Interannual Variations of Surface Currents and Transports in the Sicily Channel Derived From Coastal Altimetry

Abstract

A 20 year coastal altimetry data set (X‐TRACK) is used, for the first time, to gain insight into the long‐term interannual variations of the surface circulation in the Sicily Channel. First, a spectral along with a time/space diagram analysis are applied to the monthly means. They reveal a regionally coherent current patterns from track to track with a marked interannual variability that is unequally shared between the Atlantic Tunisian Current and Atlantic Ionian Stream inflows in the Sicily Channel and the Bifurcation Tyrrhenian Current outflow northeast of Sicily. Second, an empirical altimetry‐based transport‐like technique is proposed to quantify volume budgets inside the closed boxes formed by the crossing of the altimetry tracks and coastlines over the study area. A set of hydrographic measurements is used to validate the method. The inferred altimetry transports give a well‐balanced mean eastward Atlantic Waters baroclinic flow of 0.4 Sv and standard deviations of 0.2 Sv on a yearly basis throughout the Sicily Channel and toward the Ionian Sea, which is fairly coherent with those found in the literature. Furthermore, the analysis allows to quantify the intrusions of Atlantic Waters over the Tunisian Shelf (0.12 ± 0.1 Sv) and highlights two main modes of variability of the main surface waters path over the Sicily Channel through the Bifurcation Atlantic Tunisian Current and Atlantic Ionian Stream systems. Some physical mechanisms are finally discussed with regards to changes in the observed currents and transports.

Sea Surface Circulation Structures in the Malta-Sicily Channel from Remote Sensing Data

“…Due to baroclinic instabilities, the Atlantic current (AC) regularly forms meanders that eventually detach from the current and become either cyclonic or anticyclonic eddies [36] like the ones observed by Jouini et al [3] and Jebri et al [37,38]. Figure 3 shows the SC inter-annual geostrophic circulation derived from the ADT data depicting some of the AC-born structures described in Jouini et al [3] and Menna et al [5] such as the cyclonic Medina Gyre (MG), the cyclonic Messina Rise Vortex (MRV), the anticyclonic Pantelleria Vortex (PV, which in the literature is mentioned as cyclonic), the anticyclonic MSG, the AIS, the Bifurcation Atlantic Current (BAC) and the Atlantic Tunisian Current (ATC).…”

“…It is characterized by a velocity of~25 cm s −1 and occasionally reaching values higher than 50 cm s −1 . This current consists mainly of AW and changes properties as it passes through the SS deepening and bifurcating into the Ionian Sea northwards or to the Central Ionian Sea depending on the NIG phase [19,21,23,38]. Additionally, the ADT and SGV also show another yet unidentified mesoscale structure close to the coast of Tunisia detached from the ATC, and a shift of the MG eastwards.…”

Physical oceanography of New Zealand/Aotearoa shelf seas – a review

“…Coastal altimetry is one such advance (e.g. Jebri et al 2017) that can provide long-term perspectives on transport and variability. These remote approaches typically do not provide sub-surface information.…”

Determining Undersampled Coastal Tidal Harmonics Using Regularized Least Squares

“…Multiple aspects of the technological advance drive the technological improvement such as new platforms with proven altimetry precision and accuracy and new and dedicated data processing schemes (Passaro et al, 2014(Passaro et al, , 2018. The breakthrough of coastal altimetry technology empowered a series of applications, for example, the estimation of ocean currents (Jebri et al, 2016(Jebri et al, , 2017Salazar-Ceciliano et al, 2018;Valle-Rodríguez & Trasviña-Castro, 2017), inland flow (Biancamaria et al, 2017;Gleason & Durand, 2020), tidal mixing fronts (Dong et al, 2018), tidal energy dissipation (Egbert & Ray, 2001), storm surge heights (Ji et al, 2019), and vertical land motion (Oelsmann et al, 2020). Because this technology is free of clouds or significant weather impacts (Wang, 2022b), it is consid ered an ideal tool to continuously monitor the Earth's surface.…”