Experimental evidence of long-term oceanic circulation reversals without wind influence in the North Ionian Sea

Rubino, Angelo; Gačić, Miroslav; Bensi, Manuel; Kovačević, Vedrana; Malačič, Vlado; Menna, Milena; Negretti, Maria Eletta; Sommeria, Joël; Zanchettin, Davide; Barreto, Ricardo Viana; Ursella, Laura; Cardín, Vanessa; Civitarese, Giuseppe; Orlić, Mirko; Petelin, Boris; Siena, Giuseppe

doi:10.1038/s41598-020-57862-6

Cited by 40 publications

(58 citation statements)

References 37 publications

(43 reference statements)

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“…Hence, we discuss the effect of different discharge rates of the dense water at the slope on the surface circulation at the open sea attempting to reproduce the circulation inversions in the northern Ionian Sea. Rubino et al (2020), by comparing the results of experiments in the rotating tank with those obtained by a numerical model and altimetry data, show qualitatively that the inversion of the circulation in the Ionian Sea can be solely explained in terms of the onset of the dense water injection over the slope area. Starting from this finding, the present work goals are 1) to study the evolution 90 of potential vorticity fields both in the slope and in the central area of the rotating tank, using the outputs of three different experiments, and 2) to compare them with vorticity obtained from altimetry (surface layer) and model derived (deep layer) flow in the 'real' Ionian.…”

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confidence: 73%

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Comment on os-2020-122

2021

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The North Ionian Gyre (NIG) displays prominent inversions on decadal scales. We investigate the role of internal forcing, induced by changes of the horizontal pressure gradient due to the varying density of the Adriatic Deep Water (AdDW), that spreads into the deep layers of the Northern Ionian Sea. In turn, the AdDW density fluctuates according to the circulation of the NIG through a feedback mechanism named Bimodal Oscillating System. We set up laboratory experiments with a two-layer ambient fluid in a circular rotating tank, where densities of 1000/1015 kg m -3 characterise the upper/lower layer, respectively. From 20 the potential vorticity evolution during the dense water outflow from a marginal sea, we analyse the response of the open-sea circulation to the along-slope dense water flow. In addition, we show some features of the cyclonic/anticyclonic eddies that form in the upper layer over the slope area. We illustrate the outcome of the experiments of varying density and varying discharge rates associated with the dense water injection. When the density is high, 1020 kg m -3 , and the discharge is large, the kinetic energy of the mean flow is stronger than the eddy kinetic energy. On the other hand, when the density is smaller, 1010 kg m -3 , and the 25 discharge is reduced, vortices are more energetic than the mean flow, that is, the eddy kinetic energy is larger than the kinetic energy of the mean flow. In general, over the slope, following the onset of the dense water injection, the cyclonic vorticity associated with a current shear develops in the upper layer. The vorticity behaves in a two-layer fashion, thus becoming anticyclonic in the lower layer of the slope area. Concurrently, over the deep flat-bottom portion of the basin, a large-scale anticyclonic gyre forms in the upper layer extending partly toward a sloping rim. Density record shows the rise of the pycnocline due to the dense 30 water sinking toward the flat-bottom portion of the tank. We show that the rate of increase of the anticyclonic potential vorticity is proportional to the rate of the rise of the interface, namely, to the rate of decrease of the upper layer thickness (i.e., the upper layer squeezing). The comparison of laboratory experiments with the Ionian Sea is made for a situation when the sudden switch from

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confidence: 73%

“…Apparatus, experimental set-up, and the velocity measurement methods at 12 levels within the tank, their horizontal resolution, as well as the conductivity measurements (indicators of the water density) are described in detail by Rubino et al, 2020. Here we report some essential information only.…”

Section: Experimental Designmentioning

confidence: 99%

Comment on os-2020-122

2021

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“…Indeed, the drivers of this process are hypothesized to be either the Adriatic dense water or the local effects of pressure and/or wind-driven patterns (e.g. Molcard et al, 2002;Borzelli et al, 2009;Gačić et al, 2010;Pinardi et al, 2015;Reale et al, 2017;Rubino et al, 2020). Consequently, the AdriSC climate model has also been developed with the aim to expand the knowledge on which driver is most important for modelling the BiOS.…”

Section: Summary and Perspectivesmentioning

confidence: 99%

Performance of the Adriatic Sea and Coast (AdriSC) climate component – a COAWST V3.3-based coupled atmosphere-ocean modelling suite: atmospheric part

Denamiel¹,

Pranić²,

Ivanković³

et al. 2021

Preprint

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Abstract. In this evaluation study, the coupled atmosphere-ocean Adriatic Sea and Coast (AdriSC) climate model, which was implemented to carry out 31-year long evaluation and climate projection simulations in the Adriatic and northern Ionian seas, is briefly presented. The kilometre-scale AdriSC atmospheric results, derived with the Weather Research and Forecasting (WRF) 3-km model for the 1987–2017 period, are then thoroughly compared to a comprehensive publicly and freely available observational dataset. The evaluation shows that overall, except for the summer surface temperatures which are systematically underestimated, the AdriSC WRF 3-km model has a far better capacity to reproduce the surface climate variables (and particularly the rain) than the WRF regional climate models at 0.11° of resolution. In addition, several spurious data have been found in both gridded products and in situ measurements which thus should be used with care in the Adriatic region for climate studies at local and regional scales. Long-term simulations with the AdriSC climate model, which couples the WRF 3-km model with a 1-km ocean model, might thus be a new avenue to substantially improve the reproduction, at the climate scale, of the Adriatic Sea dynamics driving the Eastern Mediterranean thermohaline circulation. As such it may also provide new standards for climate studies of orographically-developed coastal regions in general.

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“…The reversal of basin‐wide gyres in the world ocean can be modulated by the specific basin geometric characteristics (e.g., open ocean versus semienclosed seas and gulfs), changes in wind direction, and the water mass transformation and spreading processes. Some of the most well‐known basin‐scale gyre reversals occur in open ocean areas (Somali current system, Schott & Fischer, 2000, and Prasad & Ikeda, 2002; Bay of Bengal, Eigenheer & Quadfasel, 2000; Beaufort Sea, Preller & Posey, 1989; Northern Ionian Sea, Borzelli et al, 2009, Pinardi et al, 2015, and Rubino et al, 2020) and semienclosed seas and Gulfs (Red Sea, Yao et al, 2014a, 2014b; Gulf of Finland, Liblik et al, 2013; Gulf of California, Carrillo et al, 2002, and Marinone, 2003; Sulu Sea in the Philippine Archipelago, Han et al, 2009; Panama Bight, Devis‐Morales et al, 2008; and the South China Sea, Wu et al, 1998, and Fang et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Observational Evidence of the Basin‐Wide Gyre Reversal in the Gulf of Taranto

Federico

Pinardi

Lyubartsev

et al. 2020

Geophysical Research Letters

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The paper shows for the first time the observational evidence of basin-wide gyre reversal in the Gulf of Taranto (north-western Ionian Sea in the eastern Mediterranean Sea) by means of two specifically designed in situ oceanographic campaigns (based on CTD and ADCP measurements). The analysis of the in situ data shows a change in circulation from anticyclonic in October 2014 to cyclonic in June-July 2016. Furthermore, long-term (1993-2018) analysis using gridded satellite altimetry data in the Gulf of Taranto shows that the cyclonic gyres are more frequent than anticyclonic gyres. The latter occur only for 2 to 3 years at a time in some decades. Plain Language Summary The work shows the observational evidence of a phenomenon named gyre reversal (the circulation changes from cyclonic to anticyclonic), occurring in ocean regions with specific geometry characteristics, among others the Gulfs. In particular, our results unequivocally show for the first time the reversal of the basin-scale gyre circulation in the Gulf of Taranto (north-western Ionian Sea in the eastern Mediterranean Sea), by means of in situ oceanographic measurements and satellite data.

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Experimental evidence of long-term oceanic circulation reversals without wind influence in the North Ionian Sea

Cited by 40 publications

References 37 publications

Comment on os-2020-122

Comment on os-2020-122

Performance of the Adriatic Sea and Coast (AdriSC) climate component – a COAWST V3.3-based coupled atmosphere-ocean modelling suite: atmospheric part

Observational Evidence of the Basin‐Wide Gyre Reversal in the Gulf of Taranto

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