Three-Dimensional Evolution of Mesoscale Anticyclones in the Lee of Crete

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.

Strong Long‐Lived Anticyclonic Mesoscale Eddies in the Balearic Sea: Formation, Intensification, and Thermal Impact

“…Notice that in the Eastern Mediterranean Sea, Ioannou et al. (2020a, 2020b) also reported intense and recurrent mesoscale anticyclones in the lee of Crete forced by an orographic wind jet produced by the channeling and deflection of the Etesian winds by the island, showing similarities with the orographic effect of the Pyrenees as highlighted here. The authors confirmed that these winds were necessary but not sufficient to form the eddies and suggested that this mechanism had to be reinforced by some other baroclinic process.…”

Cyclone‐Anticyclone Asymmetry of Eddy Detection on Gridded Altimetry Product in the Mediterranean Sea

“…In addition to this statistical validation against altimetric data, Ioannou et al. (2020) showed that the numerical solution CROCO‐MED60v40‐15‐16 exhibits realistic mesoscale features even after 3 years of free simulation: some of these features are even very commensurable with observations (density anomaly, main dynamical parameters, and tracking of a mesoscale eddy). More generally the simulated hydrology has been systematically compared to the CORA v5.2 data set and to SST fields from Meteosat SEVIRI imager.…”

Cyclone-Anticyclone asymmetry of eddy detection on gridded altimetry product in the Mediterranean Sea 

“…However, due to the high spatial resolution of the numerical model, small scale patterns such as the North Ligurian current and the Rhodes Gyre current appear to be much stronger in CROCO-MED60v40. Besides this statistical validation against altimetric data Ioannou et al (2020) showed that the numerical solution CROCO-MED60v40-15-16 exhibits realistic mesoscale features even after 3 years of free simulation : some of these features are even very commensurable with observations (density anomaly, main dynamical parameters and tracking of a mesoscale eddy). More generally the simulated hydrology has been systematically compared to the CORA v5.2 dataset and to SST fields from Meteosat SEVIRI imager.…”