The Maine coastal current: spring climatological circulation

Computational results are presented for the climatological circulation in the Gulf of Maine, with special emphasis on its coastal current in the periods March-April and May-June. The simulations use a 3-D prognostic Finite Element model. The computational domain includes the entire Gulf plus adjacent waters, with a higher resolution coastal domain nested within. A series of six bimonthly Gulf-wide simulations establishes the spring conditions within the annual climatological cycle. The distinctive Gulf of Maine cyclonic circulation is persistent, with significant bimonthly modulation of key Maine coastal current features. In all cases there is a significant barotropic pressure variation of order 5 cm along the margin of the coastal current, accompanying detailed, variable interactions between it and the interior Gulf. In the spring periods of emphasis, a well-developed coastal current is present. Numerical drifters generally confirm the existence of branch points south of Penobscot Bay, east of Cape Ann, and at Great South Channel. Important differences between the March-April and May-June circulation are apparent. In particular, both the offshore transport at the Penobscot branch point and the along-shore transport at Cape Ann are strong, dominant features in March-April; both are weak in May-June. The more highly resolved, nested calculations replicate the general structure of the Gulf-wide circulation provided the correct boundary conditions are applied, confirming the pervasive dynamical influence of the Gulf-scale circulation on the coastal current. The nested calculations also expose finer structure due to river sources, heat flux, and topographic refinement. The separate influences of local (tidal rectification, local wind, local baroclinicity, river discharges) and remote (Gulf-scale) forcing are examined. Tidal rectification in the Eastern Gulf and wind-driven return flow near-shore are both important contributors to the details of the coastal current. Local baroclinicity is critical and must be in balance with the offshore pressure conditions; otherwise unrealistic exchanges with the Gulf occur. An approximate division of local and remote dynamical regimes lies near the 100-m isobath. Implications are drawn for future modeling studies.