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Ocean Surface Topography from Space
SCIENCE
Integrating altimetry and coastal ocean observing systems for coastal circulation applications at multiple temporal and spatial scales


Author:

John Wilkin - (Rutgers University, New Brunswick)

Co-Investigator/Institutional PI:
  Dr. Douglas Vandemark
(Rutgers University, New Brunswick)


Co-Investigator(s):
  Javier Zavala-Garay
(Rutgers University, New Brunswick)


Abstract:
This project will (i) pursue developments to integrate altimeter SSH data with coastal ocean models using advanced data assimilation, and (ii) jointly analyze altimetry, complementary satellite data, in situ observations from coastal observing networks, and data assimilative model experiments to study processes in the Gulf of Maine (GOM) and Mid-Atlantic Bight (MAB) across multiple temporal and spatial scales from the mean to the sub-mesoscale.

The project will address issues that confront coastal oceanographers and modelers who wish to make use of altimeter data in coastal and shelf seas to analyze and forecast coastal circulation.

The project team has developed an analysis system that combines Jason, Cryosat and AltiKa data derived using near-to-coast range corrections and re-tracking (coastal altimetry) with a high-resolution ocean circulation model (ROMS) using 4-D variational (4DVAR) methods for data assimilation, and 2-way nesting to locally achieve sub-km scale resolution. The system is implemented for the GOM and MAB where the MARACOOS and NERACOOS coastal observatories and the NSF Ocean Observatories Initiative Pioneer Coastal Array provide complementary data for skill assessment and further data assimilation (currents from HF-radar and moored current-meters; temperature/salinity data from moorings, profiling floats and gliders.)

With these modeling and observing instruments we will examine the error budget of altimetric coastal SSH and circulation estimates, beginning with Mean Sea Surface (MSS), Mean Dynamic Topography (MDT) and geoid in shelf seas, proceeding through geophysical corrections to altimeter range, to an analysis of effective resolution of models and altimetry.

Observing System Experiments will evaluate how resolution and accuracy of total water level above datum at the coast (a key factor in coastal inundation analysis) improves with increasing numbers of altimeters. Model twin experiments and nested models will explore how well data assimilation can exploit the sampling characteristics of future wide-swath altimeter missions to project information to unobserved space/time scales. Data from coastal observatories and the Pioneer Array will be used to examine how well data assimilative systems recover subsurface ocean temperature and salinity in coastal environments. With these full water column analyses of shelf seas we will explore a suite of physical oceanographic processes of particular interest in the GOM and MAB.

Specific detailed project goals are:

  1. Develop robust methods for reducing errors in geoid, MSS and MDT that impact near coastal total dynamic height, especially for altimeters (Cryosat, Sentinel-3, SWOT) whose ground-tracks do not coincide with the long-term reference missions
  2. Examine wavenumber spectra of along-track altimetry, HF-radar surface currents, and nested models to infer the noise/signal ratio and effective resolution of the respective data sources, spectral characteristics of sea level and velocity variance in shallow coastal seas, and convergence of model resolution
  3. Address regional physical oceanography questions regarding: the partition of inflow to the GOM between source waters on the shelf versus deeper slope and offshore waters that drive seasonal and inter-annual variability in GOM salinity and temperature; and, across-shelf fluxes at the MAB shelf-break that are mediated by frontal and eddy variability, boundary layer processes, and vertically sheared across-shelf flow in the presence of vertical tracer stratification.
  4. Assess the accuracy of multi-mission sea level and surface velocity data products (OSCAR/GlobCurrent) for coastal oceanographic applications on the NW Atlantic shelf, and globally. Lessons from our error budget analysis, MSS/MDT enhancement, time/space scale analysis, and data assimilation experiments will inform approaches to producing future skillful global coastal sea level and circulation products



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