ADCIRC2D+

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ADCIRC2D+, is a mode which allows for the inclusion of baroclinic (density-driven) effects into the traditionally barotropic (depth-averaged) system. This is achieved by coupling ADCIRC with temperature and salinity fields from a coarser-resolution Ocean General Circulation Model (OGCM), enabling improved representation of long-term sea level dynamics. Description of results using this capability are available in (Pringle et al. 2019) and (Blakely et al. 2024)

Version

ADCIRC version:

≥ 56

Some of the capability of ADCIRC2D+ is available in v55; however improvements and modifications were made that are present only in v56 and above.

Governing Equations

ADCIRC2D+ solves a modified form of the shallow water equations using the Generalized Wave Continuity Equation (GWCE). The momentum equation includes baroclinic and internal tide drag terms: ${\frac {\partial \mathbf {U} }{\partial t}}+\mathbf {U} \cdot \nabla \mathbf {U} +f\mathbf {k} \times \mathbf {U} =-\nabla \left({\frac {p_{s}}{\rho _{0}}}+g(\eta -\eta _{EQ}-\eta _{SAL})\right)-{\frac {\text{BPG}}{H}}+{\frac {{\boldsymbol {\tau }}_{s}-{\boldsymbol {\tau }}_{b}}{\rho _{0}H}}-\gamma _{D}\mathbf {C} \mathbf {U}$

Where:

• BPG is the depth-integrated baroclinic pressure gradient
• γ_D is a scaling parameter for internal wave drag
• C is the internal wave drag tensor

The baroclinic pressure gradient is computed as: ${\text{BPG}}={\frac {g}{\rho _{0}}}\left[\int _{-h}^{0}\nabla \left(\int _{0}^{z}(\rho -\rho _{0})\,dz'\right)dz+\eta \nabla [\eta (\rho _{s}-\rho _{0})]\right]$

The internal tide drag tensor is scaled using a dissipation ratio $\gamma _{D}$ defined by: $\gamma _{D}={\frac {{\text{Diss}}_{\text{tidal}}}{{\text{Diss}}_{\text{total}}}}={\frac {\mathbf {U} _{\text{tidal}}\cdot \mathbf {C} \cdot \mathbf {U} _{\text{tidal}}}{\mathbf {U} \cdot \mathbf {C} \cdot \mathbf {U} }}$

Tidal velocity is estimated using a lagged 25-hour filter and removing the resultant mean signal from the total velocity. This ensures that dissipation from internal wave drag occurs predominantly at tidal frequencies, preserving tidal fidelity in the coupled model.

Density Control Namelist

Activating ADCIRC2D+ is accomplished through the use of the densityControl namelist.