Seasonal variability of inertial oscillations in the Northern Adriatic

The inertial content of the current time series taken at two stations in the Northern Adriatic between May 1988 and November 1990, and hydrographic data measured at the same stations in the period 1966–1991, were analyzed. The object of the investigation was to document the seasonal variability of the inertial signal and its decay time. It was shown that amplitudes of the inertial oscillations are maximal in summer, having an average surface value of about 10 cm s−1, and that they are within the noise level throughout winter. Such variation is due to seasonal changes in the static stability of the water column, and is also influenced by seasonal variability of decay time of the inertial oscillations. The ratio of the amplitudes observed above and below pycnocline is controlled by the pycnocline depth, as predicted by a two-layer model. Decay times of the inertial oscillations were found to range between 20 and 80 h, with a maximum recorded in summer. This is consistent with damping imposed on the two-layer sea by the interface and bottom friction, which in turn is heavily dependent on stratification. The contribution of the interface friction to damping varies from less than 5% in summer to about 30% in spring and autumn.