## 4 Discussion
### Comparison of HY-2C and CFOSAT Inversion Data with ERA5  
This study assessed the accuracy of satellite-retrieved sea surface wind speed data by comparing CFOSAT and HY-2C satellite-retrieved wind data with ERA5 reanalysis wind data for the same period as in Section 3.3.1. By subtracting the satellite-retrieved wind speed values at the corresponding times from the ERA5 reanalysis wind speed values, the results shown in Figure 12 were obtained.  
Figure 12 shows that CFOSAT's retrieved sea surface wind speed during the low wind speed period was slightly lower than the ERA5 reanalysis data in the northern Yellow Sea, while it was somewhat higher in the southern Yellow Sea. Near 34\({}^{\circ}\)N, the wind speeds of both datasets exhibited a similar performance. Similar trends were also evident in HY-2C's retrieved sea surface wind speeds, which were lower than ERA5 reanalysis data in the northern Yellow Sea and slightly higher in the southern Yellow Sea, with a relatively large deviation of up to 8 m/s in the south of the region.  
Figure 10: Comparison of wind energy density between HY-2C, CFOSAT satellite inversion 10 m wind field, and WRF simulation at each height.  
During the moderate wind speed period, CFOSAT's retrieved sea surface wind speed was slightly higher than ERA5 reanalysis data in the northern Yellow Sea and somewhat lower in the southern Yellow Sea. Near 33.5\({}^{\circ}\)N, both datasets showed relatively similar wind speed patterns. Compared to CFOSAT, HY-2C's retrieved sea surface wind speed also exhibited identical results to ERA5 reanalysis data during the moderate wind speed period. However, HY-2C had slightly larger errors relative to ERA5 reanalysis data.  
In the high wind speed period, both satellite datasets generally overestimated the wind speed values over most oceanic regions, with some overestimation observed in the northwestern Yellow Sea. Overall, CFOSAT and HY-2C satellite-retrieved sea surface wind speed data showed significant deviations when compared to ERA5 reanalysis data, with higher discrepancies than those observed in comparison with WRF simulation results.  
Figure 11: Research flow chart.  
Figure 12: Comparison of HY-2C and CFOSAT inversion data with RA5 reanalysis sea surface wind speeds. The values in the figure represent the difference between the satellite-retrieved wind speeds and ERA5 reanalysis wind speeds. (**a1**) Represents the difference between CFOSAT’s retrieved sea surface wind speed and ERA5 reanalysis wind speed during low wind speeds, (**a2**) represents the difference during moderate wind speeds, and (**a3**) represents the difference during high wind speeds. Similarly, (**b1–b3**) represent the differences for HY-2C’s retrieved sea surface wind speed compared to ERA5 reanalysis wind speed during low, moderate, and high wind speed conditions, respectively.  
In conclusion, careful analysis and evaluation of error patterns in different wind speed periods and regions are necessary to ensure the accuracy and reliability of satellite-retrieved sea surface wind speed data. Additionally, when using satellite-retrieved data, consideration should be given to potential error sources arising from different satellite instruments and data processing algorithms to enhance data quality and credibility further.