Model Descriptions

CIOFS

The Cook Inlet Operational Forecast System (CIOFS) [NOAA [NOA19], Zhang [Zha19]] is focused on simulating the coastal oceanography of Cook Inlet in Alaska, based on the Regional Ocean Modeling System (ROMS) [Shchepetkin and McWilliams [SM05], McWilliams [McW09]]. The model domain extends from the offshore waters of the inlet to the inner estuaries and navigational channels (Fig. 1). The horizontal grid has 1,132 by 777 grid points, with spacing ranging from 10 meters in the estuaries to 3.5 kilometers in the deeper offshore waters. Vertically, the model uses 30 sigma layers that follow the bathymetric terrain. Bathymetry is based on the best available soundings, shoreline, and digital elevation data in order to accurately represent the complex inlet geometry and support wetting/drying processes.

Fig. 1 CIOFS domain with bathymetry.

The 20-year hindcast (1999–2018) product with hourly 3D hydrographic fields was produced by Axiom Data Science. For surface forcing, CIOFS primarily uses wind, temperature, and humidity fields from ECMWF Reanalysis v5 (ERA5) [HBB+20]. Lateral ocean boundary conditions including temperature, salinity, and sub-tidal water levels come from HYCOM Global Ocean Forecasting System (GOFS) 3.1 Reanalysis [NavalRLaboratory21]. Tidal forcing at the open boundary comes from the NOS CO-OPS version of CIOFS [NOAA [NOA19]; Zhang [Zha19]] which is derived from the ADCIRC tidal database [ADCd.]. River inputs use real-time discharge observations from 12 major rivers supplied by the USGS [USGS16].

The CIOFS hindcast simulations were performed using the Intel Fortran Compiler and Intel MPI (provided in Intel oneAPI base toolkit and HPC toolkit, version 2023) for parallelization on a local cluster consisting of 9 nodes. Each node contained 40 Intel Xeon Gold 6148 (Skylake) CPU cores, allowing for a total of 360 cores. Nodes were connected via QDR InfiniBand fabric. A single 3 hour simulation required approximately 5 minutes utilizing the full 360-core cluster. This allowed the 24-year hindcast spanning 1999-2022 to complete in approximately 7 months. This performance demonstrates efficient scaling to 360 cores, enabling the high resolution simulations required for this project to feasibly execute within a reasonable timeframe. The Intel compiler and MPI implementation tailored for the Xeon architecture was critical in maximizing utilization of the available compute capability.

See more details about the open boundary forcing files in Open Boundary Forcing and Initial Conditions and river forcing files in Details about river forcing files and Make monthly river forcing files for 1998–2022. The landing pages in the AOOS portal are available for the CIOFS hindcast and for the CIOFS forecast.

NWGOA

The NWGOA model Danielson et al. [DHH+20a] is a high-resolution regional ocean model focused on the northwest Gulf of Alaska, including Cook Inlet, Shelikof Strait, Prince William Sound, and Kodiak Island (Fig. 2). It uses the Regional Ocean Modeling System (ROMS) and has a horizontal resolution of approximately 1.5 km with 50 vertical layers. The model domain extends 1,100 km in the east-west direction and 550 km in the north-south direction, capturing important freshwater source regions like the Copper River delta and Prince William Sound.

Fig. 2 NWGOA domain with bathymetry.

It is one-way nested within a larger 10 km Northeast Pacific (NEP) model that provides oceanic boundary conditions. Atmospheric forcing comes from the MERRA global reanalysis product [RSG+11]. Tides are included based on the global TPXO tidal inversion [EE02]. A high-resolution gridded terrestrial discharge model was used to better represent freshwater inputs from rivers and coastal runoff. The model uses an updated bathymetric grid based on the 1 km Alaska Region Digital Elevation Model (ARDEM) and includes a sea ice model [Danielson et al. [DCH+11]; Danielson et al. [DDJ+15]]. It was integrated from 1999 to 2008 to overlap with available observations.

The landing page in the AOOS portal is avaiable for the NWGOA model.