 869 870 871 ~\\872 873 874 875 876 877 878 879 880 881 825 882 826 %% ================================================================================================= … … 888 832 %their neutral transfer coefficients relationships with neutral wind. 889 833 %\begin{itemize} 890 %\item NCAR (\np[=.true.]{ln_NCAR}{ln\_NCAR}): The NCAR bulk formulae have been developed by \citet{large.yeager_ rpt04}.834 %\item NCAR (\np[=.true.]{ln_NCAR}{ln\_NCAR}): The NCAR bulk formulae have been developed by \citet{large.yeager_trpt04}. 891 835 % They have been designed to handle the NCAR forcing, a mixture of NCEP reanalysis and satellite data. 892 836 % They use an inertial dissipative method to compute the turbulent transfer coefficients 893 837 % (momentum, sensible heat and evaporation) from the 10m wind speed, air temperature and specific humidity. 894 % This \citet{large.yeager_ rpt04} dataset is available through838 % This \citet{large.yeager_trpt04} dataset is available through 895 839 % the \href{http://nomads.gfdl.noaa.gov/nomads/forms/mom4/NCAR.html}{GFDL web site}. 896 840 % Note that substituting ERA40 to NCEP reanalysis fields does not require changes in the bulk formulea themself. … … 907 851 \label{subsec:SBC_blk_ice} 908 852 909 910 853 \texttt{\#out\_of\_place:} 911 854 For sea-ice, three possibilities can be selected: 912 855 a constant transfer coefficient (1.4e-3; default 913 value), \citet{lupkes.gryanik.ea_JGR 12} (\np{ln_Cd_L12}{ln\_Cd\_L12}),856 value), \citet{lupkes.gryanik.ea_JGRA12} (\np{ln_Cd_L12}{ln\_Cd\_L12}), 914 857 and \citet{lupkes.gryanik_JGR15} (\np{ln_Cd_L15}{ln\_Cd\_L15}) parameterizations 915 858 \texttt{\#out\_of\_place.} 916 859 917 918 919 920 860 Surface turbulent fluxes between sea-ice and the atmosphere can be computed in three different ways: 921 861 922 862 \begin{itemize} 923 \item Constant value (\ np[ Cd_ice=1.4e-3 ]{constant value}{constant\ value}):863 \item Constant value (\forcode{Cd_ice=1.4e-3}): 924 864 default constant value used for momentum and heat neutral transfer coefficients 925 \item \citet{lupkes.gryanik.ea_JGR 12} (\np[=.true.]{ln_Cd_L12}{ln\_Cd\_L12}):865 \item \citet{lupkes.gryanik.ea_JGRA12} (\np[=.true.]{ln_Cd_L12}{ln\_Cd\_L12}): 926 866 This scheme adds a dependency on edges at leads, melt ponds and flows 927 867 of the constant neutral air-ice drag. After some approximations, … … 1013 953 1014 954 %% ================================================================================================= 1015 \section [Surface tides (\textit{sbctide.F90})]{Surface tides (\protect\mdl{sbctide})}1016 \label{sec:SBC_ tide}955 \section{Surface tides (TDE)} 956 \label{sec:SBC_TDE} 1017 957 1018 958 \begin{listing} … … 1022 962 \end{listing} 1023 963 1024 The tidal forcing, generated by the gravity forces of the Earth-Moon and Earth-Sun sytems, 1025 is activated if \np{ln_tide}{ln\_tide} and \np{ln_tide_pot}{ln\_tide\_pot} are both set to \forcode{.true.} in \nam{_tide}{\_tide}. 1026 This translates as an additional barotropic force in the momentum \autoref{eq:MB_PE_dyn} such that: 964 \subsection{Tidal constituents} 965 Ocean model component TDE provides the common functionality for tidal forcing 966 and tidal analysis in the model framework. This includes the computation of the gravitational 967 surface forcing, as well as support for lateral forcing at open boundaries (see 968 \autoref{subsec:LBC_bdy_tides}) and tidal harmonic analysis \iffalse (see 969 \autoref{subsec:DIA_diamlr?} and \autoref{subsec:DIA_diadetide?}) \fi . The module is 970 activated with \np[=.true.]{ln_tide}{ln\_tide} in namelist 971 \nam{_tide}{\_tide}. It provides the same 34 tidal constituents that are 972 included in the 973 \href{https://www.aviso.altimetry.fr/en/data/products/auxiliary-products/global-tide-fes.html}{FES2014 974 ocean tide model}: Mf, Mm, Ssa, Mtm, Msf, Msqm, Sa, K1, O1, P1, Q1, J1, S1, 975 M2, S2, N2, K2, nu2, mu2, 2N2, L2, T2, eps2, lam2, R2, M3, MKS2, MN4, MS4, M4, 976 N4, S4, M6, and M8; see file \textit{tide.h90} and \mdl{tide\_mod} for further 977 information and references\footnote{As a legacy option \np{ln_tide_var}{ln\_tide\_var} can be 978 set to \forcode{0}, in which case the 19 tidal constituents (M2, N2, 2N2, S2, 979 K2, K1, O1, Q1, P1, M4, Mf, Mm, Msqm, Mtm, S1, MU2, NU2, L2, and T2; see file 980 \textit{tide.h90}) and associated parameters that have been available in NEMO version 981 4.0 and earlier are available}. Constituents to be included in the tidal forcing 982 (surface and lateral boundaries) are selected by enumerating their respective 983 names in namelist array \np{sn_tide_cnames}{sn\_tide\_cnames}.\par 984 985 \subsection{Surface tidal forcing} 986 Surface tidal forcing can be represented in the model through an additional 987 barotropic force in the momentum equation (\autoref{eq:MB_PE_dyn}) such that: 1027 988 \[ 1028 % \label{eq:SBC_PE_dyn_tides} 1029 \frac{\partial {\mathrm {\mathbf U}}_h }{\partial t}= ... 1030 +g\nabla (\Pi_{eq} + \Pi_{sal}) 989 \frac{\partial {\mathrm {\mathbf U}}_h }{\partial t} = \ldots +g\nabla (\gamma 990 \Pi_{eq} + \Pi_{sal}) 1031 991 \] 1032 where $\Pi_{eq}$ stands for the equilibrium tidal forcing and 1033 $\Pi_{sal}$ is a self-attraction and loading term (SAL). 1034 1035 The equilibrium tidal forcing is expressed as a sum over a subset of 1036 constituents chosen from the set of available tidal constituents 1037 defined in file \hf{SBC/tide} (this comprises the tidal 1038 constituents \textit{M2, N2, 2N2, S2, K2, K1, O1, Q1, P1, M4, Mf, Mm, 1039 Msqm, Mtm, S1, MU2, NU2, L2}, and \textit{T2}). Individual 1040 constituents are selected by including their names in the array 1041 \np{clname}{clname} in \nam{_tide}{\_tide} (e.g., \np{clname}{clname}\forcode{(1)='M2', } 1042 \np{clname}{clname}\forcode{(2)='S2'} to select solely the tidal consituents \textit{M2} 1043 and \textit{S2}). Optionally, when \np{ln_tide_ramp}{ln\_tide\_ramp} is set to 1044 \forcode{.true.}, the equilibrium tidal forcing can be ramped up 1045 linearly from zero during the initial \np{rdttideramp}{rdttideramp} days of the 1046 model run. 992 where $\gamma \Pi_{eq}$ stands for the equilibrium tidal forcing scaled by a spatially 993 uniform tilt factor $\gamma$, and $\Pi_{sal}$ is an optional 994 self-attraction and loading term (SAL). These additional terms are enabled when, 995 in addition to \np[=.true.]{ln_tide}{ln\_tide}), 996 \np[=.true.]{ln_tide_pot}{ln\_tide\_pot}.\par 997 998 The equilibrium tidal forcing is expressed as a sum over the subset of 999 constituents listed in \np{sn_tide_cnames}{sn\_tide\_cnames} of 1000 \nam{_tide} (e.g., 1001 \begin{forlines} 1002 sn_tide_cnames(1) = 'M2' 1003 sn_tide_cnames(2) = 'K1' 1004 sn_tide_cnames(3) = 'S2' 1005 sn_tide_cnames(4) = 'O1' 1006 \end{forlines} 1007 to select the four tidal constituents of strongest equilibrium tidal 1008 potential). The tidal tilt factor $\gamma = 1 + k - h$ includes the 1009 Love numbers $k$ and $h$ \citep{love_PRSL09}; this factor is 1010 configurable using \np{rn_tide_gamma}{rn\_tide\_gamma} (default value 0.7). Optionally, 1011 when \np[=.true.]{ln_tide_ramp}{ln\_tide\_ramp}, the equilibrium tidal 1012 forcing can be ramped up linearly from zero during the initial 1013 \np{rn_tide_ramp_dt}{rn\_tide\_ramp\_dt} days of the model run.\par 1047 1014 1048 1015 The SAL term should in principle be computed online as it depends on 1049 1016 the model tidal prediction itself (see \citet{arbic.garner.ea_DSR04} for a 1050 discussion about the practical implementation of this term). 1051 Nevertheless, the complex calculations involved would make this 1052 computationally too expensive. Here, two options are available: 1053 $\Pi_{sal}$ generated by an external model can be read in 1054 (\np[=.true.]{ln_read_load}{ln\_read\_load}), or a ``scalar approximation'' can be 1055 used (\np[=.true.]{ln_scal_load}{ln\_scal\_load}). In the latter case 1017 discussion about the practical implementation of this term). The complex 1018 calculations involved in such computations, however, are computationally very 1019 expensive. Here, two mutually exclusive simpler variants are available: 1020 amplitudes generated by an external model for oscillatory $\Pi_{sal}$ 1021 contributions from each of the selected tidal constituents can be read in 1022 (\np[=.true.]{ln_read_load}{ln\_read\_load}) from the file specified in 1023 \np{cn_tide_load}{cn\_tide\_load} (the variable names are comprised of the 1024 tidal-constituent name and suffixes \forcode{_z1} and \forcode{_z2} for the two 1025 orthogonal components, respectively); alternatively, a ``scalar approximation'' 1026 can be used (\np[=.true.]{ln_scal_load}{ln\_scal\_load}), where 1056 1027 \[ 1057 1028 \Pi_{sal} = \beta \eta, 1058 1029 \] 1059 where $\beta$ (\np{rn_scal_load}{rn\_scal\_load} with a default value of 0.094) is a 1060 spatially constant scalar, often chosen to minimize tidal prediction 1061 errors. Setting both \np{ln_read_load}{ln\_read\_load} and \np{ln_scal_load}{ln\_scal\_load} to 1062 \forcode{.false.} removes the SAL contribution. 1030 with a spatially uniform coefficient $\beta$, which can be configured 1031 via \np{rn_scal_load}{rn\_scal\_load} (default value 0.094) and is 1032 often tuned to minimize tidal prediction errors.\par 1033 1034 For diagnostic purposes, the forcing potential of the individual tidal 1035 constituents (incl. load ptential, if activated) and the total forcing 1036 potential (incl. load potential, if activated) can be made available 1037 as diagnostic output by setting 1038 \np[=.true.]{ln_tide_dia}{ln\_tide\_dia} (fields 1039 \forcode{tide_pot_<constituent>} and \forcode{tide_pot}).\par 1063 1040 1064 1041 %% ================================================================================================= … … 1201 1178 1202 1179 %% ================================================================================================= 1203 \section[Ice shelf melting (\textit{sbcisf.F90})]{Ice shelf melting (\protect\mdl{sbcisf})}1180 \section[Ice Shelf (ISF)]{Interaction with ice shelves (ISF)} 1204 1181 \label{sec:SBC_isf} 1205 1182 1206 1183 \begin{listing} 1207 \nlst{nam sbc_isf}1208 \caption{\forcode{&nam sbc_isf}}1209 \label{lst:nam sbc_isf}1184 \nlst{namisf} 1185 \caption{\forcode{&namisf}} 1186 \label{lst:namisf} 1210 1187 \end{listing} 1211 1188 1212 The namelist variable in \nam{sbc}{sbc}, \np{nn_isf}{nn\_isf}, controls the ice shelf representation. 1213 Description and result of sensitivity test to \np{nn_isf}{nn\_isf} are presented in \citet{mathiot.jenkins.ea_GMD17}. 1214 The different options are illustrated in \autoref{fig:SBC_isf}. 1215 1189 The namelist variable in \nam{isf}{isf}, \np{ln_isf}{ln\_isf}, controls the ice shelf interactions: 1216 1190 \begin{description} 1217 \item [{\np[=1]{nn_isf}{nn\_isf}}]: The ice shelf cavity is represented (\np[=.true.]{ln_isfcav}{ln\_isfcav} needed). 1218 The fwf and heat flux are depending of the local water properties. 1219 1220 Two different bulk formulae are available: 1191 \item $\bullet$ representation of the ice shelf/ocean melting/freezing for opened cavity (cav, \np{ln_isfcav_mlt}{ln\_isfcav\_mlt}). 1192 \item $\bullet$ parametrisation of the ice shelf/ocean melting/freezing for closed cavities (par, \np{ln_isfpar_mlt}{ln\_isfpar\_mlt}). 1193 \item $\bullet$ coupling with an ice sheet model (\np{ln_isfcpl}{ln\_isfcpl}). 1194 \end{description} 1195 1196 \subsection{Ocean/Ice shelf fluxes in opened cavities} 1197 1198 \np{ln_isfcav_mlt}{ln\_isfcav\_mlt}\forcode{ = .true.} activates the ocean/ice shelf thermodynamics interactions at the ice shelf/ocean interface. 1199 If \np{ln_isfcav_mlt}{ln\_isfcav\_mlt}\forcode{ = .false.}, thermodynamics interactions are desctivated but the ocean dynamics inside the cavity is still active. 1200 The logical flag \np{ln_isfcav}{ln\_isfcav} control whether or not the ice shelf cavities are closed. \np{ln_isfcav}{ln\_isfcav} is not defined in the namelist but in the domcfg.nc input file.\\ 1201 1202 3 options are available to represent to ice-shelf/ocean fluxes at the interface: 1203 \begin{description} 1204 \item[\np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = 'spe'}]: 1205 The fresh water flux is specified by a forcing fields \np{sn_isfcav_fwf}{sn\_isfcav\_fwf}. Convention of the input file is: positive toward the ocean (i.e. positive for melting and negative for freezing). 1206 The latent heat fluxes is derived from the fresh water flux. 1207 The heat content flux is derived from the fwf flux assuming a temperature set to the freezing point in the top boundary layer (\np{rn_htbl}{rn\_htbl}) 1208 1209 \item[\np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = 'oasis'}]: 1210 The \forcode{'oasis'} is a prototype of what could be a method to spread precipitation on Antarctic ice sheet as ice shelf melt inside the cavity when a coupled model Atmosphere/Ocean is used. 1211 It has not been tested and therefore the model will stop if you try to use it. 1212 Actions will be undertake in 2020 to build a comprehensive interface to do so for Greenland, Antarctic and ice shelf (cav), ice shelf (par), icebergs, subglacial runoff and runoff. 1213 1214 \item[\np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = '2eq'}]: 1215 The heat flux and the fresh water flux (negative for melting) resulting from ice shelf melting/freezing are parameterized following \citet{Grosfeld1997}. 1216 This formulation is based on a balance between the vertical diffusive heat flux across the ocean top boundary layer (\autoref{eq:ISOMIP1}) 1217 and the latent heat due to melting/freezing (\autoref{eq:ISOMIP2}): 1218 1219 \begin{equation} 1220 \label{eq:ISOMIP1} 1221 \mathcal{Q}_h = \rho c_p \gamma (T_w - T_f) 1222 \end{equation} 1223 \begin{equation} 1224 \label{eq:ISOMIP2} 1225 q = \frac{-\mathcal{Q}_h}{L_f} 1226 \end{equation} 1227 1228 where $\mathcal{Q}_h$($W.m^{-2}$) is the heat flux,q($kg.s^{-1}m^{-2}$) the fresh-water flux, 1229 $L_f$ the specific latent heat, $T_w$ the temperature averaged over a boundary layer below the ice shelf (explained below), 1230 $T_f$ the freezing point using the pressure at the ice shelf base and the salinity of the water in the boundary layer, 1231 and $\gamma$ the thermal exchange coefficient. 1232 1233 \item[\np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = '3eq'}]: 1234 For realistic studies, the heat and freshwater fluxes are parameterized following \citep{Jenkins2001}. This formulation is based on three equations: 1235 a balance between the vertical diffusive heat flux across the boundary layer 1236 , the latent heat due to melting/freezing of ice and the vertical diffusive heat flux into the ice shelf (\autoref{eq:3eq1}); 1237 a balance between the vertical diffusive salt flux across the boundary layer and the salt source or sink represented by the melting/freezing (\autoref{eq:3eq2}); 1238 and a linear equation for the freezing temperature of sea water (\autoref{eq:3eq3}, detailed of the linearisation coefficient in \citet{AsayDavis2016}): 1239 1240 \begin{equation} 1241 \label{eq:3eq1} 1242 c_p \rho \gamma_T (T_w-T_b) = -L_f q - \rho_i c_{p,i} \kappa \frac{T_s - T_b}{h_{isf}} 1243 \end{equation} 1244 \begin{equation} 1245 \label{eq:3eq2} 1246 \rho \gamma_S (S_w - S_b) = (S_i - S_b)q 1247 \end{equation} 1248 \begin{equation} 1249 \label{eq:3eq3} 1250 T_b = \lambda_1 S_b + \lambda_2 +\lambda_3 z_{isf} 1251 \end{equation} 1252 1253 where $T_b$ is the temperature at the interface, $S_b$ the salinity at the interface, $\gamma_T$ and $\gamma_S$ the exchange coefficients for temperature and salt, respectively, 1254 $S_i$ the salinity of the ice (assumed to be 0), $h_{isf}$ the ice shelf thickness, $z_{isf}$ the ice shelf draft, $\rho_i$ the density of the iceshelf, 1255 $c_{p,i}$ the specific heat capacity of the ice, $\kappa$ the thermal diffusivity of the ice 1256 and $T_s$ the atmospheric surface temperature (at the ice/air interface, assumed to be -20C). 1257 The Liquidus slope ($\lambda_1$), the liquidus intercept ($\lambda_2$) and the Liquidus pressure coefficient ($\lambda_3$) 1258 for TEOS80 and TEOS10 are described in \citep{AsayDavis2016} and in \citep{Jourdain2017}. 1259 The linear system formed by \autoref{eq:3eq1}, \autoref{eq:3eq2} and the linearised equation for the freezing temperature of sea water (\autoref{eq:3eq3}) can be solved for $S_b$ or $T_b$. 1260 Afterward, the freshwater flux ($q$) and the heat flux ($\mathcal{Q}_h$) can be computed. 1261 1262 \end{description} 1263 1264 \begin{table}[h] 1265 \centering 1266 \caption{Description of the parameters hard coded into the ISF module} 1267 \label{tab:isf} 1268 \begin{tabular}{|l|l|l|l|} 1269 \hline 1270 Symbol & Description & Value & Unit \\ 1271 \hline 1272 $C_p$ & Ocean specific heat & 3992 & $J.kg^{-1}.K^{-1}$ \\ 1273 $L_f$ & Ice latent heat of fusion & $3.34 \times 10^5$ & $J.kg^{-1}$ \\ 1274 $C_{p,i}$ & Ice specific heat & 2000 & $J.kg^{-1}.K^{-1}$ \\ 1275 $\kappa$ & Heat diffusivity & $1.54 \times 10^{-6}$& $m^2.s^{-1}$ \\ 1276 $\rho_i$ & Ice density & 920 & $kg.m^3$ \\ 1277 \hline 1278 \end{tabular} 1279 \end{table} 1280 1281 Temperature and salinity used to compute the fluxes in \autoref{eq:ISOMIP1}, \autoref{eq:3eq1} and \autoref{eq:3eq2} are the average temperature in the top boundary layer \citep{losch_JGR08}. 1282 Its thickness is defined by \np{rn_htbl}{rn\_htbl}. 1283 The fluxes and friction velocity are computed using the mean temperature, salinity and velocity in the first \np{rn_htbl}{rn\_htbl} m. 1284 Then, the fluxes are spread over the same thickness (ie over one or several cells). 1285 If \np{rn_htbl}{rn\_htbl} is larger than top $e_{3}t$, there is no more direct feedback between the freezing point at the interface and the top cell temperature. 1286 This can lead to super-cool temperature in the top cell under melting condition. 1287 If \np{rn_htbl}{rn\_htbl} smaller than top $e_{3}t$, the top boundary layer thickness is set to the top cell thickness.\\ 1288 1289 Each melt formula (\np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = '3eq'} or \np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = '2eq'}) depends on an exchange coeficient ($\Gamma^{T,S}$) between the ocean and the ice. 1290 Below, the exchange coeficient $\Gamma^{T}$ and $\Gamma^{S}$ are respectively defined by \np{rn_gammat0}{rn\_gammat0} and \np{rn_gammas0}{rn\_gammas0}. 1291 There are 3 different ways to compute the exchange velocity: 1292 1293 \begin{description} 1294 \item[\np{cn_gammablk}{cn\_gammablk}\forcode{='spe'}]: 1295 The salt and heat exchange coefficients are constant and defined by: 1296 \[ 1297 \gamma^{T} = \Gamma^{T} 1298 \] 1299 \[ 1300 \gamma^{S} = \Gamma^{S} 1301 \] 1302 This is the recommended formulation for ISOMIP. 1303 1304 \item[\np{cn_gammablk}{cn\_gammablk}\forcode{='vel'}]: 1305 The salt and heat exchange coefficients are velocity dependent and defined as 1306 \[ 1307 \gamma^{T} = \Gamma^{T} \times u_{*} 1308 \] 1309 \[ 1310 \gamma^{S} = \Gamma^{S} \times u_{*} 1311 \] 1312 where $u_{*}$ is the friction velocity in the top boundary layer (ie first \np{rn_htbl}{rn\_htbl} meters). 1313 See \citet{jenkins.nicholls.ea_JPO10} for all the details on this formulation. It is the recommended formulation for realistic application and ISOMIP+/MISOMIP configuration. 1314 1315 \item[\np{cn_gammablk}{cn\_gammablk}\forcode{'vel\_stab'}]: 1316 The salt and heat exchange coefficients are velocity and stability dependent and defined as: 1317 \[ 1318 \gamma^{T,S} = \frac{u_{*}}{\Gamma_{Turb} + \Gamma^{T,S}_{Mole}} 1319 \] 1320 where $u_{*}$ is the friction velocity in the top boundary layer (ie first \np{rn_tbl}{rn\_htbl} meters), 1321 $\Gamma_{Turb}$ the contribution of the ocean stability and 1322 $\Gamma^{T,S}_{Mole}$ the contribution of the molecular diffusion. 1323 See \citet{holland.jenkins_JPO99} for all the details on this formulation. 1324 This formulation has not been extensively tested in NEMO (not recommended). 1325 \end{description} 1326 1327 \subsection{Ocean/Ice shelf fluxes in parametrised cavities} 1221 1328 1222 1329 \begin{description} 1223 \item [{\np[=1]{nn_isfblk}{nn\_isfblk}}]: The melt rate is based on a balance between the upward ocean heat flux and 1224 the latent heat flux at the ice shelf base. A complete description is available in \citet{hunter_rpt06}. 1225 \item [{\np[=2]{nn_isfblk}{nn\_isfblk}}]: The melt rate and the heat flux are based on a 3 equations formulation 1226 (a heat flux budget at the ice base, a salt flux budget at the ice base and a linearised freezing point temperature equation). 1227 A complete description is available in \citet{jenkins_JGR91}. 1330 1331 \item[\np{cn_isfpar_mlt}{cn\_isfpar\_mlt}\forcode{ = 'bg03'}]: 1332 The ice shelf cavities are not represented. 1333 The fwf and heat flux are computed using the \citet{beckmann.goosse_OM03} parameterisation of isf melting. 1334 The fluxes are distributed along the ice shelf edge between the depth of the average grounding line (GL) 1335 (\np{sn_isfpar_zmax}{sn\_isfpar\_zmax}) and the base of the ice shelf along the calving front 1336 (\np{sn_isfpar_zmin}{sn\_isfpar\_zmin}) as in (\np{cn_isfpar_mlt}{cn\_isfpar\_mlt}\forcode{ = 'spe'}). 1337 The effective melting length (\np{sn_isfpar_Leff}{sn\_isfpar\_Leff}) is read from a file. 1338 This parametrisation has not been tested since a while and based on \citet{Favier2019}, 1339 this parametrisation should probably not be used. 1340 1341 \item[\np{cn_isfpar_mlt}{cn\_isfpar\_mlt}\forcode{ = 'spe'}]: 1342 The ice shelf cavity is not represented. 1343 The fwf (\np{sn_isfpar_fwf}{sn\_isfpar\_fwf}) is prescribed and distributed along the ice shelf edge between 1344 the depth of the average grounding line (GL) (\np{sn_isfpar_zmax}{sn\_isfpar\_zmax}) and 1345 the base of the ice shelf along the calving front (\np{sn_isfpar_zmin}{sn\_isfpar\_min}). Convention of the input file is positive toward the ocean (i.e. positive for melting and negative for freezing). 1346 The heat flux ($Q_h$) is computed as $Q_h = fwf \times L_f$. 1347 1348 \item[\np{cn_isfpar_mlt}{cn\_isfpar\_mlt}\forcode{ = 'oasis'}]: 1349 The \forcode{'oasis'} is a prototype of what could be a method to spread precipitation on Antarctic ice sheet as ice shelf melt inside the cavity when a coupled model Atmosphere/Ocean is used. 1350 It has not been tested and therefore the model will stop if you try to use it. 1351 Action will be undertake in 2020 to build a comprehensive interface to do so for Greenland, Antarctic and ice shelf (cav), ice shelf (par), icebergs, subglacial runoff and runoff. 1352 1228 1353 \end{description} 1229 1354 1230 Temperature and salinity used to compute the melt are the average temperature in the top boundary layer \citet{losch_JGR08}. 1231 Its thickness is defined by \np{rn_hisf_tbl}{rn\_hisf\_tbl}. 1232 The fluxes and friction velocity are computed using the mean temperature, salinity and velocity in the the first \np{rn_hisf_tbl}{rn\_hisf\_tbl} m. 1233 Then, the fluxes are spread over the same thickness (ie over one or several cells). 1234 If \np{rn_hisf_tbl}{rn\_hisf\_tbl} larger than top $e_{3}t$, there is no more feedback between the freezing point at the interface and the the top cell temperature. 1235 This can lead to super-cool temperature in the top cell under melting condition. 1236 If \np{rn_hisf_tbl}{rn\_hisf\_tbl} smaller than top $e_{3}t$, the top boundary layer thickness is set to the top cell thickness.\\ 1237 1238 Each melt bulk formula depends on a exchange coeficient ($\Gamma^{T,S}$) between the ocean and the ice. 1239 There are 3 different ways to compute the exchange coeficient: 1240 \begin{description} 1241 \item [{\np[=0]{nn_gammablk}{nn\_gammablk}}]: The salt and heat exchange coefficients are constant and defined by \np{rn_gammas0}{rn\_gammas0} and \np{rn_gammat0}{rn\_gammat0}. 1242 \begin{gather*} 1243 % \label{eq:SBC_isf_gamma_iso} 1244 \gamma^{T} = rn\_gammat0 \\ 1245 \gamma^{S} = rn\_gammas0 1246 \end{gather*} 1247 This is the recommended formulation for ISOMIP. 1248 \item [{\np[=1]{nn_gammablk}{nn\_gammablk}}]: The salt and heat exchange coefficients are velocity dependent and defined as 1249 \begin{gather*} 1250 \gamma^{T} = rn\_gammat0 \times u_{*} \\ 1251 \gamma^{S} = rn\_gammas0 \times u_{*} 1252 \end{gather*} 1253 where $u_{*}$ is the friction velocity in the top boundary layer (ie first \np{rn_hisf_tbl}{rn\_hisf\_tbl} meters). 1254 See \citet{jenkins.nicholls.ea_JPO10} for all the details on this formulation. It is the recommended formulation for realistic application. 1255 \item [{\np[=2]{nn_gammablk}{nn\_gammablk}}]: The salt and heat exchange coefficients are velocity and stability dependent and defined as: 1256 \[ 1257 \gamma^{T,S} = \frac{u_{*}}{\Gamma_{Turb} + \Gamma^{T,S}_{Mole}} 1258 \] 1259 where $u_{*}$ is the friction velocity in the top boundary layer (ie first \np{rn_hisf_tbl}{rn\_hisf\_tbl} meters), 1260 $\Gamma_{Turb}$ the contribution of the ocean stability and 1261 $\Gamma^{T,S}_{Mole}$ the contribution of the molecular diffusion. 1262 See \citet{holland.jenkins_JPO99} for all the details on this formulation. 1263 This formulation has not been extensively tested in \NEMO\ (not recommended). 1264 \end{description} 1265 \item [{\np[=2]{nn_isf}{nn\_isf}}]: The ice shelf cavity is not represented. 1266 The fwf and heat flux are computed using the \citet{beckmann.goosse_OM03} parameterisation of isf melting. 1267 The fluxes are distributed along the ice shelf edge between the depth of the average grounding line (GL) 1268 (\np{sn_depmax_isf}{sn\_depmax\_isf}) and the base of the ice shelf along the calving front 1269 (\np{sn_depmin_isf}{sn\_depmin\_isf}) as in (\np[=3]{nn_isf}{nn\_isf}). 1270 The effective melting length (\np{sn_Leff_isf}{sn\_Leff\_isf}) is read from a file. 1271 \item [{\np[=3]{nn_isf}{nn\_isf}}]: The ice shelf cavity is not represented. 1272 The fwf (\np{sn_rnfisf}{sn\_rnfisf}) is prescribed and distributed along the ice shelf edge between 1273 the depth of the average grounding line (GL) (\np{sn_depmax_isf}{sn\_depmax\_isf}) and 1274 the base of the ice shelf along the calving front (\np{sn_depmin_isf}{sn\_depmin\_isf}). 1275 The heat flux ($Q_h$) is computed as $Q_h = fwf \times L_f$. 1276 \item [{\np[=4]{nn_isf}{nn\_isf}}]: The ice shelf cavity is opened (\np[=.true.]{ln_isfcav}{ln\_isfcav} needed). 1277 However, the fwf is not computed but specified from file \np{sn_fwfisf}{sn\_fwfisf}). 1278 The heat flux ($Q_h$) is computed as $Q_h = fwf \times L_f$. 1279 As in \np[=1]{nn_isf}{nn\_isf}, the fluxes are spread over the top boundary layer thickness (\np{rn_hisf_tbl}{rn\_hisf\_tbl}) 1280 \end{description} 1281 1282 $\bullet$ \np[=1]{nn_isf}{nn\_isf} and \np[=2]{nn_isf}{nn\_isf} compute a melt rate based on 1355 \np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = '2eq'}, \np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = '3eq'} and \np{cn_isfpar_mlt}{cn\_isfpar\_mlt}\forcode{ = 'bg03'} compute a melt rate based on 1283 1356 the water mass properties, ocean velocities and depth. 1284 Th is flux is thus highly dependent of the model resolution (horizontal and vertical),1285 realism of the water masses onto the shelf ...\\1286 1287 $\bullet$ \np[=3]{nn_isf}{nn\_isf} and \np[=4]{nn_isf}{nn\_isf} read the melt rate from a file.1357 The resulting fluxes are thus highly dependent of the model resolution (horizontal and vertical) and 1358 realism of the water masses onto the shelf.\\ 1359 1360 \np{cn_isfcav_mlt}{cn\_isfcav\_mlt}\forcode{ = 'spe'} and \np{cn_isfpar_mlt}{cn\_isfpar\_mlt}\forcode{ = 'spe'} read the melt rate from a file. 1288 1361 You have total control of the fwf forcing. 1289 1362 This can be useful if the water masses on the shelf are not realistic or 1290 1363 the resolution (horizontal/vertical) are too coarse to have realistic melting or 1291 for studies where you need to control your heat and fw input.\\ 1292 1293 The ice shelf melt is implemented as a volume flux as for the runoff. 1294 The fw addition due to the ice shelf melting is, at each relevant depth level, added to 1295 the horizontal divergence (\textit{hdivn}) in the subroutine \rou{sbc\_isf\_div}, called from \mdl{divhor}. 1364 for studies where you need to control your heat and fw input. 1365 However, if your forcing is not consistent with the dynamics below you can reach unrealistic low water temperature.\\ 1366 1367 The ice shelf fwf is implemented as a volume flux as for the runoff. 1368 The fwf addition due to the ice shelf melting is, at each relevant depth level, added to 1369 the horizontal divergence (\textit{hdivn}) in the subroutine \rou{isf\_hdiv}, called from \mdl{divhor}. 1296 1370 See the runoff section \autoref{sec:SBC_rnf} for all the details about the divergence correction.\\ 1371 1372 Description and result of sensitivity tests to \np{ln_isfcav_mlt}{ln\_isfcav\_mlt} and \np{ln_isfpar_mlt}{ln\_isfpar\_mlt} are presented in \citet{mathiot.jenkins.ea_GMD17}. 1373 The different options are illustrated in \autoref{fig:ISF}. 1297 1374 1298 1375 \begin{figure}[!t] 1299 1376 \centering 1300 \includegraphics[width=0.66\textwidth]{SBC_isf }1377 \includegraphics[width=0.66\textwidth]{SBC_isf_v4.2} 1301 1378 \caption[Ice shelf location and fresh water flux definition]{ 1302 1379 Illustration of the location where the fwf is injected and 1303 whether or not the fwf is interacti f or not depending of \protect\np{nn_isf}{nn\_isf}.}1304 \label{fig: SBC_isf}1380 whether or not the fwf is interactive or not.} 1381 \label{fig:ISF} 1305 1382 \end{figure} 1306 1383 1307 %% ================================================================================================= 1308 \section{Ice sheet coupling} 1309 \label{sec:SBC_iscpl} 1310 1311 \begin{listing} 1312 \nlst{namsbc_iscpl} 1313 \caption{\forcode{&namsbc_iscpl}} 1314 \label{lst:namsbc_iscpl} 1315 \end{listing} 1384 \subsection{Available outputs} 1385 The following outputs are availables via XIOS: 1386 \begin{description} 1387 \item[for parametrised cavities]: 1388 \begin{xmllines} 1389 <field id="isftfrz_par" long_name="freezing point temperature in the parametrization boundary layer" unit="degC" /> 1390 <field id="fwfisf_par" long_name="Ice shelf melt rate" unit="kg/m2/s" /> 1391 <field id="qoceisf_par" long_name="Ice shelf ocean heat flux" unit="W/m2" /> 1392 <field id="qlatisf_par" long_name="Ice shelf latent heat flux" unit="W/m2" /> 1393 <field id="qhcisf_par" long_name="Ice shelf heat content flux of injected water" unit="W/m2" /> 1394 <field id="fwfisf3d_par" long_name="Ice shelf melt rate" unit="kg/m2/s" grid_ref="grid_T_3D" /> 1395 <field id="qoceisf3d_par" long_name="Ice shelf ocean heat flux" unit="W/m2" grid_ref="grid_T_3D" /> 1396 <field id="qlatisf3d_par" long_name="Ice shelf latent heat flux" unit="W/m2" grid_ref="grid_T_3D" /> 1397 <field id="qhcisf3d_par" long_name="Ice shelf heat content flux of injected water" unit="W/m2" grid_ref="grid_T_3D" /> 1398 <field id="ttbl_par" long_name="temperature in the parametrisation boundary layer" unit="degC" /> 1399 <field id="isfthermald_par" long_name="thermal driving of ice shelf melting" unit="degC" /> 1400 \end{xmllines} 1401 \item[for open cavities]: 1402 \begin{xmllines} 1403 <field id="isftfrz_cav" long_name="freezing point temperature at ocean/isf interface" unit="degC" /> 1404 <field id="fwfisf_cav" long_name="Ice shelf melt rate" unit="kg/m2/s" /> 1405 <field id="qoceisf_cav" long_name="Ice shelf ocean heat flux" unit="W/m2" /> 1406 <field id="qlatisf_cav" long_name="Ice shelf latent heat flux" unit="W/m2" /> 1407 <field id="qhcisf_cav" long_name="Ice shelf heat content flux of injected water" unit="W/m2" /> 1408 <field id="fwfisf3d_cav" long_name="Ice shelf melt rate" unit="kg/m2/s" grid_ref="grid_T_3D" /> 1409 <field id="qoceisf3d_cav" long_name="Ice shelf ocean heat flux" unit="W/m2" grid_ref="grid_T_3D" /> 1410 <field id="qlatisf3d_cav" long_name="Ice shelf latent heat flux" unit="W/m2" grid_ref="grid_T_3D" /> 1411 <field id="qhcisf3d_cav" long_name="Ice shelf heat content flux of injected water" unit="W/m2" grid_ref="grid_T_3D" /> 1412 <field id="ttbl_cav" long_name="temperature in Losch tbl" unit="degC" /> 1413 <field id="isfthermald_cav" long_name="thermal driving of ice shelf melting" unit="degC" /> 1414 <field id="isfgammat" long_name="Ice shelf heat-transfert velocity" unit="m/s" /> 1415 <field id="isfgammas" long_name="Ice shelf salt-transfert velocity" unit="m/s" /> 1416 <field id="stbl" long_name="salinity in the Losh tbl" unit="1e-3" /> 1417 <field id="utbl" long_name="zonal current in the Losh tbl at T point" unit="m/s" /> 1418 <field id="vtbl" long_name="merid current in the Losh tbl at T point" unit="m/s" /> 1419 <field id="isfustar" long_name="ustar at T point used in ice shelf melting" unit="m/s" /> 1420 <field id="qconisf" long_name="Conductive heat flux through the ice shelf" unit="W/m2" /> 1421 \end{xmllines} 1422 \end{description} 1423 1424 %% ================================================================================================= 1425 \subsection{Ice sheet coupling} 1426 \label{subsec:ISF_iscpl} 1316 1427 1317 1428 Ice sheet/ocean coupling is done through file exchange at the restart step. 1318 At each restart step :1319 1320 \begin{ enumerate}1321 \item the ice sheet model send a new bathymetry and ice shelf draft netcdf file.1322 \item a new domcfg.nc file is built using the DOMAINcfg tools.1323 \item \NEMO\run for a specific period and output the average melt rate over the period.1324 \item the ice sheet model run using the melt rate outputed in step 4.1325 \item go back to 1.1326 \end{ enumerate}1327 1328 If \np [=.true.]{ln_iscpl}{ln\_iscpl}, the isf draft is assume to be different at each restart step with1429 At each restart step, the procedure is this one: 1430 1431 \begin{description} 1432 \item[Step 1]: the ice sheet model send a new bathymetry and ice shelf draft netcdf file. 1433 \item[Step 2]: a new domcfg.nc file is built using the DOMAINcfg tools. 1434 \item[Step 3]: NEMO run for a specific period and output the average melt rate over the period. 1435 \item[Step 4]: the ice sheet model run using the melt rate outputed in step 3. 1436 \item[Step 5]: go back to 1. 1437 \end{description} 1438 1439 If \np{ln_iscpl}{ln\_iscpl}\forcode{ = .true.}, the isf draft is assume to be different at each restart step with 1329 1440 potentially some new wet/dry cells due to the ice sheet dynamics/thermodynamics. 1330 The wetting and drying scheme applied on the restart is very simple and described below for the 6 different possible cases:1441 The wetting and drying scheme, applied on the restart, is very simple. The 6 different possible cases for the tracer and ssh are: 1331 1442 1332 1443 \begin{description} 1333 \item [Thin a cell down]: T/S/ssh are unchanged and U/V in the top cell are corrected to keep the barotropic transport (bt) constant 1334 ($bt_b=bt_n$). 1335 \item [Enlarge a cell]: See case "Thin a cell down" 1336 \item [Dry a cell]: mask, T/S, U/V and ssh are set to 0. 1337 Furthermore, U/V into the water column are modified to satisfy ($bt_b=bt_n$). 1338 \item [Wet a cell]: mask is set to 1, T/S is extrapolated from neighbours, $ssh_n = ssh_b$ and U/V set to 0. 1339 If no neighbours, T/S is extrapolated from old top cell value. 1340 If no neighbours along i,j and k (both previous test failed), T/S/U/V/ssh and mask are set to 0. 1341 \item [Dry a column]: mask, T/S, U/V are set to 0 everywhere in the column and ssh set to 0. 1342 \item [Wet a column]: set mask to 1, T/S is extrapolated from neighbours, ssh is extrapolated from neighbours and U/V set to 0. 1343 If no neighbour, T/S/U/V and mask set to 0. 1444 \item[Thin a cell]: 1445 T/S/ssh are unchanged. 1446 1447 \item[Enlarge a cell]: 1448 See case "Thin a cell down" 1449 1450 \item[Dry a cell]: 1451 Mask, T/S, U/V and ssh are set to 0. 1452 1453 \item[Wet a cell]: 1454 Mask is set to 1, T/S is extrapolated from neighbours, $ssh_n = ssh_b$. 1455 If no neighbours, T/S is extrapolated from old top cell value. 1456 If no neighbours along i,j and k (both previous tests failed), T/S/ssh and mask are set to 0. 1457 1458 \item[Dry a column]: 1459 mask, T/S and ssh are set to 0. 1460 1461 \item[Wet a column]: 1462 set mask to 1, T/S/ssh are extrapolated from neighbours. 1463 If no neighbour, T/S/ssh and mask set to 0. 1344 1464 \end{description} 1465 1466 The method described above will strongly affect the barotropic transport under an ice shelf when the geometry change. 1467 In order to keep the model stable, an adjustment of the dynamics at the initialisation after the coupling step is needed. 1468 The idea behind this is to keep $\pd[\eta]{t}$ as it should be without change in geometry at the initialisation. 1469 This will prevent any strong velocity due to large pressure gradient. 1470 To do so, we correct the horizontal divergence before $\pd[\eta]{t}$ is computed in the first time step.\\ 1345 1471 1346 1472 Furthermore, as the before and now fields are not compatible (modification of the geometry), … … 1349 1475 The horizontal extrapolation to fill new cell with realistic value is called \np{nn_drown}{nn\_drown} times. 1350 1476 It means that if the grounding line retreat by more than \np{nn_drown}{nn\_drown} cells between 2 coupling steps, 1351 the code will be unable to fill all the new wet cells properly .1477 the code will be unable to fill all the new wet cells properly and the model is likely to blow up at the initialisation. 1352 1478 The default number is set up for the MISOMIP idealised experiments. 1353 1479 This coupling procedure is able to take into account grounding line and calving front migration. 1354 However, it is a non-conservative proc esse.1480 However, it is a non-conservative proccess. 1355 1481 This could lead to a trend in heat/salt content and volume.\\ 1356 1482 1357 1483 In order to remove the trend and keep the conservation level as close to 0 as possible, 1358 a simple conservation scheme is available with \np[=.true.]{ln_hsb}{ln\_hsb}. 1359 The heat/salt/vol. gain/loss is diagnosed, as well as the location. 1360 A correction increment is computed and apply each time step during the next \np{rn_fiscpl}{rn\_fiscpl} time steps. 1361 For safety, it is advised to set \np{rn_fiscpl}{rn\_fiscpl} equal to the coupling period (smallest increment possible). 1362 The corrective increment is apply into the cell itself (if it is a wet cell), the neigbouring cells or the closest wet cell (if the cell is now dry). 1484 a simple conservation scheme is available with \np{ln_isfcpl_cons}{ln\_isfcpl\_cons}\forcode{ = .true.}. 1485 The heat/salt/vol. gain/loss are diagnosed, as well as the location. 1486 A correction increment is computed and applied each time step during the model run. 1487 The corrective increment are applied into the cells itself (if it is a wet cell), the neigbouring cells or the closest wet cell (if the cell is now dry). 1363 1488 1364 1489 %% ================================================================================================= … … 1409 1534 Melt water (and other variables on the configuration grid) are written into the main \NEMO\ model output files. 1410 1535 1536 By default, iceberg thermodynamic and dynamic are computed using ocean surface variable (sst, ssu, ssv) and the icebergs are not sensible to the bathymetry (only to land) whatever the iceberg draft. 1537 \citet{Merino_OM2016} developed an option to use vertical profiles of ocean currents and temperature instead (\np{ln_M2016}{ln\_M2016}). 1538 Full details on the sensitivity to this parameter in done in \citet{Merino_OM2016}. 1539 If \np{ln_M2016}{ln\_M2016} activated, \np{ln_icb_grd}{ln\_icb\_grd} activate (or not) an option to prevent thick icebergs to move across shallow bank (ie shallower than the iceberg draft). 1540 This option need to be used with care as it could required to either change the distribution to prevent generation of icebergs with draft larger than the bathymetry 1541 or to build a variable \forcode{maxclass} to prevent NEMO filling the icebergs classes too thick for the local bathymetry. 1542 1411 1543 Extensive diagnostics can be produced. 1412 1544 Separate output files are maintained for human-readable iceberg information. … … 1465 1597 Then using the routine \rou{sbcblk\_algo\_ncar} and starting from the neutral drag coefficent provided, 1466 1598 the drag coefficient is computed according to the stable/unstable conditions of the 1467 air-sea interface following \citet{large.yeager_ rpt04}.1599 air-sea interface following \citet{large.yeager_trpt04}. 1468 1600 1469 1601 %% ================================================================================================= … … 1576 1708 1577 1709 The surface stress felt by the ocean is the atmospheric stress minus the net stress going 1578 into the waves \citep{janssen.breivik.ea_ rpt13}. Therefore, when waves are growing, momentum and energy is spent and is not1710 into the waves \citep{janssen.breivik.ea_trpt13}. Therefore, when waves are growing, momentum and energy is spent and is not 1579 1711 available for forcing the mean circulation, while in the opposite case of a decaying sea 1580 1712 state, more momentum is available for forcing the ocean. … … 1795 1927 \label{subsec:SBC_fwb} 1796 1928 1797 For global ocean simulation, it can be useful to introduce a control of the mean sea level in order to 1798 prevent unrealistic drift of the sea surface height due to inaccuracy in the freshwater fluxes. 1799 In \NEMO, two way of controlling the freshwater budget are proposed: 1929 \begin{listing} 1930 \nlst{namsbc_fwb} 1931 \caption{\forcode{&namsbc_fwb}} 1932 \label{lst:namsbc_fwb} 1933 \end{listing} 1934 1935 For global ocean simulations, it can be useful to introduce a control of the 1936 mean sea level in order to prevent unrealistic drifting of the sea surface 1937 height due to unbalanced freshwater fluxes. In \NEMO, two options for 1938 controlling the freshwater budget are proposed. 1800 1939 1801 1940 \begin{description} 1802 \item [{\np[=0]{nn_fwb}{nn\_fwb}} ] no control at all.1803 The mean sea level isfree to drift, and will certainly do so.1804 \item [{\np[=1]{nn_fwb}{nn\_fwb}} ] global mean \textit{emp}set to zero at each model time step.1941 \item [{\np[=0]{nn_fwb}{nn\_fwb}}:] No control at all; the mean sea level is 1942 free to drift, and will certainly do so. 1943 \item [{\np[=1]{nn_fwb}{nn\_fwb}}:] The global mean \textit{emp} is set to zero at each model time step. 1805 1944 %GS: comment below still relevant ? 1806 1945 %Note that with a sea-ice model, this technique only controls the mean sea level with linear free surface and no mass flux between ocean and ice (as it is implemented in the current ice-ocean coupling). 1807 \item [{\np[=2]{nn_fwb}{nn\_fwb}}] freshwater budget is adjusted from the previous year annual mean budget which 1808 is read in the \textit{EMPave\_old.dat} file. 1809 As the model uses the Boussinesq approximation, the annual mean fresh water budget is simply evaluated from 1810 the change in the mean sea level at January the first and saved in the \textit{EMPav.dat} file. 1946 \item [{\np[=2]{nn_fwb}{nn\_fwb}}:] \textit{emp} is adjusted by adding a 1947 spatially uniform, annual-mean freshwater flux that balances the freshwater 1948 budget at the end of the previous year; as the model uses the Boussinesq 1949 approximation, the freshwater budget can be evaluated from the change in the 1950 mean sea level and in the ice and snow mass after the end of each simulation 1951 year; at the start of the model run, an initial adjustment flux can be set 1952 using parameter \np{rn_rwb0}{rn\_fwb0} in namelist \nam{sbc_fwb}{sbc\_fwb}. 1811 1953 \end{description} 1812 1954
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