Integrated use of altimeter and in situ data for understanding the water exchanges between the Tyrrhenian and Ligurian Seas

In this paper we examine the relationship between the seasonal and interann ual variability observed in the water flow through the Corsica Channel and the sea level difference between the Tyrrhenian and Ligurian Seas. The ster ic contribution to the sea level difference, computed from historical hydro logical 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 (similar to 16 cm) and the minimum in summer (similar to 2 cm). Thes e values are consistent with the corresponding estimates of water volume tr ansport (0.8 and <0.1 Sv in winter and summer, respectively). Also, TOPEX/P oseidon (T/P) satellite altimetry is shown to be capable of capturing the s ea level difference anomaly between the two basins at seasonal and interann ual scales. Accuracy of altimeter data in the study region has been checked using measurements from a bottom pressure recorder deployed in Capraia Isl and (rms difference is found to be similar to 2 cm after application of a 3 0-day half-amplitude Gaussian filter). Because of the lack of an accurate g eoid, 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 c an be considered as representing, to a great extent, the real steric variat ion induced by the net sea surface heat fluxes. The high correlation found between the water transport and sea level difference anomalies confirms the results obtained by the climatological hydrography and provides new eviden ce that interannual differences in the sea level and water transport can be related to the different heat flux balance in the Tyrrhenian and Ligurian Seas. Moreover, it demonstrates, for the first time in the Mediterranean, t he potential of satellite altimetry for long-term monitoring of the water e xchanges between adjacent basins.