The intOA Experiment: A Study of Ocean-Atmosphere Interactions Under Moderate to Strong Offshore Winds and Opposing Swell Conditions in the Gulf of Tehuantepec, Mexico

Abstract

The Gulf of Tehuantepec air-sea interaction experiment (intOA) took place from February to April 2005, under the Programme for the Study of the Gulf of Tehuantepec (PEGoT, Spanish acronym for Programa para el Estudio del Golfo de Tehuantepec). PEGoT is underway aiming for better knowledge of the effect of strong and persistent offshore winds on coastal waters and their natural resources, as well as performing advanced numerical modelling of the wave and surface current fields. One of the goals of the intOA experiment is to improve our knowledge on air-sea interaction processes with particular emphasis on the effect of surface waves on the momentum flux for the characteristic and unique conditions that occur when strong Tehuano winds blow offshore against the Pacific Ocean long period swell. For the field campaign, an air-sea interaction spar (ASIS) buoy was deployed in the Gulf of Tehuantepec to measure surface waves and the momentum flux between the ocean and the atmosphere. High frequency radar systems (phase array type) were in operation from two coastal sites and three acoustic Doppler current profilers were deployed near-shore. Synthetic aperture radar images were also acquired as part of the remote sensing component of the experiment. The present paper provides the main results on the wave and wind fields, addressing the direct calculation of the momentum flux and the drag coefficient, and gives an overview of the intOA experiment. Although the effect of swell has been described in recent studies, this is the first time for the very specific conditions encountered, such as swell persistently opposing offshore winds and locally generated waves, to show a clear evidence of the influence on the wind stress of the significant steepness of swell waves.

Dimensionally Consistent Similarity Relation of Ocean Surface Friction Coefficient in Mixed Seas*

“…This paper presents an analysis of wavelength scaling for the ocean surface friction coefficient in mixed seas using the data from the field experiment of the Gulf of Tehuantepec air-sea interaction experiment (IntOA) from 22 February to 24 April 2005(García-Nava et al 2009Ocampo-Torres et al 2011). Section 2 describes the wavelength scaling similarity relation of ocean surface friction coefficient and the application to field data.…”

On the parameterization of the drag coefficient in mixed seas

“…The highest wind waves occurred during the strongest Tehuano winds, and the highest significant wave height was about 2.5 m at 20 m s -1 wind speed in association with fetch-limited growth (Fig. 2, see also Ocampo-Torres et al (2011).…”

“…An extensive description of the experiment can be found in the paper by Ocampo-Torres et al (2011), while details on data acquisition and processing are given by García-Nava et al (2009).…”

On Offshore wind turbine fatigue caused by wave influenced wind

“…While wind-waves are normally aligned with the local wind, the local wind direction is not always correlated with the swell direction. Sometimes winds can completely oppose the swell field and this is known to give rise to interesting situations with increased turbulence levels over the sea surface [3]. We choose to study cases where the wind is aligned to the wind field and opposing the wind field, and compare these to a control run over a flat surface.…”