Sea Surface Wind Structure in the Outer Region of Tropical Cyclones Observed by Wave Gliders


Understanding the sea surface wind structure during tropical cyclones (TCs) is the key for study of ocean response and parameterization of air-sea surface in numerical simulation. However, field observations are scarce. In 2019, three wave gliders were deployed in the South China Sea and the adjacent Western Pacific region, which acquired sea surface wind structure of eight TCs. Analysis of the field data suggests that the wave glider-observed surface winds are consistent with most analysis/reanalysis data (i.e., ERA5, Cross-Calibrated Multi-Platform, and National Centers for Environmental Prediction-Global Data Assimilation System) and Soil Moisture Active Passive. Both wave glider observations and analysis/reanalysis data indicate that TC wind fields induce an obvious increase in speed toward the sea surface together with a sharp change in direction, showing an asymmetric wind structure which is sensitive to TC translation speed and intensity. Larger mean values of wind speed and inflow angle are located on the right side along TC tracks. The inflow angle shows a highly dynamic dependence on the radial distance from the TC center, the TC intensity, as well as the TC-relative azimuth. Comparisons between field observations and theoretical models indicate that the most widely used, ideal TC wind profile models can largely represent the observed sea surface wind structure, but generally underestimate the wind speed due to lack of consideration of background wind. Moreover, simple ideal models (e.g., the modified Rankine vortex model) may outperform complex models when accurate information of TCs is limited. Wave glider observations have potential for better understanding of air-sea exchanges and for improvements of the corresponding parameterization schemes.
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