Surface Wave Field from Altimetry for Mixed Seas (sea and swell) under the Influence of Offshore Winds
Francisco Ocampo-Torres(1) and Héctor García(1)
Km 107 Carretera Tijuana-Ensenada,
22860 Ensenada BC,
Analysis of the wave field is carried out from altimetry data from various sources (ERS-1, ERS-2, TOPEX-POSEIDON) for the region of the Gulf of Tehuantepec, México. The study area is characterized by the presence of strong and persistent offshore wind jet events (Tehuano Events) especially during the winter season. Arrival of swell practically over the whole year makes it a region with the unique opportunity to look in detail the wave field detected by the altimeters when locally generated wind sea propagates against the swell. Histograms of significant wave height (Hs) are analyzed for seasons under Tehuano events and compared to those for the rest of the year. During Tehuano events Hs histograms are wider in distribution resembling the presence of higher waves. A different approach for the analysis, based on Hs information for individual tracks, allows us to perform an evaluation of wave growth under opposing swell conditions. Individual track Hs measurements are compared to in situ observations carried out for a short period of time during the 2005 Tehuano season, when a couple of ADCP with wave measuring capabilities and an Air-Sea Interaction Spar (ASIS) buoy were deployed in the study area. While the ADCPs were mounted at the bottom in 20m water depth, providing us with directional spectrum estimates of the arriving swell, the ASIS buoy provided us with offshore wave information, at a region with 60m water depth. The potential influence of the wind stress on the determination of the significant wave height from the altimeter signal is to be addressed in this work, specifically from direct measurements of the momentum flux with ASIS buoy capability.