5 research outputs found
Comparison between XBT data and TOPEX/Poseidon satellite altimetry in the Ligurian-Tyrrhenian area
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 (MFSPP). 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 complementarity in providing a dynamically complete description of the observed structures
Variability of mesoscale features in the Mediterranean Sea from XBT data analysis
Este artĂculo contiene 12 páginas, 10 figuras, 2 tablas.During the period 1998–2000, the Mediterranean
Forecasting System Pilot Project, aiming to build a forecasting
system for the physical state of the sea, has been carried
out. A ship-of-opportunity programme sampled the Mediterranean
upper ocean thermal structure by means of eXpendable
Bathy-Thermographs (XBTs), along seven tracks, from
September 1999 to May 2000. The tracks were designed
to detect some of the main circulation features, such as the
stream of surface Atlantic water flowing from the Alboran
Sea to the Eastern Levantine Basin. The cyclonic gyres in
the Liguro-Provenal Basin, the southern Adriatic and Ionian
Seas and the anticyclonic gyres in the Levantine Basin were
also features to be detected.
The monitoring system confirmed a long-term persistence
of structures (at least during the entire observing period),
which were previously thought to be transient features. In
particular, in the Levantine Basin anticyclonic Shikmona and
Ierapetra Gyres have been observed during the monitoring
period.
In order to identify the major changes in the thermal structures
and the dynamical implications, the XBT data are compared
with historical measurements collected in the 1980s
and 1990s. The results indicate that some thermal features
are being restored to the situation that existed in the 1980s,
after the changes induced by the so-called “Eastern Mediterranean
Transient”This work was funded by the project MAS3-
CT98-0171 of the European Commission. G. Fusco and G. M. R.
Manzella have also been supported by MURST 5% project “AmbienteMediterraneo”.Peer reviewe