Exploring Estuarine Sea Level Fluctuations and Dynamics Using the Surface Water and Ocean Topography (SWOT) Mission: A Multi-System, Multi-Timescale Analysis

Principal Investigator: Sarah Giddings (Scripps Institution of Oceanography, UCSD)

Co-Investigator(s): Angelica Rodriguez

Collaborator(s): Salme Cook, Parker MacCready, Jeffrey Anderson

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Estuaries provide extensive ecosystem, economic, and human services. They have immense potential to aid coastal resilience, yet are simultaneously acutely sensitive to rising sea levels and climate-induced storm impacts. At the interface between ocean and land, estuarine processes and estuarine-ocean exchange link the upstream river to the coastline and open ocean. Estuarine dynamics are characterized by a variety of regimes based on the time scales of interest, estuarine geometry, river discharge, atmospheric forcing, as well as offshore oceanic conditions. Due to the complex, 3-D nature of estuarine circulation and mixing, it is difficult to obtain a full spatial dynamical picture through observations. Thus, in situ field deployments, airborne surveys, and shipboard transects, are often combined with regional numerical models. Sea level fluctuations over the expanse of estuarine systems are typically derived from sparse in situ pressure sensors or are model-based. The Surface Water and Ocean Topography (SWOT) mission, provides a novel data set to examine estuarine sea level fluctuations at scales previously unobtainable by space-based platforms and over the estuarine expanse. This novel data is providing a new means of studying estuary water level processes over a variety of time scales.

Our project is examining SWOT data collected over several estuaries that span a variety of dynamical regimes, scales, and forcing conditions: The Salish Sea, Willapa Bay, Grays Harbor, Arcata Bay, San Francisco Bay, San Diego Bay, and Delaware Bay. Leveraging existing numerical models and in situ observations, we are 1) assessing the accuracy of tidal corrections, as well as 2) studying the dynamical features that SWOT observes. Tidal forcing, the ocean force driven by the gravitational pull of the sun and moon, is a leading order driver of estuarine circulation on hourly time scales. At time scales from days to months, we are exploring the propagation of oceanic sea level signals into the estuaries, including how changes in offshore sea levels caused by El Niño/La Niña events, offshore upwelling/downwelling, and storm surges impact water level within the estuaries. In doing so, we will track features seen in the data that can be further explored in space and time with the models which provide additional variables to assist in explaining the observed sea surface features. Through comparisons between systems, we will be able to characterize a comprehensive set of observed dynamic signals within the SWOT dataset, thus providing bounds on the utility of SWOT observations within U.S. West Coast estuarine environments and ultimately providing a better understanding of estuarine resiliency to sea level rise, variations in freshwater input, and storm surge inundation.