Spatial evolution of surface wave spectrum in the Gulf of Tehuantepec under moderate to strong offshore winds
Francisco Ocampo-Torres(1) , Héctor García(1) , Reginaldo Durazo(2) , and Federico Velázquez(2)
Km 107 Carretera Tijuana-Ensenada,
22860 Ensenada BC,
(2) UABC, Km 106 Carretera Tijuana-Ensenada, 22860 Ensenada BC, Mexico
Analysis of the wave field spatial evolution is performed using data from various sources (in-situ ADPCs and ASIS buoy, and remote sensors such as ASAR from ENVISAT) for the region of the Gulf of Tehuantepec, México. Field measurements were carried out between February and April, 2005. The presence of strong and persistent offshore wind jet events (Tehuano Events) especially during the winter season is a unique characteristic of the study region. Arrival of swell practically over the whole year makes it a region with the opportunity to look in detail to the wave field evolution when locally generated wind sea propagates against the swell. Two 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 swell imaging process is addressed, especially taking into account the direct measurements of momentum flux through ASIS buoy capability. Most of the time the swell depicted by ASAR in this region is azimuthally travelling, and the influence of locally generated waves on the imaging process is also investigated. Detailed comparisons of detected swell for two cases at the final stage of a Tehuano event are performed. For the first case the swell is of higher energy compared to the local wind sea, while for the second case swell is moderate and of similar energy than the locally generated waves. Spatial evolution of swell is very well followed by using ASAR wave spectral determination and some of the variability detected can be attributed to the groupiness nature of the wave field. Swell fields with moderately different characteristics of length and propagation direction are also detected. Some other features associated with the current field are depicted and studied making use of hourly maps of surface current field obtained through a pair of high frequency radars (WERA Systems) deployed for the measuring campaign.