Comparison between XBT data and TOPEX/Poseidon satellite altimetry in the Ligurian-Tyrrhenian area

Abstract

Abstract. From September 1999 to December 2000, eXpendable Bathy-Thermograph (XBT) profiles were collected along the Genova-Palermo shipping route in the framework of the Mediterranean Forecasting System Pilot Project (MF-SPP). The route is virtually coincident with track 0044 of the TOPEX/Poseidon satellite altimeter, crossing the Ligurian and Tyrrhenian basins in an approximate N-S direction. This allows a direct comparison between XBT and altimetry, whose findings are presented in this paper. XBT sections reveal the presence of the major features of the regional circulation, namely the eastern boundary of the Ligurian gyre, the Bonifacio gyre and the Modified Atlantic Water inflow along the Sicily coast. Twenty-two comparisons of steric heights derived from the XBT data set with concurrent realizations of single-pass altimetric heights are made. The overall correlation is around 0.55 with an RMS difference of less than 3 cm. In the Tyrrhenian Sea the spectra are remarkably similar in shape, but in general the altimetric heights contain more energy. This difference is explained in terms of oceanographic signals, which are captured with a different intensity by the satellite altimeter and XBTs, as well as computational errors. On scales larger than 100 km, the data sets are also significantly coherent, with increasing coherence values at longer wavelengths. The XBTs were dropped every 18-20 km along the track: as a consequence, the spacing scale was unable to resolve adequately the internal radius of deformation (<20 km). Furthermore, few XBT drops were carried out in the Ligurian Sea, due to the limited north-south extent of this basin, so the comparison is problematic there. On the contrary, the major features observed in the XBT data in the Tyrrhenian Sea are also detected by TOPEX/Poseidon. The manuscript is completed by a discussion on how to integrate the two data sets, in order to extract additional information. In particular, the results emphasize their complementariety in providing a dynamically complete description of the observed structures.

Results of the first Wave Glider experiment in the southern Tyrrhenian Sea

“…In the surface layer, these structures are mainly driven by wind and its spatial variability, especially in the northern and central TYS. Some quasi-permanent features characterize the western part of the basin: a wide cyclonic area frequently observed southeast of Sardinia and a cyclonic-anticyclonic system just east of the Bonifacio Strait Millot, 1999;Vignudelli et al, 2003;Budillon et al, 2009). The southern part of the basin is more influenced by the recirculation processes occurring at its meridional openings, as confirmed by the analyses of drifter trajectories presented by Rinaldi et al (2010).…”

“…Over the years, the presence of gyre structures in both seasons has been extensively described using in situ data (Krivosheya and Ovchinnikov, 1973) as well as satellite sea surface temperature (SST) images (Marullo et al, 1994) and altimetry data (Vignudelli et al, 2003). All these studies reported the presence of quasi-permanent and intermittent cold and warm structures even if only few detailed works exist about their formation and evolution (Artale et al, 1994;Pierini and Simioli, 1998).…”

Improved satellite altimetry in coastal systems: Case study of the Corsica Channel (Mediterranean Sea)

“…The Mediterranean Sea is a suitable region where to assess the quality of available altimetric products and the achievable improvements therein. Over the past decade, work has been done at basin scale [e.g., Larnicol et al , 1995] or in specific open sea regions [e.g., Vignudelli et al , 2003]. Close to the coast, altimetric observations often are of lower accuracy or not interpretable due to a number of factors including footprint land contaminations (altimeter and radiometer), inaccurate tidal corrections and incorrect removal of atmospheric (wind and pressure) effects at the sea surface.…”

Heavy Guadalquivir River discharge detection with satellite altimetry: The case of the eastern continental shelf of the Gulf of Cadiz (Iberian Peninsula)

“…A number of initiatives have been made in the last decade to improve the accuracy and availability of altimeter data in the coastal zone. They are applied to along-track measurements (Vignudelli et al, 2005;Roblou et al, 2007;Brown, 2010;Liu et al, 2012), including the use of coastal-oriented corrections and the review of the data recovery strategies near the coast (Vignudelli et al, 2003(Vignudelli et al, , 2005(Vignudelli et al, , 2011 http://dx.doi.org/10.1016/j.asr.2014.12.039 0273-1177/Ó 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.…”