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A new parametric model is developed to describe the wind field asymmetry commonly observed in tropical cyclones or hurricanes in a reference frame fixed at its center. Observations from 21 hurricanes from the North Atlantic basin and TC Roger (1993) in the Coral Sea are analyzed to determine the azimuthal and radial asymmetry typical in these mesoscale systems after removing the forward speed. On the basis of the observations, a new asymmetric directional wind model is proposed which adjusts the widely used Holland (1980) axisymmetric wind model to account for the action of blocking high‐pressure systems, boundary layer friction, and forward speed. The model is tested against the observations and demonstrated to capture the physical features of asymmetric cyclones and provides a better fit to observed winds than the Holland model. Optimum values and distributions of the model parameters are derived for use in statistical modeling. Finally, the model is used to investigate the asymmetric character of TC systems, including the azimuth of the maximum wind speed, the degree of asymmetry, and the relationship between asymmetry and forward speed. A new parametric model for tropical cyclone wind fields is proposed to enable the modeling of wind field asymmetriesThe new asymmetric model improves estimations of tropical cyclone wind fields compared to the conventional Holland (1980) symmetric modelAsymmetric features of historical tropical cyclones are quantitatively investigated using the new model parameters of asymmetry

Field measurements of wind stress over shallow water swell traveling in different directions relative to the wind are presented. The directional distribution of the measured stresses is used to confirm the previously proposed but unverified directional distribution of the wind energy input function. The observed wind energy input function is found to follow a much narrower distribution ( β∝cos⁡3.6θ) than the Plant (1982) cosine distribution. The observation of negative stress angles at large wind‐wave angles, however, indicates that the onset of negative wind shearing occurs at about θ≈50°, and supports the use of the Snyder et al. (1981) directional distribution. Taking into account the reverse momentum transfer from swell to the wind, Snyder's proposed parameterization is found to perform exceptionally well in explaining the observed narrow directional distribution of the wind energy input function, and predicting the wind drag coefficients. The empirical coefficient (ε) in Snyder's parameterization is hypothesised to be a function of the wave shape parameter, with εvalue increasing as the wave shape changes between sinusoidal, sawtooth, and sharp‐crested shoaling waves. Field measurements of wind energy input function are performedExamined previously unverified directional distribution of wind energy inputWave shape effects on wind energy input function are identified

Laboratory measurements of the interaction between high‐frequency (HF) wind‐waves and low frequency (LF) paddle waves are presented. The measurements were made in a wind‐wave flume with wind and paddle waves propagating in the same direction. The primary objective is to examine the physical mechanisms proposed to explain the suppression of wind‐waves due to presence of swell (here paddle waves). For this purpose, the precise time scale of the temporal transition from wind‐only to wind‐plus‐paddle conditions is examined. The results reveal that the majority of wind‐wave suppression occurs too quickly to have been caused by reduced wind‐input, instead indicating that enhanced HF wave dissipation is the primary suppression mechanism. The spatial variation in HF wave energy along the LF wave phase indicates that HF suppression mainly occurs on the LF wave crest, and high on the windward face, which are the locations that experience the highest wind velocities. This observation also suggests that the reduced wind‐input is not the primary suppression mechanism. Quantification of HF wave suppression versus a broad range of wind velocities, paddle wave conditions and fetch did not reveal any critical dependence of suppression on LF wave breaking or wind separation at LF wave crests. It is concluded that suppression occurs primarily due to enhanced dissipation of HF waves near LF wave crests. This mechanism is proposed to be coupled to the wind velocity, where an increased wind velocity near LF wave crests exceeds the level of forcing that HF waves of low C/u*can withstand without breaking. Wind action on water surface results in generation and growth of wind‐waves. Observations have shown that the presence of swell traveling in the wind direction suppresses the wind‐waves. There is however no consensus on the physical mechanisms behind this effect. In this study, the proposed mechanisms are examined through laboratory observations of the interaction between wind‐waves and paddle waves. This includes observations of the precise transition time scale as paddle waves enter an existing wind‐wave field. The rapidity of suppression indicates that wind‐waves are actively erased by paddle waves, more so than being inhibited in their growth which is a slower process. The measurements also reveal that suppression of wind‐waves mainly occurs near the crest of paddle waves, and high on their windward face, which are the locations most exposed to the wind. Both observations indicate that enhanced dissipation of wind‐waves is the primary mechanism of their suppression, while the reduction of wind energy input to wind‐waves only plays a secondary role. The enhanced dissipation of wind‐waves is suggested to be linked to the wind velocity, with wind‐waves breaking at the crest of paddle waves as the excess wind velocity at this location exceeds the threshold the wind‐waves can withstand. Enhanced energy dissipation is the primary mechanism behind wind‐wave suppression during interaction with swellSuppression of HF waves in the presence of LF waves mainly occurs on the LF wave crest, and high on its windward faceLF wave breaking and wind separation from LF waves are not essential for HF waves suppression during swell, but may play a secondary role Enhanced energy dissipation is the primary mechanism behind wind‐wave suppression during interaction with swell Suppression of HF waves in the presence of LF waves mainly occurs on the LF wave crest, and high on its windward face LF wave breaking and wind separation from LF waves are not essential for HF waves suppression during swell, but may play a secondary role