RPS MetOcean maintain a number of gridded wind databases, which it uses for wave and hydrodymanic modelling. These are obtained from various Global Climate Meteorological Models (GCM) from various meteorological agencies.
Multiple databases are stored by RPS MetOcean as they vary both in temporal and spacial resolutions. Both the resolution of the meteorological model and the resolution stored within MetOcean vary, and this influences the reliablity of the data.
Below animation of model wind vectors of surface winds under TC Vance in 1999
Gridded Wind Databases
Since the mid 1970's global meteorological models have been run on computers
by a number of meteorological agencies for weather forecasting, one of
the parameters analysised and forecast is wind direction and speed.
Initially, the resolution of these GCM models were coarse at about 2°X2° (222km X 222km) but as computer power increased the resolution has become finer. Similarly the transmission and storage of the results was 2.5°X2.5° but as disk space has increased this reduced to 1°X1° in the late 1990's and to 0.5°X0.5° in recent times.
The input data to these models are observations from ships and meteorological island and land stations. These data were smoothed and contoured onto the analysis grid using various techniques, but were very susceptilble to observational and transmission error. Over time, the input of these observations into the analysis grid has became more sophisticated and provides reasonably reliable results since about 1992.
The source of the input data into the GCM's has also improved over time with the introduction of geostationary meteorological satellites in the 1980's and with the increase of remote sensing satellites in the 1990's. A major improvement was the Quikscat satellite in 1999, which provided twice-daily winds at 25km X25km resolution over the whole globe.
The gridded winds are stored over the complete globe at regular intervals typically 3 to 12 hourly.
Databases Stored by MetOcean
The source, domain, temporal and special resolutions and the period of record of the stored data within each wind database is shown in the following table:
|MetOcean Name of Gridded Wind||Domain||The Interval||Resolution||Period Available||Agency|
|No Gaps||65°E to 185°E
10°S to 67.5°S
|12 hourly||2.5°X2.5°||1980 to 1989||Us Navy|
|NMC||Global||12 hourly||2.5°X2.5°||1980 to 1989||US National Meteorlogical Centre|
|ncep||Global||6 hourly||1.0°X1.0°||2000 & ongoing||National Centres
|GFS||Global||1.0°X1.0°||November 2003 & ongoing||National Centres
|NRAW||Global||6 hourly||~1.87°X1.875°||1948 & ongoing||NCAR/NCEP|
Advantages of Various Database
NMC, NCEP and GFS
Generally the finer resolution the model the better the results. However, the meteorological models providing the NMC, NCEP and GFS gridded winds, change both in physics and in resolution over the years. Therefore, making comparisons over long periods of time is difficult and calibration based on the current model will not provide useful comparisons for modelled results from previous years.
The NRAW meteorological model was produced in response to the global
warming climate debate of the early 1990's, hence the coarse resolution.
The analysis and forecast model for all years are all based on the 1995
version of the one model, NCEP's Meduim Range Forecast (MRF) model.
This allows calibration based on modelled results to recent measurements to be applied to modelled results from previous years.
The major disadvantage is that the model is twice as coarse as the actual 1995 NCEP model.
Limitations of Winds and Editing
The storage and model resolution may have a major inpact for smaller
scale features, such as within the Bass Strait,.and provide overland
winds which tend to be much lighter, than overwater conditions.
The temporal and spacial resultion may not well represent seabreeze components
of the winds. The model and the storage resolutions of these GCM meteorological
models will not account for mesoscale features such as tropical cycones,
coastal lows, or convective features like squalls.
These features can be editted into the gridded winds by MetOcean, but this can be very time consuming.