Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 1999. / Includes bibliographical references (leaves 235-243). / A detailed examination of the development of a deep convection event observed in the Greenland Sea in 1988-89 is carried out through a combination of modeling, scale estimates, and data analysis. We develop a prognostic one-dimensional mixed layer model which is coupled to a thermodynamic ice model. Our model contains a representation of the lowest order boundary layer dynamics and adjustable coupling strengths between the mixed layer, ice, and atmosphere. We find that the model evolution is not very sensitive to the strength of the coupling between the ice and the mixed layer sufficiently far away from the limits of zero and infinite coupling; we interpret this result in physical terms. Further, we derive an analytical expression which provides a scale estimate of the rate of salinification of the mixed layer during the ice-covered preconditioning period as a function of the rate of ice advection. / by Jay Alan Austin. / Ph.D.
| Identifer | oai:union.ndltd.org:MIT/oai:dspace.mit.edu:1721.1/58538 |
| Date | January 1999 |
| Creators | Austin, Jay Alan |
| Contributors | Steven J. Lentz.We also derive an estimate for the rate of the mixed layer deepening which includes ice effects. Based on these scale estimates and model simulations, we confirm that brine rejection and advection of ice out of the convection area were essential ingredients during the preconditioning process. We also demonstrate that an observed rise in the air temperature starting in late December 1988 followed by a period of moderately cold ~ -10*C temperatures was key to the development of the observed convection event. Finally, we show that haline driven deep convection underneath an ice cover is possible, but unlikely to occur in the Greenland Sea. On the basis of these results, we develop a coherent picture of the evolution of the convection process which is more detailed than that presented in any previous work. We also comment on the likelihood that deep convection occurred in the Greenland Sea in the past two decades from an examination of historical data, and relate these findings to what is known about the inter-annual variability of convective activity in the Greenland Sea.Data from the Coastal Ocean Processes Inner Shelf Study are analyzed to determine atmospheric forcing characteristics and the heat balance of the inner shelf, and are used as motivation for a numerical study of inner shelf circulation during upwelling and downwelling. Variation in meteorological forcing on the North Carolina Inner shelf is shown to be dominated by synoptic weather systems. The structure of cold fronts, which are the dominant synoptic feature, and the local meteorological conditions they produce result in a strong correlation between the surface heat flux and the wind orientation. This has implications for the heat balance of the inner shelf, which is considered next. During stratified conditions (observed during August 1994), cross-shelf heat fluxes due to Ekman dynamics dominate variation in heat content of the inner shelf, while during weakly-stratified conditions (observed during October 1994), the surface heat flux dominated variation in heat content. Both processes are correlated with the alongshelf wind, implying that the heat balance of the inner shelf can be modeled largely in terms of the alongshelf wind. The dominance of cross-shelf processes during stratified conditions motivated numerical studies of upwelling and downwelling. It was found that the feedback between mixing and stratification played a role in determining the strength of the circulation on the inner shelf, which differed between upwelling and downwelling. During upwelling, dense water is brought onto the inner shelf from below the pycnocline, producing vertical stratification, lowering eddy viscosities, and enhancing the inner shelf circulation. In contrast, during downwelling, circulation was weakened by the presence of stratification. These circulation patterns are discussed in the context of coastal observations, and the implications for cross-shelf transport and exchange processes are considered., Woods Hole Oceanographic Institution., Joint Program in Physical Oceanography, Woods Hole Oceanographic Institution, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| Publisher | Massachusetts Institute of Technology |
| Source Sets | M.I.T. Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 243 leaves, application/pdf |
| Rights | M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission., http://dspace.mit.edu/handle/1721.1/7582 |
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