Numerical study of eddy generation in the western part of the Gulf of Lion

Abstract

[1] A realistic numerical model is used to investigate the generation process of anticyclonic eddies located in the western part of the Gulf of Lion. During 8 years of simulations from 2001 to 2008, 8 anticyclonic coastal eddies with a life duration longer than 15 days have been observed in the study area between July and early October. The formation process of eddies is linked to the wind stress curl in the area. Nonetheless a simpler criteria can be used examining the changes in the wind amplitude at a key coastal station. The influences of this factor and of the stratification conditions over the study area are investigated, alone or combined, regarding the eddy's formation process. Our results show that these eddies need two conditions to be generated: a persistent and strong northwest wind and a strong stratification. The Ekman transport associated to such a wind and the coastline shape characterized by the presence of capes can create a pressure gradient generating an anticyclonic circulation. At the same time, a strong stratification condition allows a better transfer of wind-induced potential energy to eddy kinetic energy. Persistent wind bursts are also required to sustain the eddy in size and intensity. The present work contributes to a better understanding of the hydrodynamics of the Gulf of Lion.

Physical characteristics and dynamics of the coastal Latex09 Eddy derived from in situ data and numerical modeling

“…Hereafter, we adopt the terminology introduced by Hu et al . [] who defined long‐life eddies as the ones that last for at least 15 days. We have thoroughly studied year 2009 and two modeled long‐life anticyclonic eddies are identified.…”

“…These facts indicate that the generation process of the eddy A1 corresponds to the one described by Hu et al . [] for all long‐life eddies between 2001 and 2008.…”

“…It produces a localized upwelling south of Cape d'Agde but smaller than the one observed in the generation process proposed by Hu et al . []. During this generation process, the wind can be classified on 6 August as a strong northwesterly wind event (16 m s − 1 ), but not persistent because its occurrence during the last three days is less than 75%.…”

“…The generation process of the eddies mentioned by Hu et al . [, 2011a] required two conditions: a persistent and strong northwest wind and a strong stratification [ Hu et al ., ].…”

The role of the wind in the formation of coherent eddies in the Gulf of Eilat/Aqaba

“…Based on observations and modeling, previous studies have suggested various factors for eddy formation, such as the effect of bottom topography or irregular structure of the coastline (Kim, 2010;Zimmerman, 1981), spatial patterns in the wind field (Chavanne et al, 2002;Hu et al, 2011;Oey, 1996;Oey et al, 2001), shear flows (Shapiro et al, 1997) and the interplay of these factors with stratification and tidal forcing (Takeoka and Murao, 1993;Vethamony et al, 2005). Berman et al (2000) used a wind-driven numerical model to show the existence of a chain of cyclonic and anticyclonic eddies, semi-permanently residing along the main axis of the gulf.…”