This research includes both methodological development and scientific analyses of coastal currents and their interactions with the offshore circulation in both eastern and western boundary currents (EBCs and WBCs). We are developing methods to extend the altimeter sea surface height (SSH) fields into the region within 50 km of the coast; and to address the over-riding scientific question in each system, --To what extent does the offshore circulation affect the coastal circulation?" We will use: altimeter SSH, scatterometer winds, IR and microwave SST, and surface Chlorophyll-a concentrations to characterize the large-scale and regional forcing of, and response within, the coastal regions. High-resolution numerical models will extend the satellite analyses beneath the surface and quantify the dynamical relationships governing the circulation.
Three coastal regions are compared: the California Current System (CCS) off the western U.S.; the Peru-Chile Current System (PCCS) off western South America; and the Southwestern Atlantic Current System (SWACS) off eastern South America. Including the SWACS, with its wide coast and strong western boundary currents, will allow us to develop and test coastal altimetric techniques in regions with both narrow and wide shelves, and with both strong (WBCs) and weak (EBCs) offshore currents.
We are initially using the 3-year period from Autumn 2002-2005, when 4 altimeters were operating and ancillary satellite data are available for winds, SST and CHL. This period provides the best coverage and allows us to compare analyses using the full data set to analyses of subsets of the data that match the sampling during other periods. Analyses of the complete 15+ year altimeter data record will encompass strong El Niño-La Niña signals and reversals in the signs of the PDO, NAO and SAO.
This research builds on results from our present OSTM work, which examines distant and local forcing for the large-scale eastern boundary currents, but does not include the more coastal areas or the South American WBC (SWACS). These coastal areas include some of the oceans' most productive ecosystems and fisheries, with important economic consequences when those systems change. Thus, the research will accelerate the realization of societal benefits in the form of increased understanding of circulation and changes in the coastal ocean, where human activities strongly impact, and are impacted by, ocean conditions. By combining satellite data and models, we will increase our ability to interpret both satellite and model fields, eventually leading to better interpretations of coastal model predictions, nested within basin-scale models of climate change. This research will also help prepare for coastal applications of future high-resolution altimeters, such as NASA's Surface Water Ocean Topography (SWOT) mission.
Interactions Between Coastal and Offshore Circulation