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Contact: wbrown@umassd.edu



An Observational / Modeling Study of Wintertime Convection
and Water Mass Formation
(CONVEX)

Wendell S. Brown and Frank L. Bub
Ocean Process Analysis Laboratory and Department of Earth Sciences
University of New Hampshire
Durham, NH 03824


Donald Denbo
Pacific Marine Environmental Laboratory
Seattle, WA 98115



ABSTRACT



Wintertime atmospherically forced convective overturning (and subsequent mixing) has been shown to be responsible for significant deep water formation in the Greenland Sea, the Labrador Sea, the western Mediterranean and elsewhere in the polar regions. Observational evidence suggests that related wintertime water mass formation processes are also active in the Gulf of Maine.

We are using the Gulf of Maine as a convenient environmental laboratory in which to explore the physics of overturning and mixing with a combined observational/modeling program called CONVEX (for Convection Experiment). This research addresses some basic questions concerning the kinematics and energetics of mixed layer formation in winter with an emphasis on water column convective instability, sinking and mixing in the presence of wind mixing.

The observations, which cannot resolve all the scales of this process, are being integrated with the results of a numerical non-hydrostatic Ocean Large Eddy Model (OLEM) to provide new insight into the role of small scale convection in wintertime water mass formation. A pair of field experiments consisting of moored array and hydrographic IADCP, observations augmented by operational meteorological and satellite SST imagery, were conducted during the winters of 1996-97 and 1997-98.

The first was in shallower coastal water of Jeffreys Basin where the convective plumes interact with the ocean bottom. The second was in deeper offshore water of Wilkinson Basin, where convection does not reach the bottom.

A temperature / conductivity chain, a pair of temperature chains, ADCP current profilers, and surface weather instrumentation provided temporal/spatial information on the small scale convective plumes and mixed layer depth. The spatial / temporal basin-scale information is being derived from hydrography surveys and satellite SST imagery. These observations are being used to assess the fidelity of the results from a series of OLEM model experiments designed to (a) model "typical" convective plumes and (b) determine the relative importance of convection and wind mixing in the watermass formation process. The observations are also being used to relate the structure and intensity of convective overturning to winter mixed layer and water mass formation.