Abstract
Motivated by the recurrent formation of mesoscale anticyclones in the southeast of Crete, we investigated with a high resolution model the response of the ocean to orographic wind jets driven by the Cretean mountain range. As shown in the dynamical process study of Ioannou et al. (2020) which uses a simplified shallow-water model, we confirm here, using the CROCO (Coastal and Regional Ocean COmmunity) model, that the main oceanic response to the Etesian wind forcing is the formation of mesoscale anticyclones. Moreover, we found that the intensity of the wind-induced Ekman pumping acting on the eddies, once they are formed, modulates their intensity. Among the various coastal anticyclones formed during summer and fall 2015, only one of them will correspond to a long lived structure (M_IE15) which is similar to the Ierapetra Eddy detected in 2015 (O_IE15) on the AVISO/DUACS products. Thanks to the DYNED-Atlas data base, we were able to perform a quantitative comparison of the vertical structure of such long-lived anticyclone between the numerical model and the in-situ measurements of the various Argo profilers trapped inside the eddy core. Even without assimilation or any nudging, the numerical model was able to reproduce correctly the formation period, the seasonal evolution and the vertical structure of the O_IE15. The main discrepancy between the model and the altimetry observations is the dynamical intensity of the anticyclone. The characteristic eddy velocity derived from the AVISO/DUACS product for the O_IE15 is much lower than in the numerical model. This is probably due to the spatio temporal interpolation of the AVISO/DUACS altimetry products. More surprisingly, several coastal anticyclones were also formed in the model in the lee of Crete area during summer 2015 when the Etesian winds reach strong values. However, these coastal anticyclones respond differently to the wind forcing since they remain close to the coast, in shallow-waters, unlike the M_IE15 which propagates offshore in deep water. The impact of the bottom friction or the coastal dissipation seems to limit the wind amplification of these coastal anticyclones.
Highlights
Even if the generation of coastal eddies induced by orographic winds have been documented in several studies, it is still difficult to identify what are the main mechanisms that drive their dynamical characteristics and their vertical extent
The Etesian winds blowing across the complex orography of Crete induce strong wind jets in its wake
The realistic simulation CROCO-MED60v40-2015 reveals that several coastal anticyclones are formed in the Kasos strait area when intense wind-jets, driven by the Etesian winds, occur
Summary
Even if the generation of coastal eddies induced by orographic winds have been documented in several studies, it is still difficult to identify what are the main mechanisms that drive their dynamical characteristics (size and intensity) and their vertical extent. The simultaneous combination of several extra processes (coastal currents, bottom friction, tides...) is often a source of complexity for the analysis of real wind-induced eddies Such eddies could be very intense and/or long-lived, they have a strong impact on the export of coastal nutrients or biogeochemical species into the open sea or the ocean. The formation of both cyclonic and anticyclonic eddies was frequently observed in the lee of oceanic mountainous islands (Barton et al, 2000; Caldeira, 2002; Jiménez et al, 2008; Piedeleu et al, 2009; Yoshida et al, 2010; Jia et al, 2011; Kersalé et al, 2011; Caldeira and Sangrà, 2012; Couvelard et al, 2012; Caldeira et al, 2014). This study focuses on this specific area where intense coastal anticyclones are formed recurrently during the summer months (Larnicol et al, 1995; Matteoda and Glenn, 1996; Hamad et al, 2005, 2006; Taupier-Letage, 2008; Amitai et al, 2010; Menna et al, 2012; Mkhinini et al, 2014; Ioannou et al, 2017)
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