Please find below an updated analysis of the Mass. and Cape Cod Bays general multiscale circulation (Sep 23). The discussion is based on the best current field estimate product, which uses all hydrographic and wind forcing data collected up to Sep 21 and is forced by forecast winds beyond, up to Sep 24.
We have now analyzed the circulation from early September up to present (Sep 21), including forecasts from Sep 22 until Sep 24. During this time period, we have observed all of the previously described circulation features, as well as new ones. Several of them have not been previously described in the literature.
The additional variability features range in size from sub-mesoscale and mesoscale to bay-scale. These include an anticyclone-cyclone pair, with the anticyclone in Northern Mass Bay and the cyclone in Cape Cod Bay. An elongated Mass Bay anticyclone evolves from bay-scale to half bay-scale (located over Cape Cod Bay and center of Mass Bay). An interesting mesoscale feature formed off Cape Ann moves to the south and stops over the topographic depression north of Stellwagen Bank for several days.
Two dynamical processes are noteworthy. One is the formation of submesoscale vortices between branches and filaments of the buoyancy GOM current and/or mesoscale gyres. The second is the apparent control of the structure of the buoyancy flow by the strong wind events. For example, the classical picture of the southward rim current and associated cyclonic Mass Bay circulation gyre can be set-up by northerly winds which feed the upwelling zone from Race Point to Dennis, via a deep eastward flow. Whereas southerly winds, feeding the Sandwich to Scituate upwelling, can destroy the surface rim current and set-up the anticyclonic flow in Mass Bay, via a deep westward flow. For several days following strong wind events, the structure of the buoyancy current is maintained by a combination of inertia, topography, coastal geometry and internal dynamics.
The GOM buoyancy circulation has a triple branching point off Cape Ann, but either one, two or three branches can be present. The first branch is the Mass Bay coastal current. The second branch flows north and then turns westward into Stellwagen Basin and then out at Race Point. The third branch is the external one, flowing around the GOM as a coastal current and bordering Mass Bay along Stellwagen Bank (without entering the Bay).
Plots of these evolving features and simplified cartoons of the main buoyancy-wind-driven circulation at 10 m will be made available sometime tomorrow.