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WIND MODELS

Introduction

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 for Environmental
Prediction
GFS Global   1.0°X1.0° November 2003 & ongoing National Centres for Environmental
Prediction
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.

NRAW

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.