A Latent-and Sensible-Heat Polynya Model for the North Water, Northern Baffin Bay

Abstract

The Pease latent-heat polynya model is coupled to a reduced-gravity, coastal upwelling model in order to simulate the formation and maintenance of the North Water (NOW), the Arctic's largest polynya, located in northern Beffin Bay. In this region, strong northerly winds during winter and spring drive ice southward as fast as it is produced locally (the Pease mechanism for polynya formation), and also produce upwelling of warm subsurface water along the west coast of Greenland. This upwelling provides an upward heat flux that melts ice near the coast (a sensible-host mechanism for polynya formation). This combined latent- and sensible-heat polynya model is formulated as an initial-boundary value problem with uniform winds. Its solution gives the tide evolution of the upper-layer velocity and depth, and also the polynya width as measured southward from the northern boundary of the polynya. There are two fundamental time scales in the problem: a fast one (of the order of days) that characterizes the polynya opening by the Pease mechanism, and a slow one (of the order of weeks) dust describes the evolution of the upwelling of warn subsurface water along the Greenland coast and hence the gradual southward extension of the ice edge in this region via the sensible-heat mechanism for polynya formation. The steady-state (asymptotic or limiting) polynya width is a strong function of the air temperature, but a weak function of the wind speed. The model results show that in the upwelling region near the Greenland coast, the limiting polynya width is considerably larger than farther offshore, where it is a constant (the limiting Pease width). This ice-edge configuration is in general agreement with that seen in recent Landsat satellite images of the NOW. For a spatially varying wind field. the southern ice edge of the NOW has an offshore profile similar to that of the wind stress forcing. In a north-south channel domain formulation of the model, upwelling occurs in the eastern part (i.e., near Greenland) and downwelling in the western part (near Ellesmere Island). Thus, the polynya is wider near Greenland and narrower near the Canadian islands.