The greater heat losses sustained by the Ligurian-Proven¿al 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-Proven¿al 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-Proven¿al 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. ¿ American Geophysical Union 1992