Fine-Scale Temporal Wind Variability in ERA5 and Its Implications for Wind Stress Calculation

High-frequency wind variability plays a critical role in understanding air–sea interactions. In this study, we evaluate the performance of ERA5 reanalysis in capturing fine-scale wind variability and its impact on wind stress estimates using half-hourly observations collected from a coastal island station. Spectral analysis shows that ERA5 significantly underestimates kinetic energy at subdaily frequencies. To quantify the consequences of this spectral deficiency, we calculate subdaily wind kinetic energy. ERA5 consistently shows lower subdaily energy compared to observations. Using both two wind stress bulk formulas, we further estimate the contribution of subdaily wind variability to daily wind stress. Our results show that subdaily fluctuations contribute a considerable part of total wind stress in observations, while ERA5 systematically underestimates this contribution (often large than 20%) across all ranges of daily-mean wind speeds. These findings highlight the importance of resolving high-frequency wind variability in studies of air–sea fluxes and upper-ocean dynamics.