Abstract

Pacific coastal North America typically benefits from seasonal upwelling during late spring and summer. The upwelled nutrients are critical to the survival and reproductive health of photosynthetic phytoplankton and hence the entire coastal ecosystem. Hence monitoring the timing and intensity of coastal upwelling is critical to environmental managers of these ecosystems. NOAA’s Pacific Fisheries Environmental Laboratory (PFEL) has produced the only routine upwelling index, derived from FNMOC sea surface pressure fields using an estimation of offshore Ekman transport driven by geostrophic wind stress. The Global Ocean Data Assimilation System (GODAS), with 1? x 1? spatial resolution and pentad temporal resolution of oceanographic properties since 1979, has the potential to monitor coastal upwelling in near real time. Vertical velocity data was chosen as a proxy for upwelling and computed at 15 standard coastal North American locations.

To assess the skill in monitoring the upwelling, GODAS-derived upwelling was compared with pentad averages of 6-hourly PFEL upwelling indices. Spatial correlation is encouraging, with correlation above 0.7 between 54N and 30N. Correlation diminishes north of 54N and south of 30N. A cumulative upwelling index (CUI) was also computed by annually integrating both PFEL and GODAS upwelling indices between the climatological onset on the upwelling season and the pentad date of maximum seasonal upwelling. The CUI captures the importance of both the timing of onset of the upwelling season in addition to the seasonal intensity. In an interannual basis, GODAS simulates anomalously weak and strong upwelling years well, and compares favorably with PFEL representations of upwelling variability. Potential exists to further develop an upwelling monitoring application of GODAS to be used in tandem with PFEL products. The ability to monitor upwelling in near-real time and potentially forecast the onset and intensity of the upwelling season can deliver large benefits for coastal ecosystem and fishery management.

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