Work on this collaborative project with the Massachusetts Institute of Technology and Harvard University focused on the study of the physics and statistics of sea level change over the last two decades at both regional and global levels. Sea level rise can have enormous socio-economic consequences for the millions of people living in the coastal zones of the global ocean. Understanding what governs sea level behavior, at time scale from days to decades, is thus an endeavor of extreme relevance for society at large. Our project has addressed this challenge by making synergistic use of most available satellite and in situ data, advanced ocean models, and powerful estimation methods. All together, these tools allow for optimal estimation of sea level fluctuations and their causes, along with insights on shortcomings of both data and models and potential ways for their future improvement.

Our analyses show that surface winds, heat fluxes and atmospheric pressure can all drive substantial sea level fluctuations at periods of months to years. Coastal regions can exhibit decoupled behavior from the adjacent deep oceans, and some can be affected by short scale (“eddy”) variability that is intrinsically oceanic and not easily determined from atmospheric forcing alone. In addition, atmospheric driving mechanisms can act locally and remotely, with locally forced anomalies in temperature and salinity being advected by ocean currents or propagated through available ocean waves modes and affecting sea level elsewhere. Apart from advection, diffusion mechanisms can also be important locally. 

Although thermal expansion and contraction effects, which do not imply a change in mass, can be the primary cause of low-frequency sea level, particularly at lower latitudes, changes in bottom pressure, representing integrated mass anomalies over the water column, cannot be neglected especially at high latitudes and in shallow depths. Effects of salinity also contribute in regions like the Arctic and the North Atlantic. Accounting for deep temperature and salinity variability (below depths of 2000 m, and thus not easily observed) is found to be important as well for interpretation of the surface height signals.

All in all, findings of the project point to a complex mixture of atmospheric and oceanic processes as controlling factors for both global and regional sea level change. As a result, most accurate knowledge of all these processes, from forcing winds to diffusion by turbulent eddies, is needed for best sea level modeling and forecasting capabilities. Our analysis show that inclusion of missing physics, such as response to long-period tidal loading, effects of self-gravitation and crustal loading, or forcing by bottom geothermal heating, and more comprehensive data sets, are all needed for improving sea level estimates and advancing present understanding of the relevant dynamics. 

Last Modified: 06/23/2015
Modified by: Rui M Ponte