This project will conduct a number of theoretical and numerical analyses of coastal and estuarine circulation focused on the mechanical energy budget. Mechanical energy (potential and kinetic) forms a powerful conceptual integrating tool between atmospheric, tidal, and river forcing of coastal flows, and the resulting vertical fluxes (both by overturning circulation and by turbulent mixing). However, our current understanding of the functioning of the energy budget is severely limited in coastal and estuarine flows by the combined effects of irregular domains, open boundaries, and highly variable forcing (and hence the lack of a steady state). The work will build on the PI's recent work on energy budgets in estuaries and on the Washington and Oregon continental shelf. This will lead to a greatly improved theoretical understanding of how coastal upwelling and the estuarine exchange flow work, and how sensitive they may be to changes in forcing conditions. Simulations will be done in both idealized domains and for realistic hindcasts of the WA/OR shelf including the Columbia River and Puget Sound.
Broader Impacts: The results of this work will be of benefit to the coastal and estuarine physics community by providing (i) a better theoretical understanding of energy budgets, and (ii) improved numerical tools to use with ROMS for energy analysis. The research will also increase our understanding of coastal upwelling, and of the linkages between shelf and estuarine systems, and hence the ecosystems which rely on these. This work will train a new graduate student in coastal and estuarine physical oceanography. It will support computational infrastructure that is used by many students at the UW School of Oceanography as a critical aspect of their research. It will also support a 5-week summer school.
The objectives of this project were to use an energy budget to better understand the timescale of coastal upwelling, the estuarine adjustment time, and the estuarine residence time. All three involve energy sources and sinks for the available potential energy (APE) pool, and the KE pool for the coastal case. In the course of conducting the research it became apparent that standard methods for calculating the estuarine exchange flow were inadequate to characterize estuarine timescales. We were able to solve this problem, and that solution method was a key contribution of the work. We also made progress in quantifying the contribution of remotely-generated internal waves to the energy budget on the continental shelf. Finally we succeeded in developing an exact method for calculating energy budgets in regional model simulations. Below are some details: Support from this grant allowed us to develop a technique for calculating momentum dynamics averaged over inflowing and outflowing volumes of an estuarine exchange flow. The subtidal exchange flow momentum balance in the Strait of Juan de Fuca can have local pressure gradient reversals due to tidal energy gradients, but when averaged correctly it is still controlled by the balance between bottom friction and a suitably redefined pressure gradient (Martin and MacCready 2011). We developed a theory for calculating the estuarine exchange flow using isohaline coordinates. The exchange flow quantified using isohaline coordinates has been termed the "Total Exchange Flow" (TEF) and has been shown to be a superior means of quantifying estuarine tidally-averaged transport and stratification (MacCready 2011, Sutherland et al. 2011). We analyzed our numerical simulations for barotropic-to-baroclinic tidal energy conversion, and compared to observations. Internal waves on the shelf in our model are too weak and come from the wrong direction, compared to observations. We believe this is because of the lack of offshore internal wave energy sources. In the model there is only local energy conversion. (Alford et al. 2012). This highlights the need for better characterization of the internal wave field impinging on coastal regions. Finally, we developed an exact energy budget for simulations done using the community ROMS (Regional Ocean Modeling System) modeling framework. Subawards to this grant supported the summer school taught by PI MacCready and Rocky Geyer (WHOI) at the UW Friday Harbor Labs in 2009 and 2012. We trained a total of 28 grad students from around the world. This award supported the writing of three review articles: (MacCready and Geyer 2010 Ann. Rev. Mar. Sci.; MacCready and Banas 2012 Estuary Treatise chapter; and Geyer and MacCready 2014 Ann. Rev. Fluid. Mech.) which included results from this grant. This grant supported a graduate student, Jamie Shutta. She successfully defended her Masters degree in March 2013 and is pursuing a career in K-12 education.
