Lagrangian and Eulerian observations of the surface circulation in the Tyrrhenian Sea

Abstract

This paper focuses on the study of the Tyrrhenian Sea, a subbasin of the western Mediterranean whose surface and near‐surface dynamics are still relatively poorly known, in particular, its southern region. Its circulation is described first by a set of 53 surface drifters deployed in the area between December 2001 and February 2004. In order to supplement the drifter data with continuously and uniformly sampled observations and to characterize the seasonal, as well as higher‐frequency variability of the surface circulation, the Lagrangian analysis was associated to simultaneous satellite remotely sensed altimeter, covering the period 2001–2004. The investigation was based on trajectory analysis and on the computation of the pseudo‐Eulerian statistics using the same binning and space‐time averaging for drifter and altimeter data. The data reveal a complex pattern of the circulation, especially in the southern region of the Tyrrhenian, dominated by semipermanent recirculations and transient features, which sometimes makes it difficult to identify a consistent mean flow, while the northern subbasin is characterized by a pair composed of cyclonic and anticyclonic circulations known in the literature as the North Tyrrhenian Cyclone and North Tyrrhenian Anticyclone. The pseudo‐Eulerian statistics computed with the two data sets evidenced the representativeness of a joint analysis of altimeter and drifter data and yielded useful indications about proper preliminary preprocessing and resampling procedures, so as to make the comparison statistically sound.

Lagrangian Transport of Marine Litter in the Mediterranean Sea

“…Observations in the Tyrrhenian rather suggest more abundance in the southern portion of the basin, characterized by very slow, basically stagnating dynamics (Rinaldi et al, 2010; for a discussion see Zambianchi et al, 2014; this is also in agreement with the modeling results by Mansui et al, 2015) and in the Corsica Channel Cózar et al, 2015). The former is not to be seen in our reconstruction, while the latter is compatible with the 1-month results for the CID FLP distribution (Figure 10).…”

“…As a consequence, a winter and a summer season of 6 months each were considered a better choice to ensure statistical significance of the results. In previous studies of the Mediterranean Sea circulation using drifter data two extended seasons were also considered, choosing two opposite periods so as to maximize the differences between the resulting fields (Poulain and Zambianchi, 2007;Rinaldi et al, 2010;Poulain et al, 2012). In particular, the choice of the starting and ending times of the seasons was here optimized considering two different configurations: one with an extended summer starting in May and ending in October and another one starting in June and ending in November.…”

Recent improvements in mesoscale characterization of the western Mediterranean Sea: synergy between satellite altimetry and other observational approaches

“…However, as noted by Rinaldi et al (2010), the circulation appears to be much more complex, with a combination of mesoscale, seasonal and interannual variability. The northwest Tyrrhenian is characterized by the presence of North Tyrrhenian cyclones (Marullo et al 1994), which are driven by northwesterly winds.…”

Plankton in the open Mediterranean Sea: a review

“…Local deep convection events occur periodically in the deep troughs (>1000 m) of the North Aegean Sea and in the deep basin of the South Aegean Sea (Theocharis and Georgopoulos, 1993;Theocharis et al, 1999). In the Gulf of Lion (NW MS), a large scale cyclonic circulation and the extreme atmospheric Artegiani et al, 1997;Malanotte-Rizzoli et al, 1997;Millot, 1999;Astraldi et al, 2002;Karageorgis et al, 2008;Rinaldi et al, 2009). forcing, especially in winter, force intense convective events, which eventually reach the bottom.…”

“…The most important are the cyclonic Rhodos Gyre (NW Levantine Sea) and the South Adriatic Gyre, with convective events during winter leading to the formation of intermediate and deep water masses, respectively. Another quasi permanent gyre, which is mostly wind driven and displays strong seasonality, is located in the North Tyrrhenian Sea (Artale et al, 1994), coupled with anti-cyclonic twin on its southern edge (Rinaldi et al, 2009). In the southern part of the basin, in addition to the Algerian eddies, quasi permanent anticyclonic structures populate the eastern MS, e.g., Ierapetra (south of Crete Island), Mersa Matruh (north of the Egyptian coast), and a more variable multipole anticyclonic structure S and SE of Cyprus, which has recently been analyzed in great detail .…”