Wave and wind forces from tropical cyclones are one of the main design parameters of coastal and offshore infrastructure in tropical areas. The estimation of ocean waves parameters in the design of structures in tropical areas is difficult due to the complexity of wind fields associated with tropical cyclones. The use of numerical wave models, forced with parametric wind fields, is a common practice within the climatic characterization of extreme events. However, there is currently no consensus on the selection of parametric models for wave prediction due to the lack of a rigorous assessment of different models. In this study, six well-known parametric wind models were tested, compared, and applied in the Gulf of Mexico and the Caribbean Sea. Therefore, the evaluation and comparison of the resulting wind and wave fields are presented, showing that a particular model may best represent a specific event, but, when dealing with a large number of events, the choice of a particular parametric wind model or a combination of them does not guarantee greater accuracy.

a b s t r a c tThe energy and momentum transfer between the atmosphere and the ocean has typically been studied for conditions where the waves have almost or already reached a local equilibrium with a uniform wind. The purpose of this work is to investigate the early stages of the generation of waves under non-stationary wind conditions and to describe the momentum and energy exchange at the airwater interface for non-equilibrium wind conditions. Some experiments with a characteristic wind acceleration were conducted in a large wind-wave facility at the Institut Pythéas (Marseille-France). Momentum fluxes were estimated through hot-wire anemometry and, the free surface displacement was measured along the wave tank by resistance and capacitance wire probes. Wind speed and water elevation measurements were acquired at a high sampling rate. During the experiments, the wind speed was increased with a constant acceleration over time, reaching a constant maximum intensity of 13 ms −1 . Under accelerated wind conditions, the degree of wave field development associated with a certain value of wind speed depends on the wind acceleration. Accordingly, once the rough flow regime is established, the drag coefficient values associated with a certain wind speed also vary depending on wind acceleration. It was observed that higher wind speed is needed to reach a rough flow regime as the wind acceleration increases. Also, the momentum transfer is reduced as wind acceleration increases. Under the rough flow regime, a less developed wave field induces a higher increase of drag coefficient with wind speed.

<p>Direct measurements have been conducted from a spar buoys deployed in the Gulf of Mexico, and in the vicinity of Todos Santos Island, offshore Ensenada BC, Mexico, in order to better understand ocean surface wave modulated processes under a variety of oceanographic and meteorological conditions. Full ocean surface wave directional spectrum is estimated from sea surface elevation data acquired with an array of capacitance wires, to represent directional spectrum as a function of frequency and direction, as well as a function of the wave number components Kx and Ky. Momentum transfer between ocean and the atmosphere is calculated directly through the eddy correlation method applied to wind velocity components acquired with a sonic anemometer. Momentum transfer variability is analysed to study its dependance on the surface wave conditions, with special emphasis on mixed sea states. Comparison between single peak spectra results with those cases where bi-modal spectra were present are performed in order to detect wind stress variability effects. Ocean-atmosphere transfer of momentum is studied and explained in terms of the shape and evolution of the surface wave spectrum. This research is funded by SENER-CONACYT 249795 and 201441 projects.</p>

<div> <div> <div> <p>A determined shape of the energy wave spectrum can be estimated from a given fetch and wind speed. Also, several studies have characterized the balance of the turbulent kinetic energy under the effect of waves and currents under constant wind conditions. However, deeper research is needed in order to characterize the wind-wave generation processes under non-stationary wind conditions. In this way, to be able to determine the uncertainty on not considering accelerated wind events in the air-sea momentum exchange estimations.</p> <p>Periods of accelerated winds were analyzed from experimental and field data. On one hand, several laboratory experiments were carried out in a large wind-wave facility at the Institut Pytheas (Marseille-France). Momentum fluxes were estimated from hot wire anemometry and, the free surface displacement was measured along the wave tank by resistance and capacitance wire probes. Also, the surface drift current was measured from a profiling acoustic velocimeter. During these experiments, the wind speed goes from 2 m/s to reach the maximum wind speed of 13 m/s. A constant wind acceleration characterizes each test. On the other hand, the field data were obtained from an Oceanographic and Marine Meteorology Buoy (BOMM) located in the Gulf of Mexico, from July 2018 to February 2019. The BOMM was equipped with a sonic anemometer, capacitance wires, and an inertial motion unit. Both sets of data are characterized by a high sampling rate that allows us to directly estimate the wind stress over the sea surface. Also, provide us with useful information about the evolution of the wave spectra and enable us to determine the dissipation rate of turbulent kinetic energy. It was observed that the wind acceleration has a direct effect on the momentum transfer efficiency from the wind to the wave field and that the momentum transfer is reduced as wind acceleration increases.</p> </div> </div> </div>

A comprehensive analysis of the wavefield evolution under accelerated wind conditions provides an essential contribution to understanding the wind-wave generation process. A set of experiments was carried out in a large wind-wave facility where it is possible to reproduce high wind speed conditions to study the wind acceleration effect in the wind-wave development.The facility was equipped with high-frequency sampling devices that provide accurate air turbulence and water surface displacement measurements. From this deployment, it was possible to describe the evolution of the wave characteristics under different magnitudes of constant wind acceleration in detail. This study analyzes the wind acceleration effect in the early stages of windwave generation and evolution. The increase of spectrum energy saturation level and the downshift of the peak frequency are processes associated with the spectral shape evolution under low acceleration wind conditions. Under high wind acceleration conditions, the spectral shape did not vary with wind speed and fetch. Despite under low acceleration wind conditions, the wavefield is more developed than under high acceleration wind conditions; there was no direct relation between wind acceleration and the wavefield efficiency to grow. Besides, during these early instants, it was observed that a more developed wave field, associated with low acceleration wind conditions, could slow down the increase of drag coefficient with wind speed.