Wind-Wave Characterization in a Wind-Jet Region: The Ebro Delta Case

Abstract

This manuscript describes the wind-wave generation, development and fading in a complex area: a wind-jet region. The study region is the offshore Ebro Delta (NW Mediterranean Sea) where strong cross-shelf winds occur due to a topographic channelization. This leads to relatively short-fetch conditions, which interact with the swell component. The third-generation wave model Simulating WAves Nearshore (SWAN) is implemented and fed by high-resolution wind fields. A combination of buoy and High Frequency (HF) radar data is used for model validation, resulting in a reasonable level of agreement. The numerical results characterize the wind-wave evolution during a wind jet. A bimodal spectrum is observed due to the interaction of swell and sea systems. The wave directional spreading exhibits lower values at the wind-jet axis. Finally, a reliability analysis of the wave data from an HF radar deployed at the region is carried out.

Wave–Current Interactions in a Wind-jet Region

“…The wave climate at the Ebro Delta is characterized by the predominance of NW winds (which coincides with the predominance of NW winds), although there are also significant storms from the east and south. These storms tend to develop a bimodal directional spectrum due to the coexistence of wind waves and swell waves (Sánchez-Arcilla et al, 2008;Ràfols et al, 2017b). Local wind waves (sea system) show a broadband spectrum with a high variety of frequencies associated with irregular sea states.…”

“…In contrast, waves generated far away (swell system) present a narrowband spectrum with a frequency range with less associated energy. Then, when the sea and swell systems exist at the same time, bimodal spectra occur (Ràfols et al, 2017b).…”

“…3). These events were previously analyzed in Ràfols et al (2017b), where statistical metrics for each episode were provided. To see the temporal evolution of a wind jet more clearly, in Fig.…”

“…This region is very interesting from a meteo-oceanographic point of view because multiple processes take place, such as bimodal wave spectra and the development of a two-layer cross-shelf flow. Some authors have investigated the circulation patterns (Grifoll et al, 2015;Ràfols et al, 2017a) and the wave field (Bolaños-Sanchez et al, 2007;Grifoll et al, 2016;Ràfols et al, 2017b) during these NW wind-jet events but less efforts have been made at investigating the WCI in the region. Due to the limited observational data, in order to study the wind-jet induced dynamics of the region, the use of numerical models is required.…”

“…The selected study period is from March 15 2014 to May 15 2014 because it contains four wind-jet episodes. Additionally, this period has been previously used to validate numerical models in the study region and the wind-wave characterization (Ràfols et al, 2017b), and water shelf circulation (Ràfols et al, 2017a) was investigated by combining numerical efforts and in situ observations. This work is organized as follows.…”