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High frequency radars (HFR) are systems that allow us to monitor some oceanographic variables through the backscatter signal from the ocean surface. Typically, they provide us with a relatively high space-time resolution of surface currents and the wave field, very important local information to be used for maritime operation applications, such as search and rescue, safety at sea and transportation, and marine energy resources assessment. Although the main product from HFR is ocean surface currents, they can in addition, provide useful information to derive important characteristics of the wave field, such as significant wave height (Hs) and even the directional spectrum. We, nevertheless, focus our attention in this work in the wave field, and specifically Hs values. A HFR (WERA system) is in operation in Todos Santos Bay, Ensenada, Mexico, since March 2021. Maps of significant wave height are estimated every hour over an area of approximately 250 km2 with spatial resolution of 800 m. These measurements have been compared with wave data derived from three moored instruments (ADCP), the results yielded correlations greater than 0.7 and RMSE values less than 40 cm. In the last two decades this technology has been implemented throughout the world, although there is very limited detail on calibration and validation of the instrument with local ocean wave conditions, especially with respect to the presence of swell. In this study, an empirical calibration is performed using an algorithm provided by the manufacturer in which a correction parameter is obtained according to the operating frequency of the radar, in particular a WERA system. This study takes into consideration some particular characteristics of the area of interest and the performance of the correction parameter is determined as a function of the wave height and direction of travel relative to the radial direction from the WERA site.

Ocean surface wave full directional spectrum is estimated directly from measurements obtained with a spar buoy and from synthetic aperture radar images of the sea surface. These two techniques complement each other to provide us with a rather comprehensive view of the dynamical behaviour of surface waves. We focus our study in sea state conditions under varying winds, when frequently mixed sea and swell systems are encountered. These conditions are characterized by non-equilibrium wind-wave systems. Direct measurements of ocean-atmosphere momentum fluxes obtained from dedicated air-sea interaction spar buoy are also analyzed. The aim is to better understand the ocean-atmosphere momentum transfer behaviour and uppermost ocean currents under rapidly varying wind field. Atmospheric cold front passage through the measuring buoy imposed a unique wind-wave system information, especially under the occurrence of cases when swell propagation opposes locally generated wind-waves. Of particular importance is the analysis of the wave field making use of synthetic aperture radar images of the sea surface. The wave and wind fields to both sides of the atmospheric front are analyzed. From the buoy measurements fetch-limited wind sea growth is also determined, where slanting fetch is to be considered as very relevant. In particular, wind acceleration effect on wave growth is addressed, during specific cases when wind direction prevailed relatively constant. Wind-wave growth rate is somewhat greater than stationary conditions, as it can be observed also in some laboratory experiments at least for the early stages of the growth process.

There is great interest in acquiring directional ocean surface wave direct measurements in order to better determine sea state conditions in open waters as well as in harbors and nearshore sites. Typical applications range widely over coastal and oceanic engineering, naval architecture and safety at sea, for design and construction of vessels and infrastructure, as well as for maintenance and marine operations. In this work we explore the influence of the buoy motion and we are able to detect some turbulence characteristics of the near surface flow. Full motion of the buoy structure is recorded by an Inertial Motion Unit within the velocimeter case, and after applying motion corrections directional wave and some turbulence characteristics are analyzed. The buoy responde is readily defined and the final results are compared with corresponding measurements from a bottom fixed acoustic Doppler current profiler. Details of the groupinness behaviour of the wave field in a nearshore site are given, showing some enhancement of turbulence intensity during the passage of relatively high wave groups. Some attempts to quantify the kinetic energy dissipation rate are explained. Final results show similar turbulence intensity values from the buoys measurements when compared with those from the fixed ADCP.

It is generally accepted that the typical average wind field in a hurricane is well described by a parametric Holland model. The spatial distribution of winds can be determined from data provided by the National Hurricane Center with a 6-hour regularity. The wave field can be calculated by a numerical model from the temporal interpolation of these wind fields. However, a characteristic of wind fields calculated by parametric models is that their spatial and temporal variability are relatively smooth compared to wind fields computed by a high-resolution dynamic model, such as the HWRF. This study analyses the effect of the high temporal and spatial variability of the wind field in a hurricane and its effect on the variability of the wave field calculated by the third-generation wave model Wavewatch III. The wind fields obtained from the use of the HWRF model correspond to the simulation of Hurricane Isaac while crossing through the Gulf of Mexico between 27 and 29 August 2012. The wind fields have a spatial resolution of approximately 2 km and a temporal resolution of 15 minutes. This information is used by an implementation of the Wavewatch III model in the Gulf of Mexico to obtain wave fields with a spatial resolution of 2 km and a temporal resolution of 15 minutes. We find that, despite the high temporal and spatial variability, the mean wind field has a spatial pattern similar to that described by the parametric models. In contrast, the wave field computed by the wave model is much more stable and has a typical structure already described in other studies: large values of significant height in the region of the first quadrant of the hurricane and at the front of its path, with maximum values at distances between one and two times the radius of maximum winds. Smaller values of significant height are found behind the hurricane's track, especially in the third quadrant. The structure of the wave field is largely determined by the translation speed of the storm and the extended fetch effect in the quadrants to the right of the hurricane's path.

The spatial structure of the wave field during hurricane conditions is studied using the National Data Buoy Center directional wave buoy data set from the Caribbean Sea and the Gulf of Mexico. The buoy information, comprising the directional wave spectra during the passage of several hurricanes, was referenced to the center of the hurricane using the path of the hurricane, the propagation velocity, and the radius of the maximum winds. The directional wave spectra were partitioned into their main components to quantify the energy corresponding to the observed wave systems and to distinguish between wind-sea and swell. The findings are consistent with those found using remote sensing data (e.g., Scanning Radar Altimeter data). Based on the previous work, the highest waves are found in the right forward quadrant of the hurricane, where the spectral shape tends to become uni-modal, in the vicinity of the region of maximum winds. More complex spectral shapes are observed in distant regions at the front of and in the rear quadrants of the hurricane, where there is a tendency of the spectra to become bi- and tri-modal. The dominant waves generally propagate at significant angles to the wind direction, except in the regions next to the maximum winds of the right quadrants. Evidence of waves generated by concentric eyewalls associated with secondary maximum winds was also found. The frequency spectra display some of the characteristics of the JONSWAP spectrum adjusted by Young (J Geophys Res 111:8020, 2006); however, at the spectral peak, the similarity with the Pierson–Moskowitz spectrum is clear. These results establish the basis for the use in assessing the ability of numerical models to simulate the wave field in hurricanes.

Se estudia la estructura espacial del campo de olas durante condiciones de huracán usando la base de datos de las boyas direccionales del Centro Nacional de Datos de Boyas (NDBC) del mar Caribe y el Golfo de México. La información recopilada consiste en espectros direccionales del oleaje durante el paso de 14 huracanes y se analiza una vez referenciada con respecto al centro del huracán, la dirección de avance y el radio de vientos máximos. Se identificaron las principales componentes del espectro direccional con el fin de cuantificar la energía generada localmente . Los resultados son consistentes con aquellos encontrados utilizando datos obtenidos por sensores remotos (por ejemplo, datos de altimetría del radar de barrido). En los cuadrantes derechos (con respecto a la dirección de avance del huracán), cerca de la región de vientos máximos, la energía dominante es generada localmente y la forma del espectro tiende a ser unimodal mientras que en los cuadrantes izquierdos la energía dominante es generada en otras regiones del huracán. Del lado izquierdo, y en regiones alejadas enfrente y atrás del centro del huracán, se observan espectros con una estructura más compleja llegando a ser bimodales y trimodales. Las olas dominantes generalmente se propagan a la derecha de la dirección del viento, excepto en la región de vientos máximos de los cuadrantes derechos donde la diferencia con la dirección del viento es mínima. El mismo análisis fue hecho diferenciando entre huracanes menores (categorías 1 y 2) y mayores (categorías 3 a 5). En ambos casos la direccionalidad de la energía es similar en todos los cuadrantes. La diferencia radica en la presencia y la forma de la porción correspondiente alswell en cada cuadrante. Se encontraron evidencias de olas generadas por vientos máximos secundarios asociados a paredes concéntricas al ojo del huracán, las cuales también alcanzan un máximo desarrollo. Los espectros en frecuencia presentan características del espectro tipo JONSWAP formulado por Young (2006)sin embargo es notable la similitud con el espectro tipo Pierson-Moskowitz característico de mares completamente desarrollados. Usando el modelo espectral de predicción del oleaje SWAN se analizó el efecto que tienen la velocidad de avance del huracán y la presencia de paredes concéntricas en la evolución y el desarrollo del campo de olas y en la forma del espectro direccional. Para esto se utilizó un campo de vientos de HRD del huracán Dean del 20 de agosto a las 7:30 (UTC), el cual se propagó con dos velocidades diferentes (5 y 10 m/s). También se impuso en el campo de vientos una pared concéntrica idealizada (que consiste en una función Gaussiana que evolucionan en el tiempo a lo largo de un trayectoria en forma de una espiral de Arquímedes). El modelo representa adecuadamente la direccionalidad de la energía y la forma de los espectros direccionales en el dominio del huracán. Los resultados del modelo indican que tanto el avance de la tormenta como la presencia de paredes concéntricas influyen en el desarrollo de las olas, lo que es consistente con las observaciones. The spatial structure of the wave field during hurricane conditions is studied using the National Data Buoy Center directional wave buoy data set in the Caribbean Sea and the Gulf of Mexico. The buoy information, comprising the directional wave spectra during the passage of several hurricanes, was referenced to the center of the hurricane using the path of the hurricane, the propagation velocity, and the radius of the maximum winds. The directional wave spectra were partitioned into their main components to quantify the energy corresponding to the observed waves systems, and to distinguish between wind-sea and swell. The findings are consistent with those found using remote sensing data (e.g., Scanning Radar Altimeter data). Based on previous work, the highest waves are found in the right forward quadrant of the hurricane, where the spectral shape tends to become uni-modal, in the vicinity of the region of maximum winds. More complex spectral shapes are observed in distant regions at the front of and in the rear quadrants of the hurricane, where there is atendency of the spectrato be come bi-and tri-modal.The dominant waves generally propagate at significant angles to the wind direction, except in the regions next to the maximum winds of the right quadrants. The same analysis was made for two hurricane conditions: minor hurricanes (categories 1 and 2) and major hurricanes (categories 3,4and5).In both cases the directionality of the energy is similar in all quadrants.The difference lies in the presence and the shape of swell energy in each quadrant. Evidence of waves generated by concentric eyewalls associated with secondary maximum winds was also found. The frequency spectra display some of the characteristics of the JONSWAP spectrum adjusted by Young (2006); however, at the spectral peak the similarity with the Pierson-Moskowitz spectrum is clear. These results establish the basis for assessing the ability of numerical models to simulate the wave field in hurricanes.Thre enumerical experiments using the spectral wave prediction model SWAN were carried out to gain insight into the mechanism that controls the directional and frequency distributions of hurricane wave energy. The aim of the experiments is to evaluate the effect of the translation speed of the hurricane and the presence of concentric eye walls, on both the wave growth process and the shape of the directional wave spectrum. The HRD wind field of Hurricane Dean on August 20 at 7:30 was propagated at two different velocities (5 and 10 m/s). An idealized concentric eye wall (a Gaussian function that evolve in time along a path in the form of an Archimedean spiral) was imposed to the wind field. The white-capping formulation of Westhuysen et al. (2007) was selected for the wave model implementation. The wave model represents fairly well the directionality of the energy and the shape of the directional spectra in the hurricane domain. The model results indicate that the forward movement of the storm influences the development of the waves, consistent with field observations.