Our group has a GLOBEC funded project to develop a series of nested ocean models culminating in a fine scale model of the Coastal Gulf of Alaska (CGOA).
Our primary interests are to determine the source of nutrients to the CGOA, and to compare our results for this downwelling system with those for the upwelling California Current system also being studied under GLOBEC. By doing this, we hope to explore the mechanisms by which interannual/interdecadal variability of physical fields affect zooplankton species and the feeding of juvenile salmon in the CGOA.
The model we are using is the Regional Ocean Modeling System (ROMS), version 2.0. We are currently running the model with several grids at differing resolutions, using the larger domains to provide boudary conditions for the smaller ones. The grids in order of increasing resolution are the Northern Pacific (NPac) grid, the Northest Pacific (NEP) grid, and the Coastal Gulf of Alaska (CGOA) grid. Also included in the nested set, but not used at PMEL specifically, are grids of the California Currrent (CCS), Bering Sea, and Prince William Sound.
This version of ROMS runs in parallel machines on distributed memory supercomputers. Our NEP and CGOA runs have been performed on FSL's supercomputer cluster of Intel Pentium nodes running Linux. This project also has access to time on the National Center for Atmospheric Research (NCAR) supercomputers, where the NPac runs were performed.
The models are forced with a variety of environmental data. The bulk flux algorithms are used to calculate wind stress and heat flux from atmospheric data. To improve results in the Gulf of Alaska, we use the results of a nested atmospheric model (MM5, Nick Bond and Rick Steed) when they are available. Other forcing include river runoff, a linesource of freshwater input along the Alaskan coast (NEP and CGOA), and 8 tidal components (CGOA, only).
To investigate biological production in the Gulf of Alaska, a Nutrient-Phytoplankton-Zooplankton (NPZ) model is embedded within the physical circulation model. Biology and physics are run concurrently (rather than using stored physical output fields as originally planned) so the impact of tidal mixing in the CGOA region can be fully simulated. Iron is used to differentiate ecosystems in the near-coastal (shelf and shelf break) and oceanic areas. Circulation and prey fields produced in this manner will eventually be used as input to an Individual Based Model (IBM) of juvenile salmon. Lagrangian floats tracks output by ROMS are also used to investigate nutrient pathways and salmon food availability.
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