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The greater heat losses sustained by the Ligurian-Provenqal basin in winter appear to be the major factor leading to the periodic intrusions of the warmer Tyrrhenian water from the east. This is the main conclusion of a 3-year oceanographic investigation carried out in the eastern Ligurian-Provenqal basin in order to monitor the long-term characteristics of its exchanges with the Tyrrhenian Sea. The analysis of the whole data set collected in this period shows that two currents converge north of Corsica after having flowed along the northwestern side of Corsica (the West Corsican Current) and through the Corsican Channel (the Tyrrhenian Current). While the former does maintain nearly steady properties year round, the latter crosses the strait only during the coldest season, thus showing a clear seasonal trend that begins again every year. The comparison with the meteorological parameters of the Ligurian-Provenqal basin indicates that the winter intrusions of the Tyrrhenian current are tightly associated with the heat and water losses through the rise induced in the upper basin density. In addition to reintegrating the heat lost to the atmosphere, the Tyrrhenian flow might also restore the volume of the basin upper layer involved in the deep water formation processes. This enables us to infer that a unique circulation pattern, mostly driven by atmospheric-climatic conditions, involves the northern part of the western Mediterranean Sea.1.

The principal hydrographic structures and dynamic conditions of the northern Tyrrhenian Sea are studied through the comparison of in situ field data and a modeling simulation. The field observations are long‐term Eulerian and Lagrangian current measurements associated with two hydrographic campaigns conducted in late summer and in winter. The data indicate that a well‐marked cyclonic gyre affecting the water column from the surface to the bottom is present in the northern Tyrrhenian Sea in both periods. The gyre undergoes significant seasonal changes in both shape and size. Following the indications of past studies, a numerical quasi‐geostrophic model driven by the wind jet blowing from the Strait of Bonifacio was able to reproduce the principal gyre characteristics. However, the wind jet alone does not explain all the gyre features, especially its seasonal variation. A study of the model results and field data indicates that these variations are linked to the seasonal variability of the northward surface current flowing along the eastern boundary of the Tyrrhenian Sea.

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The fidelity of corrections and processing are critical for a realistic use of official altimetric products close to the coast. A new processing strategy, which starts from the TOPEX/Poseidon GDRs with the addition of improved corrective terms, is proposed and evaluated in the area of the Corsica Channel. Sea level anomalies agree with the coincident sea truth (bottom pressure and tide gauge) within 2-3 cm rms for seasonal and longer time scales. Analysis for almost ten years of coincident mooring and altimetric velocities shows that a substantial reduction of uncertainty to ∼4 cm s−1 may be possible after reasonable filtering of the noise introduced by more variable coastal sea surface states. The conclusion is that the altimetry success is still limited to seasonal time scales, and provided that the oceanographic signal ensures an adequate signature to be isolated from background noise

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Abstract. In this paper we examine the relationship between the seasonal and interannual variability observed in the water flow through the Corsica Channel and the sea level difference between the Tyrrhenian and Ligurian Seas. The steric contribution to the sea level difference, computed from historical hydrological data, is in good agreement with the stable presence of the seasonal signal in the water exchanges. We obtain the maximum steric difference in winter (-16 cm) and the minimum in summer (-2 cm). These values are consistent with the corresponding estimates of water volume transport (0.8 and <0.1 Sv in winter and summer, respectively). Also, TOPEX/Poseidon (T/P) satellite altimetry is shown to be capable of capturing the sea level difference anomaly between the two basins at seasonal and interannual scales. Accuracy of altimeter data in the study region has been checked using measurements from a bottom pressure recorder deployed in Capraia Island (rms difference is found to be -2 cm after application of a 30-day half-amplitude Gaussian filter). Because of the lack of an accurate geoid, the total water transport cannot be adequately monitored by satellite altimetry alone. However, the recovered signal can be directly related to the water transport anomaly through the channel. The resulting T/P signal can be considered as representing, to a great extent, the real steric variation induced by the net sea surface heat