Liqun Jia, Shimei Wu, Bo Han, Shuqun Cai, Renhao Wu. Wave hindcast under tropical cyclone conditions in the South China Sea: sensitivity to wind fields[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2227-1
Citation:
Liqun Jia, Shimei Wu, Bo Han, Shuqun Cai, Renhao Wu. Wave hindcast under tropical cyclone conditions in the South China Sea: sensitivity to wind fields[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2227-1
Liqun Jia, Shimei Wu, Bo Han, Shuqun Cai, Renhao Wu. Wave hindcast under tropical cyclone conditions in the South China Sea: sensitivity to wind fields[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2227-1
Citation:
Liqun Jia, Shimei Wu, Bo Han, Shuqun Cai, Renhao Wu. Wave hindcast under tropical cyclone conditions in the South China Sea: sensitivity to wind fields[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2227-1
School of Atmospheric Sciences, Sun Yat-Sen University and Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519082, China
2.
State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
Funds:
The Major Projects of the National Natural Science Foundation of China under contract No. U21A6001; the Program of Marine Economy Development Special Fund under Department of Natural Resources of Guangdong Province under contract No. GDNRC [2022]18; the Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) under contract No. SML2021SP207; the State Key Laboratory of Tropical Oceanography, SCS Institute of Oceanology, Chinese Academy of Sciences under contract No. LTO2001.
Reliable wave information is critical for marine engineering. Numerical wave models are useful tools to obtain wave information with continuous spatiotemporal distributions. However, the accuracy of model results highly depends on the quality of wind forcing. In this study, we utilize observations from five buoys deployed in the northern South China Sea from August to September 2017. Notably, these buoys successfully recorded wind field and wave information during the passage of five tropical cyclones of different intensities without sustaining any damage. Based on these unique observations, we evaluated the quality of four widely used wind products, namely CFSv2, ERA5, CCMP, and ERAI. Our analysis showed that in the northern South China Sea, ERA5 performed best compared to buoy observations, especially in terms of maximum wind speed values at 10 m height (U10), extreme U10 occurrence time, and overall statistical indicators. CFSv2 tended to overestimate non-extreme U10 values. CCMP showed favorable statistical performance at only three of the five buoys, but underestimated extreme U10 values at all buoys. ERAI had the worst performance under both normal and tropical cyclone conditions. In terms of wave hindcast accuracy, ERA5 outperformed the other reanalysis products, with CFSv2 and CCMP following closely. ERAI showed poor performance especially in the upper significant wave heights. Furthermore, we found that the wave hindcasts did not improve with increasing spatiotemporal resolution, with spatial resolution up to 0.5°. These findings would help in improving wave hindcasts under extreme conditions.
Figure 1. The study area (black solid line), bathymetry (color fill), and tracks of five TCs during the study period. The magenta triangles represent buoy positions. TC: tropical cyclone.
Figure 2. Time series of U10 (wind speed at 10 m height, the left column, in units of m s-1), wind direction (right column, in units of ˚) between four wind data and corresponding buoy observations, with the time period from August 1 to September 30, 2017. The five periods of TC occurrences are marked with a semi-transparent background color. From left to right: TC Hato, TC Pakhar, TC Mawar, TC Guchol, TC Doksuri. U10: wind speeds at 10 m; TC: tropical cyclone; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 3. Taylor diagram of U10 comparison at five buoys. The five columns from left to right are five buoys B1-B5. The three rows from top to bottom are the entire period of this study (from August 1 to September 30, 2017), tropical cyclone-only period, and tropical cyclone-free period, respectively. The points A, B, C, D, O in the Taylor diagram represent CCMP, ERAI, ERA5, CFSv2, and buoy observations, respectively. U10: wind speeds at 10 m; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 4. Scatter diagram of U10 obtained from four wind data and buoy observations between August 1 and September 30, 2017. The five columns from left to right represent five buoys. The x-axis represents U10 selected from four wind products, the y-axis represents U10 from the buoy observations. The black lines represent for the perfect agreement between wind data and observations. The red lines and blue lines are fitted lines from different fitting formulas. The rectangular squares of different colors represent the number of scatters (multiples of 50). U10: wind speeds at 10 m; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 5. Magnitude of time-averaged wind speed in the study area. The four columns from left to right represent four wind data. The three rows from top to bottom represent the entire period, tropical cyclone-only period, and tropical cyclone-free period. The black dots are the buoy positions. CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 6. Contour distribution of the 99th percentile on wind speed during tropical TCs. The five rows from top to bottom are five tropical cyclone periods. The four columns are four snapshots during the TCs. The black lines are the TC tracks. The four colored contours represent four wind data. TC: tropical cyclone; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 7. Time series comparison of Hs (left column, in units of m) and wave direction (right column, in units of ˚) obtained from corresponding wave hindcast and buoy observations. The five periods of tropical cyclone occurrences are marked with a semi-transparent background color. Hs: significant wave height; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 8. Time series comparison of Tm01 (left column, in units of s) and RTP (right column, in units of s) obtained from corresponding wave hindcast and buoy observations. The five periods of tropical cyclone occurrences are marked with a semi-transparent background color. Tm01: mean absolute wave period; RTP: peak period of variance density spectrum; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 9. Taylor diagram of significant wave height comparison at five buoys. The five columns from left to right are five buoys B1-B5. The three rows from top to bottom are the entire period, tropical cyclone-only period, and tropical cyclone-free period. The points A, B, C, D, O in the Taylor diagram represent CCMP, ERAI, ERA5, CFSv2, and buoy observations, respectively. CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 10. Scatter plot of Hs obtained from wave hindcasts and buoy observations over the entire period. The five columns from left to right represent five buoys. The x-axis represents Hs selected from four wind products, the y-axis represents Hs from the buoy observations. The black lines represent perfect agreement between wind data and observations. The red and blue lines are fitted lines from different fitting formulas. The rectangular squares of different colors represent the number of scatters (multiples of 50). Hs: significant wave height; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 11. Magnitude of time-averaged Hs in the study area. The four columns from left to right represent four wind data. The three rows from top to bottom represent for entire period, tropical cyclone-only period, and tropical cyclone-free period. The black dots are the buoy positions. Hs: significant wave height; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 12. Contour distribution of the 99th percentile of significant wave heights during TCs. The five rows from top to bottom are five tropical cyclone periods. The four columns are four snapshots during the TCs. The black lines are the TC tracks. The four colored contours represent four wind data. TC: tropical cyclone; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 13. Waverose diagram of Hs and wave direction obtained from experiments with different resolutions. The five rows from top to bottom correspond to the original results, spatial resolution of 0.5˚, spatial resolution of 1.0˚, temporal resolution of 3 hours, and temporal resolution of 6 hours, respectively. The five columns from left to right are at buoys B1-B5. The three colors in each plot represent different ranges of Hs. Hs: significant wave height.
Figure 14. The same as Fig. 12. The contours represent the 99th percentile of significant wave height under different resolution experiments.
Figure 15. Scatter diagram of U10 obtained from four wind data and buoy observations in tropical cyclone-only period. U10: wind speeds at 10 m; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 16. Scatter diagram of U10 obtained from four wind data and buoy observations in tropical cyclone-free period. U10: wind speeds at 10 m; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 17. Scatter diagram of Hs obtained from wave hindcasts and buoy observations in tropical cyclone-only period. Hs: significant wave height; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
Figure 18. Scatter diagram of Hs obtained from four wave hindcasts and buoy observations in tropical cyclone-free period. Hs: significant wave height; CCMP: Cross-Calibrated Multiplatform; ERAI: ERA-Interim; ERA5: ECMWF Reanalysis v5; CFSv2: NCEP Climate Forecast System Version 2.
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