Marine Ecosystem Dynamics Modeling Laboratory

Tidal Simulation

The GoM/GB FVCOM is the model that has accurately resolved the resonance nature of the M2 tide in the Bay of Fundy. The computed tidal elevation and currents were compared directly with all available observational data in the GoM. The model predicted that the surface tide propagated into the GoM from the open ocean and turned clockwise to the northeast with an amplitude increase from 50 cm over GB to over 400 cm or higher in the Bay of Fundy. The tidal phase was almost parallel to the major axis of GB and then turned clockwise within the GoM. The model-predicted spatial distributions of co-amplitude and co-phase are in good agreement with observed co-tidal charts.

1. Tidal animation

This animation was made by the surface tidal current vectors and sea level interpolated from unstructured grids to regular grids (animation 1). Part of the Cape Code was not resolved in this animation due to the coarse grid interpolation when the OpenDX was used to create the movie.

Click the image on the right to view a 2-D animation of M2 tidal elevation and surface tidal currents. This animation was made with selected node points to make it viewable on the website screen resolution.


3-D Tidal Animation

2. On-line Tidal Forecast

This forecast system was built based on the Foreman (1979) tidal harmonic analysis program consisting of eight major tidal constituents (M2, S2, N2, K2, O1, K1, P1, Q1) (Click the image on the right to go onto this system). The harmonic constants used to drive this system were calculated using the best tidal simulation results of FVCOM (calibrated with all observational data).


Gulf of Maine Tidal Forcasting

3. Tidal Elevations

1. Comparison between observed and model-predicted amplitudes and phases of the M2, S2, N2, O1, and K1 tidal elevations (Figs. 1-5). Red solid line: amplitude (cm); blue dashed line: phase (degree G);

2. Comparison between observed and model-predicted ellipses of the M2, S2, N2, O1, and K1 tidal currents (Figs. 6-10).

4. Tidal Residual Circulation

Observations have revealed that the nonlinear interaction of tidal current over the abrupt bottom topography of Georges Bank (GB) generates a clockwise residual current on GB (Butman et al., 1982; Limeburner and Beardsley, 1996). This current tends to flow eastward as a jet of 20-30 cm/s on the northern flank and re-circulate westward as a relatively weak, broad current of about 1-5 cm/s on the southern flank. Previous theoretical and numerical modeling studies suggest that the strong current jet formed on the northern flank is a result of (1) nonlinear interaction of barotropic tidal current with variable bottom topography (Loder 1980; Greenberg, 1983), (2) seasonal intensification of tidal mixing front (Chen, 1992; Naimie et al. 1994; Chen et al. 1995, 2001; Naimie, 1996) and (3) nonlinear interaction between barotropic and internal tidal currents and between internal tidal currents (Chen and Beardsley,1995, 1998).

Driven by the M2 tidal forcing, FVCOM predicts a topographically-controlled clockwise residual circulation around GB and Browns Bank (BB) and a strong southward residual current over NS (Fig. 11). Over GB, the water flowed eastward to southeastward as a strong jet with a maximum speed of about 20-30 cm/s along the local isobath on the northern flank, then flowed to the southern flank along two main paths between the 40 to 60-m isobaths and along the 100-m isobath as relatively weak and broader flows with maximum speeds of about 3-5 cm/s. These weak flows then turn back (recirculate) to the northwest and northern flanks mainly along the 40 to 60-m isobaths. The residual current was surface-intensified, and significant upwelling of about 0.01 cm/s was found on the slope of the northern flank.


Fig 11: The distribution of the M2 residual current on Georges Bank.

Unlike the model results shown in our previous model efforts with POM/ECOM-si (Chen et al., 2001), the FVCOM-predicted residual currents flow mainly along the local isobaths, while POM/ECOM-si shows a significant on-bank flow on the northern flank. Although both the models show an eastward current around 40- to 100-m isobath on the northern flank, the residual current predicted by FVCOM is about one order of magnitude larger than that predicted by ECOM-si. The long-term current measurement data indicate that the tidal rectified current jet at the northern flank is directed parallel to the local isobath (Butman et al., 1982). The magnitude and direction of this current jet were well captured by FVCOM, but not by POM/ECOM-si. Inflexibility of the structure grids used in POM/ECOM-si makes it difficult to build high resolution grids locally to resolve the current jet on the northern flank. This is one of the key reasons why POM/ECOM-si-predicted residual currents are weaker and also shifted on-bank-ward.

5. Model-data comparison tables

Click here to download or view pdf format tables of the observed and model-computed surface elevation comparison for 5 major tidal constituents in the Gulf of Maine (GoM) (M2, N2, S2, K1 and O1). The comparison was made at 98 tidal measurement sites available around the coast and interior of GoM.

Click tidal symbols below to download or view pdf format tables of the observed and model-computed tidal ellipse comparison for 5 major tidal constituents in the Gulf of Maine (GoM) (M2, N2, S2, K1 and O1). The comparison was made at 98 tidal measurement sites available around the coast and interior of GoM.

 

M2

 

S2 N2 K1 O1

Posted on January 17, 2014