Interannual and interseasonal variability of the surface circulation in the Gulf of Naples (Southern Italy) derived by HF radar observations and comparison with model results.

The results of a study that was performed on the surface circulation of a coastal area using data provided by an HF coastal radar are presented. The surface circulation in the Gulf of Naples (southern Tyrrhenian Sea, western Italian coast), as derived by measurements collected by an HF radar, displayed recurrent dynamics directly linked to prevailing forcing conditions. Depending on the scales of interest, the observed surface current pattern can be characterized by high frequency fluctuations related to tidas and see breeze regime, by frequencies typically associated with the passages of mesoscale atmospheric disturbances which determine change in the surface current field on time scales of about 3 days, and by longer time scales, which represent the focus of our research. Based on a six year (2007-2012) period of surface current observations, our results are relative to the variability at long time scales, from seasonal to interannual.

An analysis in terms of Empirical Orthogonal Functions (EOFs) was carried out in order to study the variability of the HF radar fields and to detect the principal modes at the scales of interest. EOF analysis requires the input data to be continuous so first the data set used for this study has been interpolated in order to fill the gaps both in time and in space and then the EOF applied on seasonal and next yearly time series. The results are integrated with a three-dimensional coastal circulation model at high resolution and forced by realistic daily forcing. The numerical model allows to further investigate the spatial characteristics of dynamical structures, their generation process and their role in the dynamics governing the circulation of the basin