The Influence of Sea Sprays on Drag Coefficient at High Wind Speed

Field and laboratory observations indicate that the variation of drag coefficient with wind speed at high winds is different from that under low-to-moderate winds.By taking the effects of wave development and sea spray into account,a new parameterization of drag coefficient applicable from low to extreme winds is proposed.It is shown that,under low-to-moderate wind conditions so that the sea spray effects could be neglected,the nondimensional aerodynamic roughness first increases and then decreases with the increasing wave age;whereas under high wind conditions,the drag coefficient decreases with the increasing wind speed due to the modification of the logarithmic wind profile by the effect of sea spray droplets produced by bursting bubbles or wind tearing breaking wave crests.The drag coefficients and sea surface aerodynamic roughnesses reach their maximum values vary under different wave developments.Correspondingly,the reduction of drag coefficient under high winds reduces the increasing rate of friction velocity with increasing wind speed.

Improving the wind and wave estimation of dual-frequency altimeter JASON1 in Typhoon Shanshan and considering the rain effects

Altimetry data have been widely used in various fiehts of oceanography, including the extreme weather events such as tropical cyclones, typhoons, and hurricanes. The performance of JASON1 in Typhoon Shanshan is assessed by examining the sensor geophysical data record and illustrates how the measured return waveform, significant wave height, and backscatter are all affected by various factors associated with the typhoon, with details by the rain are illustrated. The correction method to maintain accurate wave height and wind speed measurements in Typhoon Shanshan and the results are presented. Furthermore, the additional results of rain rate and typhoon eye diameter can be retrieved. Because of the lack of in-situ measurements of wind, wave, and rain rate at Typhoon Shanshan, results are compared with the forecasted typhoon data and a good agreement is found.

Observation and analysis of the influence of wind waves on air-sea momentum fluxes

Due to the long-standing lack of understanding the role of wind waves on wind stress at moderate to high wind speeds,a high-frequency turbulence observation system is used in this study to obtain air-sea momentum flux data under pure wind wave conditions based on the tower-based marine meteorological observation platform in the southern Bohai Sea.Moreover,the modulation of wind waves on wind stress under wind speeds greater than 10 m s^(–1)is analyzed.The results indicated that the wind wave states caused by winds from the northwest and northeast are different under the influence of cold air,resulting in different wind stresses and drag coefficients.The wind stress increases with an increasing wind speed,reaching its maximum value when the northwest wind is nearly 20 m s^(–1),while the extreme value of the drag coefficient is basically the same when the northwest wind speed is the maximum and the northeast wind wave significant wave height is the maximum.The drag coefficient increases with an increasing wind speed within the range of 10–15 m s^(–1),reaching saturation at 15 m s^(–1).The critical wind speed is smaller than other observed results.Further analysis showed that wind-induced turbulent stress deviates from the observed values,and the degree of deviation depends on the wind speed and wave state,with a greater deviation caused by strong winds and waves.The wave-induced stress can correct the negative deviation between wind-induced turbulent stress and the observed value,and the drag coefficient calculated based on the modified wind stress tends to be close to the observed value overall.