Model Initialization in a Tidally Energetic Regime: a Dynamically Adjusted Objective Analysis.

A simple improvement to objective analysis of hydrographic data is proposed to eliminate spatial aliasing effects in tidally energetic regions. The proposed method consists of the evaluation of anomalies from observations with respect to circulation model fields. The procedure is run iteratively to achieve convergence. The method is applied in the Bay of Fundy and compared with traditional objective analysis procedures and dynamically adjusted climatological fields. The hydrographic skill (difference between observed and model temperature and salinity) of the dynamically adjusted objective analysis is significantly improved by reducing bias and correcting the vertical structure. Representation of the observed velocities is also improved. The resulting flow is consistent with the known circulation in the Bay.

Model Simulations of the Bay of Fundy Gyre: 2. Hindcasts for 2005-2007 Reveal Interannual Variability in Retentiveness.

A persistent gyre at the mouth of the Bay of Fundy results from a combination of tidal rectification and buoyancy forcing (Aretxabaleta et al., J. Geophys. Res., vol. 113, 2008). Here we assess interannual variability in the strength of the gyre using data assimilative model simulations. Realistic hindcast representations of the Gyre are considered over the course of cruise surveys in 2005, 2006 and 2007. Assimilation of shipboard and moored ADCP velocities are used to improve the skill of the simulations, as quantified by comparison with non-assimilated drifter trajectories. Our hindcast suggest a weakening of the Gyre system during May 2005. Retention of simulated passive particles in the Gyre during that period was highly reduced. A recovery of the dense water pool in the deep part of the basin by June 2006 resulted in a return to particle retention characteristics similar to climatology. Retention estimates reached a maximum during May 2007 (sub-surface) and June-July 2007 (near-surface). Interannual variability in the strength of the gyre was primarily modulated by the stratification of the dense water pool inside the Grand Manan Basin. These changes in stratification may be attributed to mixing conditions the preceding fall/winter and/or advectively-driven modification of water mass properties.

Model Simulations of the Bay of Fundy Gyre: 1. Climatological Results.

The characteristics of a persistent gyre in the mouth of the Bay of Fundy are studied using model simulations. A set of climatological runs are conducted to evaluate the relative importance of the different forcing mechanisms affecting the gyre. The main mechanisms are tidal rectification, and density-driven circulation. Stronger circulation of the gyre occurs during the later part of the stratified season (July-August and September-October). The density-driven flow around the gyre is set-up by weak tidal mixing in the deep basin in the central Bay of Fundy and strong tidal mixing on the shallow flanks around Grand Manan Island and western Nova Scotia. Retention of particles in the Gyre is controlled by the residual tidal circulation, increased frontal retention during stratified periods, wind stress, and interactions with the adjacent circulation of the Gulf of Maine. Residence times longer than 30 days are predicted for particles released in the proximity of the gyre.