Changeset 11954 for NEMO/branches/2019/dev_r11613_ENHANCE-04_namelists_as_internalfiles/doc/latex/NEMO/subfiles/chap_ZDF.tex
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NEMO/branches/2019/dev_r11613_ENHANCE-04_namelists_as_internalfiles/doc/latex/NEMO/subfiles/chap_ZDF.tex
r11599 r11954 28 28 \clearpage 29 29 30 %gm% Add here a small introduction to ZDF and naming of the different physics (similar to what have been written for TRA and DYN. 30 \cmtgm{ Add here a small introduction to ZDF and naming of the different physics 31 (similar to what have been written for TRA and DYN).} 31 32 32 33 %% ================================================================================================= … … 248 249 \begin{figure}[!t] 249 250 \centering 250 \includegraphics[width=0.66\textwidth]{ Fig_mixing_length}251 \includegraphics[width=0.66\textwidth]{ZDF_mixing_length} 251 252 \caption[Mixing length computation]{Illustration of the mixing length computation} 252 253 \label{fig:ZDF_mixing_length} … … 533 534 in \citet{reffray.guillaume.ea_GMD15} for the \NEMO\ model. 534 535 535 %% ================================================================================================= 536 \subsection[OSM: OSMosis boundary layer scheme (\forcode{ln_zdfosm})]{OSM: OSMosis boundary layer scheme (\protect\np{ln_zdfosm}{ln\_zdfosm})} 536 % ------------------------------------------------------------------------------------------------------------- 537 % OSM OSMOSIS BL Scheme 538 % ------------------------------------------------------------------------------------------------------------- 539 \subsection[OSM: OSMOSIS boundary layer scheme (\forcode{ln_zdfosm = .true.})] 540 {OSM: OSMOSIS boundary layer scheme (\protect\np{ln_zdfosm}{ln\_zdfosm})} 537 541 \label{subsec:ZDF_osm} 538 542 … … 543 547 \end{listing} 544 548 545 The OSMOSIS turbulent closure scheme is based on...... TBC 549 %-------------------------------------------------------------------------------------------------------------- 550 \paragraph{Namelist choices} 551 Most of the namelist options refer to how to specify the Stokes 552 surface drift and penetration depth. There are three options: 553 \begin{description} 554 \item \protect\np[=0]{nn_osm_wave}{nn\_osm\_wave} Default value in \texttt{namelist\_ref}. In this case the Stokes drift is 555 assumed to be parallel to the surface wind stress, with 556 magnitude consistent with a constant turbulent Langmuir number 557 $\mathrm{La}_t=$ \protect\np{rn_m_la} {rn\_m\_la} i.e.\ 558 $u_{s0}=\tau/(\mathrm{La}_t^2\rho_0)$. Default value of 559 \protect\np{rn_m_la}{rn\_m\_la} is 0.3. The Stokes penetration 560 depth $\delta = $ \protect\np{rn_osm_dstokes}{rn\_osm\_dstokes}; this has default value 561 of 5~m. 562 563 \item \protect\np[=1]{nn_osm_wave}{nn\_osm\_wave} In this case the Stokes drift is 564 assumed to be parallel to the surface wind stress, with 565 magnitude as in the classical Pierson-Moskowitz wind-sea 566 spectrum. Significant wave height and 567 wave-mean period taken from this spectrum are used to calculate the Stokes penetration 568 depth, following the approach set out in \citet{breivik.janssen.ea_JPO14}. 569 570 \item \protect\np[=2]{nn_osm_wave}{nn\_osm\_wave} In this case the Stokes drift is 571 taken from ECMWF wave model output, though only the component parallel 572 to the wind stress is retained. Significant wave height and 573 wave-mean period from ECMWF wave model output are used to calculate the Stokes penetration 574 depth, again following \citet{breivik.janssen.ea_JPO14}. 575 576 \end{description} 577 578 Others refer to the treatment of diffusion and viscosity beneath 579 the surface boundary layer: 580 \begin{description} 581 \item \protect\np{ln_kpprimix} {ln\_kpprimix} Default is \np{.true.}. Switches on KPP-style Ri \#-dependent 582 mixing below the surface boundary layer. If this is set 583 \texttt{.true.} the following variable settings are honoured: 584 \item \protect\np{rn_riinfty}{rn\_riinfty} Critical value of local Ri \# below which 585 shear instability increases vertical mixing from background value. 586 \item \protect\np{rn_difri} {rn\_difri} Maximum value of Ri \#-dependent mixing at $\mathrm{Ri}=0$. 587 \item \protect\np{ln_convmix}{ln\_convmix} If \texttt{.true.} then, where water column is unstable, specify 588 diffusivity equal to \protect\np{rn_dif_conv}{rn\_dif\_conv} (default value is 1 m~s$^{-2}$). 589 \end{description} 590 Diagnostic output is controlled by: 591 \begin{description} 592 \item \protect\np{ln_dia_osm}{ln\_dia\_osm} Default is \np{.false.}; allows XIOS output of OSMOSIS internal fields. 593 \end{description} 594 Obsolete namelist parameters include: 595 \begin{description} 596 \item \protect\np{ln_use_osm_la}\np{ln\_use\_osm\_la} With \protect\np[=0]{nn_osm_wave}{nn\_osm\_wave}, 597 \protect\np{rn_osm_dstokes} {rn\_osm\_dstokes} is always used to specify the Stokes 598 penetration depth. 599 \item \protect\np{nn_ave} {nn\_ave} Choice of averaging method for KPP-style Ri \# 600 mixing. Not taken account of. 601 \item \protect\np{rn_osm_hbl0} {rn\_osm\_hbl0} Depth of initial boundary layer is now set 602 by a density criterion similar to that used in calculating \emph{hmlp} (output as \texttt{mldr10\_1}) in \mdl{zdfmxl}. 603 \end{description} 604 605 \subsubsection{Summary} 606 Much of the time the turbulent motions in the ocean surface boundary 607 layer (OSBL) are not given by 608 classical shear turbulence. Instead they are in a regime known as 609 `Langmuir turbulence', dominated by an 610 interaction between the currents and the Stokes drift of the surface waves \citep[e.g.][]{mcwilliams.ea_JFM97}. 611 This regime is characterised by strong vertical turbulent motion, and appears when the surface Stokes drift $u_{s0}$ is much greater than the friction velocity $u_{\ast}$. More specifically Langmuir turbulence is thought to be crucial where the turbulent Langmuir number $\mathrm{La}_{t}=(u_{\ast}/u_{s0}) > 0.4$. 612 613 The OSMOSIS model is fundamentally based on results of Large Eddy 614 Simulations (LES) of Langmuir turbulence and aims to fully describe 615 this Langmuir regime. The description in this section is of necessity incomplete and further details are available in Grant. A (2019); in prep. 616 617 The OSMOSIS turbulent closure scheme is a similarity-scale scheme in 618 the same spirit as the K-profile 619 parameterization (KPP) scheme of \citet{large.ea_RG97}. 620 A specified shape of diffusivity, scaled by the (OSBL) depth 621 $h_{\mathrm{BL}}$ and a turbulent velocity scale, is imposed throughout the 622 boundary layer 623 $-h_{\mathrm{BL}}<z<\eta$. The turbulent closure model 624 also includes fluxes of tracers and momentum that are``non-local'' (independent of the local property gradient). 625 626 Rather than the OSBL 627 depth being diagnosed in terms of a bulk Richardson number criterion, 628 as in KPP, it is set by a prognostic equation that is informed by 629 energy budget considerations reminiscent of the classical mixed layer 630 models of \citet{kraus.turner_tellus67}. 631 The model also includes an explicit parametrization of the structure 632 of the pycnocline (the stratified region at the bottom of the OSBL). 633 634 Presently, mixing below the OSBL is handled by the Richardson 635 number-dependent mixing scheme used in \citet{large.ea_RG97}. 636 637 Convective parameterizations such as described in \ref{sec:ZDF_conv} 638 below should not be used with the OSMOSIS-OBL model: instabilities 639 within the OSBL are part of the model, while instabilities below the 640 ML are handled by the Ri \# dependent scheme. 641 642 \subsubsection{Depth and velocity scales} 643 The model supposes a boundary layer of thickness $h_{\mathrm{bl}}$ enclosing a well-mixed layer of thickness $h_{\mathrm{ml}}$ and a relatively thin pycnocline at the base of thickness $\Delta h$; Fig.~\ref{fig: OSBL_structure} shows typical (a) buoyancy structure and (b) turbulent buoyancy flux profile for the unstable boundary layer (losing buoyancy at the surface; e.g.\ cooling). 644 \begin{figure}[!t] 645 \begin{center} 646 %\includegraphics[width=0.7\textwidth]{ZDF_OSM_structure_of_OSBL} 647 \caption{ 648 \protect\label{fig: OSBL_structure} 649 The structure of the entraining boundary layer. (a) Mean buoyancy profile. (b) Profile of the buoyancy flux. 650 } 651 \end{center} 652 \end{figure} 653 The pycnocline in the OSMOSIS scheme is assumed to have a finite thickness, and may include a number of model levels. This means that the OSMOSIS scheme must parametrize both the thickness of the pycnocline, and the turbulent fluxes within the pycnocline. 654 655 Consideration of the power input by wind acting on the Stokes drift suggests that the Langmuir turbulence has velocity scale: 656 \begin{equation}\label{eq:w_La} 657 w_{*L}= \left(u_*^2 u_{s\,0}\right)^{1/3}; 658 \end{equation} 659 but at times the Stokes drift may be weak due to e.g.\ ice cover, short fetch, misalignment with the surface stress, etc.\ so a composite velocity scale is assumed for the stable (warming) boundary layer: 660 \begin{equation}\label{eq:composite-nu} 661 \nu_{\ast}= \left\{ u_*^3 \left[1-\exp(-.5 \mathrm{La}_t^2)\right]+w_{*L}^3\right\}^{1/3}. 662 \end{equation} 663 For the unstable boundary layer this is merged with the standard convective velocity scale $w_{*C}=\left(\overline{w^\prime b^\prime}_0 \,h_\mathrm{ml}\right)^{1/3}$, where $\overline{w^\prime b^\prime}_0$ is the upwards surface buoyancy flux, to give: 664 \begin{equation}\label{eq:vel-scale-unstable} 665 \omega_* = \left(\nu_*^3 + 0.5 w_{*C}^3\right)^{1/3}. 666 \end{equation} 667 668 \subsubsection{The flux gradient model} 669 The flux-gradient relationships used in the OSMOSIS scheme take the form: 670 % 671 \begin{equation}\label{eq:flux-grad-gen} 672 \overline{w^\prime\chi^\prime}=-K\frac{\partial\overline{\chi}}{\partial z} + N_{\chi,s} +N_{\chi,b} +N_{\chi,t}, 673 \end{equation} 674 % 675 where $\chi$ is a general variable and $N_{\chi,s}, N_{\chi,b} \mathrm{and} N_{\chi,t}$ are the non-gradient terms, and represent the effects of the different terms in the turbulent flux-budget on the transport of $\chi$. $N_{\chi,s}$ represents the effects that the Stokes shear has on the transport of $\chi$, $N_{\chi,b}$ the effect of buoyancy, and $N_{\chi,t}$ the effect of the turbulent transport. The same general form for the flux-gradient relationship is used to parametrize the transports of momentum, heat and salinity. 676 677 In terms of the non-dimensionalized depth variables 678 % 679 \begin{equation}\label{eq:sigma} 680 \sigma_{\mathrm{ml}}= -z/h_{\mathrm{ml}}; \;\sigma_{\mathrm{bl}}= -z/h_{\mathrm{bl}}, 681 \end{equation} 682 % 683 in unstable conditions the eddy diffusivity ($K_d$) and eddy viscosity ($K_\nu$) profiles are parametrized as: 684 % 685 \begin{align}\label{eq:diff-unstable} 686 K_d=&0.8\, \omega_*\, h_{\mathrm{ml}} \, \sigma_{\mathrm{ml}} \left(1-\beta_d \sigma_{\mathrm{ml}}\right)^{3/2} 687 \\\label{eq:visc-unstable} 688 K_\nu =& 0.3\, \omega_* \,h_{\mathrm{ml}}\, \sigma_{\mathrm{ml}} \left(1-\beta_\nu \sigma_{\mathrm{ml}}\right)\left(1-\tfrac{1}{2}\sigma_{\mathrm{ml}}^2\right) 689 \end{align} 690 % 691 where $\beta_d$ and $\beta_\nu$ are parameters that are determined by matching Eqs \ref{eq:diff-unstable} and \ref{eq:visc-unstable} to the eddy diffusivity and viscosity at the base of the well-mixed layer, given by 692 % 693 \begin{equation}\label{eq:diff-wml-base} 694 K_{d,\mathrm{ml}}=K_{\nu,\mathrm{ml}}=\,0.16\,\omega_* \Delta h. 695 \end{equation} 696 % 697 For stable conditions the eddy diffusivity/viscosity profiles are given by: 698 % 699 \begin{align}\label{diff-stable} 700 K_d= & 0.75\,\, \nu_*\, h_{\mathrm{ml}}\,\, \exp\left[-2.8 \left(h_{\mathrm{bl}}/L_L\right)^2\right]\sigma_{\mathrm{ml}} \left(1-\sigma_{\mathrm{ml}}\right)^{3/2} \\\label{eq:visc-stable} 701 K_\nu = & 0.375\,\, \nu_*\, h_{\mathrm{ml}} \,\, \exp\left[-2.8 \left(h_{\mathrm{bl}}/L_L\right)^2\right] \sigma_{\mathrm{ml}} \left(1-\sigma_{\mathrm{ml}}\right)\left(1-\tfrac{1}{2}\sigma_{\mathrm{ml}}^2\right). 702 \end{align} 703 % 704 The shape of the eddy viscosity and diffusivity profiles is the same as the shape in the unstable OSBL. The eddy diffusivity/viscosity depends on the stability parameter $h_{\mathrm{bl}}/{L_L}$ where $ L_L$ is analogous to the Obukhov length, but for Langmuir turbulence: 705 \begin{equation}\label{eq:L_L} 706 L_L=-w_{*L}^3/\left<\overline{w^\prime b^\prime}\right>_L, 707 \end{equation} 708 with the mean turbulent buoyancy flux averaged over the boundary layer given in terms of its surface value $\overline{w^\prime b^\prime}_0$ and (downwards) )solar irradiance $I(z)$ by 709 \begin{equation} \label{eq:stable-av-buoy-flux} 710 \left<\overline{w^\prime b^\prime}\right>_L = \tfrac{1}{2} {\overline{w^\prime b^\prime}}_0-g\alpha_E\left[\tfrac{1}{2}(I(0)+I(-h))-\left<I\right>\right]. 711 \end{equation} 712 % 713 In unstable conditions the eddy diffusivity and viscosity depend on stability through the velocity scale $\omega_*$, which depends on the two velocity scales $\nu_*$ and $w_{*C}$. 714 715 Details of the non-gradient terms in \eqref{eq:flux-grad-gen} and of the fluxes within the pycnocline $-h_{\mathrm{bl}}<z<h_{\mathrm{ml}}$ can be found in Grant (2019). 716 717 \subsubsection{Evolution of the boundary layer depth} 718 719 The prognostic equation for the depth of the neutral/unstable boundary layer is given by \citep{grant+etal18}, 720 721 \begin{equation} \label{eq:dhdt-unstable} 722 %\frac{\partial h_\mathrm{bl}}{\partial t} + \mathbf{U}_b\cdot\nabla h_\mathrm{bl}= W_b - \frac{{\overline{w^\prime b^\prime}}_\mathrm{ent}}{\Delta B_\mathrm{bl}} 723 \frac{\partial h_\mathrm{bl}}{\partial t} = W_b - \frac{{\overline{w^\prime b^\prime}}_\mathrm{ent}}{\Delta B_\mathrm{bl}} 724 \end{equation} 725 where $h_\mathrm{bl}$ is the horizontally-varying depth of the OSBL, 726 $\mathbf{U}_b$ and $W_b$ are the mean horizontal and vertical 727 velocities at the base of the OSBL, ${\overline{w^\prime 728 b^\prime}}_\mathrm{ent}$ is the buoyancy flux due to entrainment 729 and $\Delta B_\mathrm{bl}$ is the difference between the buoyancy 730 averaged over the depth of the OSBL (i.e.\ including the ML and 731 pycnocline) and the buoyancy just below the base of the OSBL. This 732 equation for the case when the pycnocline has a finite thickness, 733 based on the potential energy budget of the OSBL, is the leading term 734 \citep{grant+etal18} of a generalization of that used in mixed-layer 735 models e.g.\ \citet{kraus.turner_tellus67}, in which the thickness of the pycnocline is taken to be zero. 736 737 The entrainment flux for the combination of convective and Langmuir turbulence is given by 738 \begin{equation} \label{eq:entrain-flux} 739 {\overline{w^\prime b^\prime}}_\mathrm{ent} = -\alpha_{\mathrm{B}} {\overline{w^\prime b^\prime}}_0 - \alpha_{\mathrm{S}} \frac{u_*^3}{h_{\mathrm{ml}}} 740 + G\left(\delta/h_{\mathrm{ml}} \right)\left[\alpha_{\mathrm{S}}e^{-1.5\, \mathrm{La}_t}-\alpha_{\mathrm{L}} \frac{w_{\mathrm{*L}}^3}{h_{\mathrm{ml}}}\right] 741 \end{equation} 742 where the factor $G\equiv 1 - \mathrm{e}^ {-25\delta/h_{\mathrm{bl}}}(1-4\delta/h_{\mathrm{bl}})$ models the lesser efficiency of Langmuir mixing when the boundary-layer depth is much greater than the Stokes depth, and $\alpha_{\mathrm{B}}$, $\alpha_{S}$ and $\alpha_{\mathrm{L}}$ depend on the ratio of the appropriate eddy turnover time to the inertial timescale $f^{-1}$. Results from the LES suggest $\alpha_{\mathrm{B}}=0.18 F(fh_{\mathrm{bl}}/w_{*C})$, $\alpha_{S}=0.15 F(fh_{\mathrm{bl}}/u_*$ and $\alpha_{\mathrm{L}}=0.035 F(fh_{\mathrm{bl}}/u_{*L})$, where $F(x)\equiv\tanh(x^{-1})^{0.69}$. 743 744 For the stable boundary layer, the equation for the depth of the OSBL is: 745 746 \begin{equation}\label{eq:dhdt-stable} 747 \max\left(\Delta B_{bl},\frac{w_{*L}^2}{h_\mathrm{bl}}\right)\frac{\partial h_\mathrm{bl}}{\partial t} = \left(0.06 + 0.52\,\frac{ h_\mathrm{bl}}{L_L}\right) \frac{w_{*L}^3}{h_\mathrm{bl}} +\left<\overline{w^\prime b^\prime}\right>_L. 748 \end{equation} 749 750 Equation. \ref{eq:dhdt-unstable} always leads to the depth of the entraining OSBL increasing (ignoring the effect of the mean vertical motion), but the change in the thickness of the stable OSBL given by Eq. \ref{eq:dhdt-stable} can be positive or negative, depending on the magnitudes of $\left<\overline{w^\prime b^\prime}\right>_L$ and $h_\mathrm{bl}/L_L$. The rate at which the depth of the OSBL can decrease is limited by choosing an effective buoyancy $w_{*L}^2/h_\mathrm{bl}$, in place of $\Delta B_{bl}$ which will be $\approx 0$ for the collapsing OSBL. 751 546 752 547 753 %% ================================================================================================= … … 551 757 \begin{figure}[!t] 552 758 \centering 553 \includegraphics[width=0.66\textwidth]{ Fig_ZDF_TKE_time_scheme}759 \includegraphics[width=0.66\textwidth]{ZDF_TKE_time_scheme} 554 760 \caption[Subgrid kinetic energy integration in GLS and TKE schemes]{ 555 761 Illustration of the subgrid kinetic energy integration in GLS and TKE schemes and … … 663 869 \begin{figure}[!htb] 664 870 \centering 665 \includegraphics[width=0.66\textwidth]{ Fig_npc}871 \includegraphics[width=0.66\textwidth]{ZDF_npc} 666 872 \caption[Unstable density profile treated by the non penetrative convective adjustment algorithm]{ 667 873 Example of an unstable density profile treated by … … 808 1014 \begin{figure}[!t] 809 1015 \centering 810 \includegraphics[width=0.66\textwidth]{ Fig_zdfddm}1016 \includegraphics[width=0.66\textwidth]{ZDF_ddm} 811 1017 \caption[Diapycnal diffusivities for temperature and salt in regions of salt fingering and 812 1018 diffusive convection]{ … … 1286 1492 \begin{figure}[!t] 1287 1493 \centering 1288 \includegraphics[width=0.66\textwidth]{ Fig_ZDF_zad_Aimp_coeff}1494 \includegraphics[width=0.66\textwidth]{ZDF_zad_Aimp_coeff} 1289 1495 \caption[Partitioning coefficient used to partition vertical velocities into parts]{ 1290 1496 The value of the partitioning coefficient (\cf) used to partition vertical velocities into … … 1326 1532 \begin{figure}[!t] 1327 1533 \centering 1328 \includegraphics[width=0.66\textwidth]{ Fig_ZDF_zad_Aimp_overflow_frames}1534 \includegraphics[width=0.66\textwidth]{ZDF_zad_Aimp_overflow_frames} 1329 1535 \caption[OVERFLOW: time-series of temperature vertical cross-sections]{ 1330 1536 A time-series of temperature vertical cross-sections for the OVERFLOW test case. … … 1406 1612 \begin{figure}[!t] 1407 1613 \centering 1408 \includegraphics[width=0.66\textwidth]{ Fig_ZDF_zad_Aimp_overflow_all_rdt}1614 \includegraphics[width=0.66\textwidth]{ZDF_zad_Aimp_overflow_all_rdt} 1409 1615 \caption[OVERFLOW: sample temperature vertical cross-sections from mid- and end-run]{ 1410 1616 Sample temperature vertical cross-sections from mid- and end-run using … … 1419 1625 \begin{figure}[!t] 1420 1626 \centering 1421 \includegraphics[width=0.66\textwidth]{ Fig_ZDF_zad_Aimp_maxCf}1627 \includegraphics[width=0.66\textwidth]{ZDF_zad_Aimp_maxCf} 1422 1628 \caption[OVERFLOW: maximum partitioning coefficient during a series of test runs]{ 1423 1629 The maximum partitioning coefficient during a series of test runs with … … 1430 1636 \begin{figure}[!t] 1431 1637 \centering 1432 \includegraphics[width=0.66\textwidth]{ Fig_ZDF_zad_Aimp_maxCf_loc}1638 \includegraphics[width=0.66\textwidth]{ZDF_zad_Aimp_maxCf_loc} 1433 1639 \caption[OVERFLOW: maximum partitioning coefficient for the case overlaid]{ 1434 1640 The maximum partitioning coefficient for the \forcode{nn_rdt=10.0} case overlaid with … … 1437 1643 \end{figure} 1438 1644 1439 \ onlyinsubfile{\input{../../global/epilogue}}1645 \subinc{\input{../../global/epilogue}} 1440 1646 1441 1647 \end{document}
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