# New URL for NEMO forge! http://forge.nemo-ocean.eu

Since March 2022 along with NEMO 4.2 release, the code development moved to a self-hosted GitLab.
This present forge is now archived and remained online for history.
Changeset 10613 for NEMO/releases/release-4.0/doc/latex/NEMO/subfiles/chap_SBC.tex – NEMO

# Changeset 10613 for NEMO/releases/release-4.0/doc/latex/NEMO/subfiles/chap_SBC.tex

Ignore:
Timestamp:
2019-01-31T17:38:13+01:00 (4 years ago)
Message:

Revision of two subsections on tidal forcing and update of the list of NEMO System Team members in the NEMO manual

File:
1 edited

### Legend:

Unmodified
 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. % ================================================================