Observations of circulation and related physical variables have been collected in Bahia Concepcion, on the Gulf of California side of the Baja California peninsula in Mexico. The first goal of the original study was to describe through observations how rotation affects the wind-driven circulation in a relatively deep, well-mixed, semi-enclosed bay. We are in the process of submitting those results for publication. The period of observations, originally planned to last only through the well-mixed winter season, was extended to the entire year, including the highly stratified summer season. The extended data set gives us the opportunity to describe the physics of the bay when the water column is stratified. This study focuses on three separate time scales: the seasonal cycle associated with the onset and demise of stratification, the internal tides, and the barotropic and baroclinic seiches. The second goal of the original study was to develop an analytical model to represent the circulation driven by tides and the effects of friction and rotation on the estuarine flow. Those tasks are now complete. Motivated by the results of the winter observations we propose here to develop analytical models of three-dimensional time-dependent wind-driven flow, including the effect of advection, and to extend the tidal modeling effort to include stratified basins.
Broader Impacts The ecological and societal importance of small coastal basins (bays, estuaries, lagoons) is out of proportion with their size. Among many other important ecological functions, lagoons and estuaries serve as way stations for migrating birds, as nurseries for an immense variety of fauna and flora and as mating and calving grounds for marine mammals such as the Pacific gray whale. At the same time these water bodies have been deeply impacted by anthropogenic activities. Many, if not all, are used as pathways through which sewage and contaminated waters are introduced into the ocean. In the past three years we have developed contacts with and given talks to engineering consultants and lay groups who are stewards of several lagoons in San Diego county. We plan to further develop these associations by providing free advice and consultation. By way of mitigation, The So. Cal. Edison company is undertaking an eighty million dollar restoration of San Dieguito Lagoon, north of San Diego. Here we propose to work with Coastal Environments, the consultancy charged with the scientific management of the project at the same time as we advise the San Dieguito Lagoon conservancy and other advocate groups. This project will allow us to participate in summer hands-on activities with high school students, and continue our outreach efforts with Florida elementary schools. In addition, this study represents a collaboration between scientists from the USA, including a minority representative, and Mexican scientists. The study will continue to enhance the participation of minority groups in science. It will train one graduate student and one Post-Doc and expose many others, including minority undergraduates, to state-of-the-art data collection, analysis and the application of numerical models. It will facilitate international cooperation and capacity building in Mexico and will also greatly enhance the courses taught by the PIs at graduate and undergraduate levels.
Award Number: 0726673 The health of coastal wetlands and embayments and their ability to function, in an ecological sense, depends on the rate at which water is exchanged between the basin and the adjacent ocean. That exchange is driven by physical processes: a combination of winds, tides and buoyancy forcing. Processes responsible for the wind-driven circulation in shallow, well-mixed basins, when the rotation of the earth can be neglected, are well-understood. It is also clear that the rotation of the earth has to be included in models of circulation in semi-enclosed seas, some of which are not much larger than the largest estuaries. This project was undertaken to describe how the rotation of the earth affects the character and complexity of circulation and fluid parcel trajectories, and determine what are the consequences for mixing and residence times. Observations of circulation and related physical variables were collected, as part of an international collaboration, in Bahia Concepcion, on the Gulf of California side of the Baja California peninsula in Mexico over a year-long period. The weather in this area is arid, there is very little precipitation and the winds blow in strength and persistently for extended periods. In particular Bahia Concepcion, the site of the observations, is exposed to strong winds aligned with the axis of the bay during the winter, when it is well-mixed, and the effect of the earths rotation is predicted to be significant. The central conclusion reached, after the observations were synthesized, is that the observed wind-driven circulation conforms qualitatively to the linear theory when the effect of the earths rotation is strong. Near the closed end of the basin the downwind flow is asymmetric, stronger in downwind direction on the right of an observer looking toward the closed end, with a return flow concentrated at depth and to the left of the observer. At the same time the lateral flow carries surface water to the right of the wind. At depth the lateral flow is in the opposite direction, driven by the lateral surface slope that balances the vertically integrated axial transport. The existence of this cyclonic gyre circulation was not known before this project, and will have significant impact on plans to manage this or similar Bays or Estuaries.
