# Changeset 10614

Ignore:
Timestamp:
2019-01-31T18:10:55+01:00 (14 months ago)
Message:

Merge of changeset [10613] into the trunk

Location:
NEMO/trunk/doc/latex/NEMO
Files:
3 edited

### Legend:

Unmodified
 r10530 %----------------------------------------------------------------------------------------------- Options are defined through the \ngn{nambdy\_tide} namelist variables for reading in the complex harmonic amplitudes of elevation (ssh) and barotropic velocity (u,v). The tidal harmonic data can be specified in 2 ways.\\ First it can be specified on a 2D grid covering the entire model domain in which case the user should set \np{ln\_bdytide\_2ddta }\forcode{ = .true.}. In this case the model assumes that the real and imaginary parts are split. The variable naming convention is \textit{constituent\_name\_z1} for real SSH and \textit{constituent\_name\_z2} for imaginary SSH. The available \textit{constituent\_names} in NEMO are defined in \rou{SBC/tide.h90} Likewise for $u$ and $v$ data. File name is assumed to be \np{filtide}\ifile{\_grid\_T} for the elevation component and \np{filtide}\ifile{\_grid\_U} for the u barotropic velocity and \np{filtide}\ifile{\_grid\_V} for the v barotropic velocity.\\ Otherwise, the tidal data must be specified along bdy segments. In this case each constituent has its own file name and the real part is assumed to be z1 and the imaginary part z2 for SSH. Similarly u1, u2 and v1, v2 for velocities. Input file name convention (for elevation of the M2 tidal component) is \np{filtide}\ifile{M2\_grid\_T}. Similar logic applies for other components and u and v barotropic velocities.\\ The data may also be in complex conjugate form. If that is the case then the user should set \np{ln\_bdytide\_conj}\forcode{ = .true. } so the model correctly interprets the data. The default case assumes it is not in complex conjugate form. Note the barotropic velocities are assumed to be on the model native grid and must be rotated as appropriate from the source grid upon which they are extracted from. To do so convert to U, V amplitude and phase into tidal ellipses. Add the grid rotation to ellipse inclination and convert back. Be careful about conventions of direction of rotation, e.g. anticlockwise or clockwise. Tidal forcing at open boundaries requires the activation of surface tides (i.e., in \ngn{nam\_tide}, \np{ln\_tide} needs to be set to \forcode{.true.} and the required constituents need to be activated by including their names in the \np{cname} array; see \autoref{sec:SBC_tide}). Specific options related to the reading in of the complex harmonic amplitudes of elevation (SSH) and barotropic velocity (u,v) at open boundaries are defined through the \ngn{nambdy\_tide} namelist parameters.\\ The tidal harmonic data at open boundaries can be specified in two different ways, either on a two-dimensional grid covering the entire model domain or along open boundary segments; these two variants can be selected by setting \np{ln\_bdytide\_2ddta } to \forcode{.true.} or \forcode{.false.}, respectively. In either case, the real and imaginary parts of SSH and the two barotropic velocity components for each activated tidal constituent \textit{tcname} have to be provided separately: when two-dimensional data is used, variables \textit{tcname\_z1} and \textit{tcname\_z2} for real and imaginary SSH, respectively, are expected in input file \np{filtide} with suffix \ifile{\_grid\_T}, variables \textit{tcname\_u1} and \textit{tcname\_u2} for real and imaginary u, respectively, are expected in input file \np{filtide} with suffix \ifile{\_grid\_U}, and \textit{tcname\_v1} and \textit{tcname\_v2} for real and imaginary v, respectively, are expected in input file \np{filtide} with suffix \ifile{\_grid\_V}; when data along open boundary segments is used, variables \textit{z1} and \textit{z2} (real and imaginary part of SSH) are expected to be available from file \np{filtide} with suffix \ifile{tcname\_grid\_T}, variables \textit{u1} and \textit{u2} (real and imaginary part of u) are expected to be available from file \np{filtide} with suffix \ifile{tcname\_grid\_U}, and variables \textit{v1} and \textit{v2} (real and imaginary part of v) are expected to be available from file \np{filtide} with suffix \ifile{tcname\_grid\_V}. If \np{ln\_bdytide\_conj} is set to \forcode{.true.}, the data is expected to be in complex conjugate form. Note that the barotropic velocity components are assumed to be defined on the native model grid and should be rotated accordingly when they are converted from their definition on a different source grid. To do so, the u, v amplitudes and phases can be converted into tidal ellipses, the grid rotation added to the ellipse inclination, and then converted back (care should be taken regarding conventions of the direction of rotation). %, e.g. anticlockwise or clockwise. \biblio
 r10468 The tidal forcing, generated by the gravity forces of the Earth-Moon and Earth-Sun sytems, is activated if \np{ln\_tide} and \np{ln\_tide\_pot} are both set to \np{.true.} in \ngn{nam\_tide}. is activated if \np{ln\_tide} and \np{ln\_tide\_pot} are both set to \forcode{.true.} in \ngn{nam\_tide}. This translates as an additional barotropic force in the momentum equations \ref{eq:PE_dyn} such that: $+g\nabla (\Pi_{eq} + \Pi_{sal})$ where $\Pi_{eq}$ stands for the equilibrium tidal forcing and $\Pi_{sal}$ a self-attraction and loading term (SAL). where $\Pi_{eq}$ stands for the equilibrium tidal forcing and $\Pi_{sal}$ is a self-attraction and loading term (SAL). The equilibrium tidal forcing is expressed as a sum over the chosen constituents $l$ in \ngn{nam\_tide}. The constituents are defined such that \np{clname(1) = 'M2', clname(2)='S2', etc...}. For the three types of tidal frequencies it reads: \\ Long period tides : $\Pi_{eq}(l)=A_{l}(1+k-h)(\frac{1}{2}-\frac{3}{2}sin^{2}\phi)cos(\omega_{l}t+V_{l})$ diurnal tides : $\Pi_{eq}(l)=A_{l}(1+k-h)(sin 2\phi)cos(\omega_{l}t+\lambda+V_{l})$ Semi-diurnal tides: $\Pi_{eq}(l)=A_{l}(1+k-h)(cos^{2}\phi)cos(\omega_{l}t+2\lambda+V_{l})$ Here $A_{l}$ is the amplitude, $\omega_{l}$ is the frequency, $\phi$ the latitude, $\lambda$ the longitude, $V_{0l}$ a phase shift with respect to Greenwich meridian and $t$ the time. The Love number factor $(1+k-h)$ is here taken as a constant (0.7). The SAL term should in principle be computed online as it depends on the model tidal prediction itself (see \citet{Arbic2004} for a discussion about the practical implementation of this term). Nevertheless, the complex calculations involved would make this computationally too expensive. Here, practical solutions are whether to read complex estimates $\Pi_{sal}(l)$ from an external model (\np{ln\_read\_load=.true.}) or use a scalar approximation'' (\np{ln\_scal\_load=.true.}). In the latter case, it reads:\\ $\Pi_{sal} = \beta \eta$ where $\beta$ (\np{rn\_scal\_load}, $\approx0.09$) is a spatially constant scalar, often chosen to minimize tidal prediction errors. Setting both \np{ln\_read\_load} and \np{ln\_scal\_load} to false removes the SAL contribution. The equilibrium tidal forcing is expressed as a sum over a subset of constituents chosen from the set of available tidal constituents defined in file \rou{SBC/tide.h90} (this comprises the tidal constituents \textit{M2, N2, 2N2, S2, K2, K1, O1, Q1, P1, M4, Mf, Mm, Msqm, Mtm, S1, MU2, NU2, L2}, and \textit{T2}). Individual constituents are selected by including their names in the array \np{clname} in \ngn{nam\_tide} (e.g., \np{clname(1) = 'M2', clname(2)='S2'} to select solely the tidal consituents \textit{M2} and \textit{S2}). Optionally, when \np{ln\_tide\_ramp} is set to \forcode{.true.}, the equilibrium tidal forcing can be ramped up linearly from zero during the initial \np{rdttideramp} days of the model run. The SAL term should in principle be computed online as it depends on the model tidal prediction itself (see \citet{Arbic2004} for a discussion about the practical implementation of this term). Nevertheless, the complex calculations involved would make this computationally too expensive.  Here, two options are available: $\Pi_{sal}$ generated by an external model can be read in (\np{ln\_read\_load=.true.}), or a scalar approximation'' can be used (\np{ln\_scal\_load=.true.}). In the latter case $\Pi_{sal} = \beta \eta,$ where $\beta$ (\np{rn\_scal\_load} with a default value of 0.094) is a spatially constant scalar, often chosen to minimize tidal prediction errors. Setting both \np{ln\_read\_load} and \np{ln\_scal\_load} to \forcode{.false.} removes the SAL contribution. % ================================================================