My research during the period 1999-2000 has focused on three main areas: (1) circulation and associated seasonal availability over the eastern Canadian shelf, (2) development of a simple data assimilation technique to improve the utility of the ocean models, and (3) major pathways of passive tracers in the northwest Atlantic Ocean. The ocean model used in these studies is the three-dimensional primitive-equation ocean model known as CANDIE. It was developed originally by Sheng, Wright, Greatbatch and Dietrich (1998). Recent modifications of the model code include a free-surface, partial cells and equations for passive tracers.
The Gaspé Current is a buoyancy-driven, narrow coastal jet flowing seaward along the coast of the Gaspé Peninsula. It is one of the most profound features of near surface circulation in the northwest Gulf of St. Lawrence. The Gaspé Current often becomes unstable with the occurrence of unstable wave features. The dynamics of the instability development in the Gaspé Current are not yet fully understood. The high-resolution CANDIE model was applied to the northwest Gulf of St. Lawrence to study the nonlinear dynamics of the Gaspé Current driven by river discharge and boundary flows. The coastal current initially follows the coastline but later becomes unstable with many backward-breaking waves developed along the outer edge of the current, highly consistent with the wavelike motion of the Gaspé Current inferred from satellite images of sea surface temperature.
CANDIE was also used in the study of the seasonal variability of hydrography and circulation in the Gulf of St. Lawrence and Scotian Shelf (Sheng, Thompson, Dowd and Petrie, 2001). The model was run in diagnostic mode with temperatures and salinities interpolated linearly from the two nearest seasonal mean fields. The model reproduces many of the important circulation features in this region, including a year-around cyclonic gyre over the northwestern GSL, southeastward outflow through the western Cabot Strait, and southwestward flow on the Scotian Shelf with relatively strong coastal and shelf break jets. The predicted currents were recently used by Zakardjian et al. (2001) to drive a stage-based life-history biological model. The main objective of their study is to determine the effects of water mass on the distribution and abundance of zooplanktic copepods in the region.
Sheng, Greatbatch and Wright (2001) recently proposed a semi-prognostic method to improve the utility of ocean models. The novel aspect of this method is that the model-computed currents are adjusted toward climatology, while leaving the model temperature and salinity equations unconstrained. Advantages of this approach are that the drift of the prognostic model results away from climatology is reduced, and the vertical mixing rates associated with convective mixing are more realistically represented. The semi-prognostic method is essentially a simplified optimal interpolation data assimilation scheme and is particularly useful for simulating the evolution of passive tracers in the ocean. The model results produced using this method show a significant improvement over those produced by either pure diagnostic or pure prognostic model runs.
Transport of carbon dioxide into the ocean is an important sink of anthropogenic carbon dioxide in the atmosphere. A reliable estimate of the pathways and fluxes of carbon dioxide in the North Atlantic, however, is not presently available. We collaborated with Drs. Dan Wright, Peter Jones and Kumiko Azetsu-Scott at Bedford Institute of Oceanography in the numerical study of major pathways of carbon dioxide in the Labrador Sea. In this study, we treated carbon dioxide as a passive tracer in the northwest Atlantic model discussed above, with idealized initial and boundary conditions. We integrated the tracer conservation equations with other model variables for five years. Tracers released in the upper water columns of the continental slope within the Labrador Sea drift southward with the Labrador Current. Before reaching the south tip of the Grand Banks, a significant amount of the tracers go eastward with the North Atlantic Current to the deep Atlantic waters. Others continue their journeys to the slope and deep waters off the Scotian Shelf and Gulf of Maine. The tracers released over the upper water columns of the deep waters of the Labrador Sea drift southward very slowly with a very small amount of the tracers moving equatorwards along the lower continental slope of the Northwest Atlantic.
In collaboration with Drs. Greatbatch, Harold Ritchie, Keith Thompson and Dan Wright, we submitted a research proposal to the Canada Foundation for Innovation (CFI) for the New Faculty Opportunities Award in 1999. We requested funding for a computer facility to enable computer intensive ocean/atmospheric modelling research at Dalhousie University. Our application was successful with total funding of $538,000 shared by the CFI (about 26%), Provincial Government of Nova Scotia (26%), Silicon Graphics (SGI, 41%, in-kind), and the Canadian Institute of Climate Studies (5%). The computer facility, which consists of an Origin 2000 rack-mounted server with 12 processors, has been fully operational since February, 2000.
a. Dr. Liang Wang was recruited in September 1999 as a Research Associate to work on the numerical study of passive tracers in the northwest Atlantic. Liang's background is in near-shore dynamics and sediment transport. He worked very closely with myself and Dr. Dan Wright of BIO in implementing a flux-limiter scheme in CANDIE to eliminate numerical noise associated with the advection terms.
b. Hualin Wong was recruited as a Research Assistant in August 2000 to work on the research project left by Liang. She also helped us design and maintain a very informative website for CANDIE (www.phys.ocean.dal.ca/programs/CANDIE).
c. Dr. Sheng Zhang was hired by Dr. Greatbatch and myself as a Research Associate to work on the sea ice modelling.
d. Mike Casey was recruited by Dr. Greatbatch and myself as the computer support for the chair program. Mike is responsible for our SGI computers and provides general computer support to our group.
a. Close collaboration with the senior chair Dr. Greatbatch in many research areas including the development of new monthly climatology (Geshelin et al., 2000), the semi-prognostic method (Sheng et al., 2001) and the numerical study of seasonal circulation in the northwest Atlantic.
b. Collaboration with Drs. Wright, Jones and Azetsu-Scott at BIO in the numerical study of the passive tracers in the Labrador Sea.
c. Continuous collaboration and coordination with Drs. Thompson and Bobanovic in the development of prototype operational forecast systems.
d. Interaction with Drs. Taggart and Reiss (Reiss, et al., 2000) on examining the implications of baroclinic circulation over Western Bank on the Scotian Shelf for larval fish transport and retention.
e. Interaction with Drs. Runge and Zakardjian of Institut des Sciences de la Mer de Rimouski on the numerical simulation of life history of the copepod over the Gulf of St. Lawrence and Scotian Shelf (Zkardjian et al., 2001).
This page last updated November 1, 2001.