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Evaluation of ECMWF and NCEP Reanalysis Wind Fields for Long-Term Historical Analysis and Ocean Wave Modelling in West Africa

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Abstract

Ocean wind fields form a significant input to ocean wave models. This study evaluates the accuracy of two major reanalysis wind fields: NCEP-NCAR reanalysis-II (NNR-II) and ECMWF ERA5 wind datasets in the marine domain of West Africa. The objective is to identify the reanalysis data that best represents the wind regimes of the sub-region for use in climate studies and ocean wave modelling. The reanalysis datasets were validated against in situ measurements from PIRATA meteorological buoys in the region. Both reanalysis datasets indicate good agreement with in situ measurements and capture the variability in the wind fields. However, ERA5 wind fields outperform the NNR-II wind fields and better represents the variability in wind fields in the region. They display higher correlation coefficients and R-squared values as well as lower bias and RMSE values for all wind components at all PIRATA buoy locations. Correlation coefficients of 0.92, 0.87, 0.94, and 0.98; R-squared values of 0.83, 0.76, 0.89, and 0.96; mean bias of −0.34±0.75 ms−1, 0.25±33.75°, 0.07   ±   0.86 ms−1, and −0.21±0.96 ms−1; and RMSE values of 0.82 ms−1, 33.75°, 0.87 ms−1, and 0.98 ms−1 were observed for ERA5 resolved wind speeds, wind directions, and zonal and meridional winds respectively. NNR-II also recorded correlation coefficients of 0.64, 0.7, 0.73, and 0.9; R-squared values of 0.19, 0.39, 0.32, and 0.79; mean bias of 0.12±1.77 ms−1, 8.91±53.43°, 0.55±2.09 ms−1, and −0.31±2.15 ms−1; and RMSE values of 1.77 ms−1, 54.17°, 2.16 ms−1, and 2.17 ms−1 for resolved wind speeds, wind directions, and zonal and meridional winds, respectively. NNR-II winds tend to highly overestimate zonal wind speeds and underestimate meridional wind speeds. Meridional winds are better predicted compared to zonal winds for both NNR-II and ERA5 winds. There was a general overestimation of lower wind speeds and underestimation of higher wind speeds on the part of both reanalysis datasets although this assertion varied with geographical location. To enhance the accuracy of resolved wind velocities and directions in the region, there is the need to improve the estimation of zonal winds in general by both NNR-II and ERA5 winds but with much efforts needed for NNR-II. In effect, ERA5 reanalysis winds better describe the wind regime of West Africa for climate studies and ocean wave modelling.

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Data Availability

In this paper, ECMWF ERA5 reanalysis wind data were obtained from https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-pressure-levels?tab=overview; NCEP reanalysis wind data were obtained from https://ftp.cdc.noaa.gov/Datasets/ncep.reanalysis2/gaussian_grid/; Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) meteorological buoy data were obtained from https://ftp1.ifremer.fr/Core/INSITU_GLO_NRT_OBSERVATIONS_013_030/history/mooring/.

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Acknowledgements

ECMWF ERA5 data was obtained from the Copernicus Climate Change Services (C3S) and NCEP Reanalysis 2 data was provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA. PIRATA in situ data was also obtained through the Copernicus Marine Environment Monitoring Service (CMEMS). Data analysis and figures were generated using Matlab®. Thanks to Prof. Ebenezer Nyadjro of Mississippi State University/NOAA Northern Gulf Institute for his useful comments. We also acknowledge Professor Michael J. McPhaden of the Pacific Marine Environmental Laboratory/NOAA, for his encouragement and helpful suggestions. We thank the anonymous reviewers whose comments helped improve the manuscript. This study is part of the PhD. thesis of Bennet Atsu Kwame Foli.

Funding

This study was supported by the Global Monitoring for Environment and Security and Africa (GMES & Africa) project at the University of Ghana. Partial financial support was provided by the Open Society Foundation (OSF) under the Enhancing Efficiency and Effectiveness – Climate Change and Sustainability Development (EEE-CCSD) project.

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Authors and Affiliations

  1. Department of Marine and Fisheries Sciences, College of Basic and Applied Sciences, University of Ghana, P. O. Box LG99, Legon, Ghana

    Bennet Atsu Kwame Foli, Kwasi Appeaning Addo & George Wiafe

  2. Global Monitoring for Environment and Security and Africa, College of Basic and Applied Sciences, University of Ghana, c/o P. O. Box LG99, Legon, Ghana

    Bennet Atsu Kwame Foli & George Wiafe

  3. Institute of Environment and Sanitation Studies, University of Ghana, Legon, Ghana

    Kwasi Appeaning Addo

  4. Department of Mathematics, University of Ghana, Legon, Ghana

    Joseph K. Ansong

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  1. Bennet Atsu Kwame Foli
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Correspondence to Bennet Atsu Kwame Foli.

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Foli, B.A.K., Appeaning Addo, K., Ansong, J.K. et al. Evaluation of ECMWF and NCEP Reanalysis Wind Fields for Long-Term Historical Analysis and Ocean Wave Modelling in West Africa. Remote Sens Earth Syst Sci 5, 26–45 (2022). https://doi.org/10.1007/s41976-021-00052-3

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