Definitions
Technical terms, mathematical symbols, and acronyms used throughout this documentation and in the dataset metadata.
Technical Terms
- Hindcast
- A historical simulation of ocean conditions using a numerical model driven by observed atmospheric forcing and tidal boundary conditions. Unlike a forecast (which predicts future conditions) or direct measurements, a hindcast reconstructs past conditions by running the model over a historical time period. The results represent modeled estimates of what conditions were, not direct observations.
- Sigma Layer
- A terrain-following vertical coordinate system where the water column is divided into layers that conform to both the seafloor and the time-varying sea surface. See Sigma Layers for details.
- Depth-Averaged
- A value computed by averaging a quantity across all vertical layers (sigma layers) at a given horizontal location and time. Produces a single representative value for the entire water column.
- Depth-Maximum
- The maximum value of a quantity across all vertical layers at a given horizontal location and time. Captures the peak value occurring anywhere in the water column.
- Free-Stream Velocity
- The undisturbed flow velocity that would exist in the absence of any energy extraction device. All values in this dataset represent free-stream conditions.
- Unstructured Grid
- A computational mesh composed of irregularly-shaped triangular elements. See Unstructured Grid for details.
Symbols
| Symbol |
Definition |
| U |
Current speed (velocity magnitude), m/s |
| \(\bar{U}\) |
Mean (time-averaged) current speed, m/s |
| u |
Eastward velocity component, m/s (positive toward true east) |
| v |
Northward velocity component, m/s (positive toward true north) |
| P |
Power density (kinetic energy flux per unit area), W/m² |
| \(\bar{P}\) |
Mean (time-averaged) power density, W/m² |
| \(\rho\) |
Seawater density, kg/m³ (nominal value: 1025 kg/m³) |
| h |
Bathymetry depth below NAVD88, m (positive downward) |
| \(\zeta\) |
Sea surface elevation relative to NAVD88, m (positive upward) |
| d |
Water depth (total water column height), m |
| R |
Grid resolution (average triangle edge length), m |
| T |
Time period (hindcast duration = 1 year) |
| t |
Time index |
| i |
Sigma layer index (1 to \(N_\sigma\)) |
| \(N_\sigma\) |
Number of sigma layers (= 10 in this dataset) |
| \(\sigma\) |
Sigma coordinate (terrain-following vertical coordinate) |
| \(P_{95}\) |
95th percentile operator |
Acronyms
| Acronym |
Definition |
| FVCOM |
Finite Volume Community Ocean Model |
| NAVD88 |
North American Vertical Datum of 1988 |
| MSL |
Mean Sea Level |
| IEC |
International Electrotechnical Commission |
| IEC 62600-201 |
International standard for tidal energy resource assessment and characterization |
| CF Conventions |
Climate and Forecast Conventions |
| PNNL |
Pacific Northwest National Laboratory |
| H2O |
Hydropower and Hydrokinetic Office |
| VAP |
Value-Added Product |