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Using GlobWave data to validate regional wind and wave models

This case study, written by Laure Grignon, describes how HR Wallingford used GlobWave data to validate regional wind and wave models.

HR-Wallingford iconHR Wallingford

Introduction

HR Wallingford provides specialist research and consultancy studies, including offshore MetOcean and wave modelling studies to transform offshore waves and provide design conditions at coastal facilities. Their projects are located all over the world, often in places where no in-situ measurements are available. GlobWave has provided additional data to validate offshore conditions estimated from global and regional wind and wave models, representative of an average in space and time rather than an instantaneous measure of the wind or wave height.

Validating Global Waves model data offshore of Uruguay

GlobWave data have also been used to validate model data from the global NOAA WAVEWATCH III model offshore of Uruguay. The figure below shows time series of offshore significant wave height (SWH) from:

  • NOAA's WW3 (NWW3) model (1° by 1.25° resolution);
  • GlobWave data from a 0.5° by 0.5° box around the NWW3 point
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Figure 1: GlobWave (blue) vs NWW3 predicted significant wave heights (red) offshore Uruguay

This illustrates the limitation of the satellite track data when trying to validate a time series at a point location. Also, when choosing the size of the region from which the GlobWave data are to be extracted for comparison, there is a compromise between the availability and the relevance of the data.

However, as shown in the figure below, the GlobWave data give good information about the spatial variability across an area. The upper figure shows the location of the track relative to the coast and the available NWW3 grid points in the area. The lower figure shows the comparison as a function of distance from the coast, and shows good agreement between the model and the satellite data.

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Figures 2 & 3: GlobWave Track and NWW3 grid points (upper). GlobWave (blue) vs. NWW3 (red) predicted significant wave heights (lower)

Validating regional winds models in the Arabian / Persian Gulf

GlobWave wind data has been used to validate a Weather Research and Forecasting atmospheric model (WRF) built for the Arabian / Persian Gulf to downscale global atmospheric model data to a regional scale. Data was used from the Jason-1, Jason-2 and Envisat altimeters. Each satellite track takes of the order of seconds to cross a typical local model area, and a few minutes to cross a typical regional model area (such as the Arabian / Persian Gulf). As there may be several hours between available tracks over a region of interest, GlobWave data was used to capture the spatial, rather than the temporal variability. The spatial resolution of the satellite data is higher that both global models, typically 50 to 100 km and downscaled models, typically 5 – 10 km. The following figure shows a comparison of predicted wind speeds from WRF and ECMWF (European Centre for Medium range Weather Forecasting) against the GlobWave data for a track through the Arabian / Persian Gulf. This demonstrates both the improved spatial resolution of the satellite data and also its suitability for validating both the regional and global models.

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Figures 4 & 5: GlobWave vs Predicted wind speeds (upper) and satellite track (lower)

Conclusions

These studies have shown that GlobWave data can be used to validate regional downscaled atmospheric model wind (WRF) predictions and to validate global wave model data from NOAA and ECMWF.

Due to the success of these results, GlobWave data will continue to be used by HR Wallingford to calibrate and validate global and regional wind and wave models.