Fall 1998

We recently developed a three-dimensional primitive equation numerical model known as CANDIE (CANadian version of the DIEcast model) and applied it to the eastern seaboard including the Gulf of St. Lawrence, Scotian Shelf and Gulf of Maine. Our immediate goal is to simulate the multiple-year circulation of the region, allowing the density field to evolve with the flow. We were encouraged to find the predicted circulation pattern reproduces many of the observed features including relatively strong coastal currents over the Gaspe the Scotian Shelf, strong along-isobath shelf break currents and eddies in deep water spun off the Gulf Stream.

At high wind speeds, one major problem with the buoys is inadequate and unreliable measurements of wind speeds. Because the buoy is often sheltered by the waves, it fails to measure wind speeds correctly. Therefore, "sea truth" is no longer a valid calibration criterion. We discuss the behaviour of buoys of different shapes and sensor heights at rough sea states.

The purpose of this study is to present the capacities offered by coupled atmospheric and hydrologic models as a new tool to validate and interpret results produced by atmospheric models. The advantages offered by the stream flow observations are different from those offered by conventional precipitation observations. It is demonstrated that the dependence effect between basins and sub-basins can be very useful, and that the precipitation integrator effect of the larger basins facilitates the evaluation of state-of-the-science atmospheric models by filtering out some of the spatial and temporal variability that complicate the point-by-point verifications that are more commonly used. The stream flow permits a better estimate of the water amount fallen over a region. Comparing the stream flow predicted by the coupled atmospheric-hydrologic model versus the measured stream flow proves to be sufficiently sensitive to clearly assess atmospheric model improvements resulting from increasing the horizontal resolution and altering the treatment of precipitation processes in the model.

Abstract. The CANDIE (Canadian version of Diecast) ocean model has recently been modified to include a free surface. In this talk I will present results from two experiments using the CANDIE model. The first experiment deals with an idealized situation in which (i) the flow field varies only in the vertical and one horizontal direction (ii) water depth is constant in both the deep and shallow water and with a linearly sloping shelf break in between (iii) the density is initially uniform horizontally with constant vertical gradient (iv) perturbations are so small that most nonlinear terms can be dropped from the model. I will show that the results from CANDIE are in good agreement with analytic solutions obtained using the linear theory of Craig (1987). In the second experiment we apply the fully nonlinear, three-dimensional model to the Gulf of St. Lawrence using a summer density climatology to initialize the model's density field. The boundary conditions are obtained using an incremental data assimilation method in which a linear shallow water model is used to minimize the difference between observed and predicted sea surface elevations using the adjoint method. The model generated co-amplitude and co-tidal charts agree well with the assimilated tidal amplitudes and phases. More encouragingly the predicted tidal currents are in good agreement with an independent set of current measurements.

The upper waters on the either of the Subpolar Front have different tendencies and dominant scales of the interannual-to-interdecadal variability.

The Labrador Sea Water (LSW) has greatly changed both its properties and distribution over time. It reached a maximum in temperature and salinity in the late 60s - early 70s, while during the 90s it has become colder, fresher, denser and deeper than at any time in this century. The tendency changed around 1994 and now the LSW is steadily getting warmer, saltier and lighter.

Between the early 70's and 90's North-East Atlantic Deep Water (NEADW) and Denmark Strait Overflow (DSOW) also became colder and fresher over a large portion of the North-West Atlantic.

The remnants of Antarctic Bottom Water (ABW) entering the subpolar gyre have been getting colder in the past two decades, but the rate of this change was less than that for DSOW, resulting in a change of spatial gradients in the bottom layer.

The change in the the properties of the upper, intermediate and deep waters throughout the North Atlantic resulted in changes of dynamic heights and potential vorticity, those of a great importance for understanding and modelling the ocean dynamics.