High-frequency atmospherically-induced oscillations in the middle Adriatic coastal area

Temporal and spatial characteristics of the resonant coupling between travelling air pressure disturbances and the middle Adriatic coastal waters are examined using a barotropic numerical model for a one year period (July 2000–July 2001). The model is forced by the travelling air pressure disturbances reconstructed from the 2-min resolution air pressure series measured at Split. Six experiments for the studied period are performed, in order to analyse the influence of the speed and disturbance direction on the resonant coupling. The first group of three experiments uses variable disturbance direction, whereas in the second three, a constant direction is employed during the whole experiment. Disturbance direction for the first group of experiments is computed from the 500-mb geopotential data provided by European Center for Medium Range Weather Forecast (ECMWF), as it is found that all of the past extreme events are correlated with them. Each experiment, with variable and constant disturbance direction, is repeated with three different constant values of 10, 20 and 30 m/s for the disturbance speed. The model verification on the Split sea level data reveals that the model reproduces most of the events but also overestimates/underestimates some of them and creates some false events due to the rigid assumption of a constant disturbance speed. The best agreement with data is obtained in the model runs assuming a disturbance speed of 20 m/s. A number of trapped and edge waves have been modelled at the constrictions and along the coast, in particular on a shoal that lies off Split perpendicular to the channel axis. The importance of the disturbance direction to the energy content is highlighted, particularly close to the shore, where the difference may be significant at 2–3 times on average, up to 30 cm in maximum amplitude

Bora-induced currents corresponding to different synoptic conditions above the Adriatic

International audienceThe Bora wind field is characterised by strong vorticity and divergence. Several numerical experiments, in which an oceanographic model was forced with northeasterly winds having climatological alongshore variability, were performed in order to study the influence of spatial variability in the bora wind field on the surface currents in the northern Adriatic. Numerical model results showed that during bora episodes with lower speeds and fast offshore decay surface currents along transect Rovinj - Po River are predominantly in the downwind direction. On the other hand, during bora episodes with strong intensity and slow offshore decay, a cyclonic gyre due to the pronounced bora alongshore variability is formed in the northernmost part of the Adriatic Sea and the studied transect is influenced by the counter currents. Moreover, bora having a high speed and a short offshore range produces the same effect in the eastern part of the Rovinj - Po River transect as low-speed bora characterised by slow offshore decay. Eulerian current measurements performed in the northern Adriatic during bora episodes characterised by different synoptic conditions supported the numerical model findings. Surface currents during the bora episode of 8-11 February 1984 were directed downwind, whereas during the episode of 12-19 February 1984 they were directed upwind. The first episode was characterised by a deep bora layer with cyclonic activity over the western Mediterranean and Genoa Bay, whereas the second one was accompanied by temperature inversion and a southwesterly tropospheric wind above a shallow bora layer. According to the hydraulic theory developed by Smith (1985), an observed descent of isentropes during the second bora episode led to the stronger acceleration in the bora layer and its larger offshore extent. Different offshore bora decays during studied events were confirmed by a comparison of the wind data originating from the meteorological stations positioned on the opposite Adriatic coasts

Coastal sea responses to atmospheric forcings at two different resolutions

We investigated coastal sea responses to three, multi-day strong wind episodes that occurred in the middle Adriatic during the Target Operational Period (TOP) of the European COastal sea OPerational observing and forecasting system (ECOOP) project. A high-resolution oceanographic model (1 km horizontal, 16 vertical layers) based on the modified Princeton Ocean Model (POM) was applied to a highly complex domain located in the coastal area of the eastern Adriatic Sea. The oceanographic model was nested into the Adriatic REGional model (AREG-2) covering the entire Adriatic Sea. Meteorological forcing was prepared by two atmospheric models. The coarser model was the European Centre for Medium-range Weather Forecast model (ECMWF, with horizontal and temporal resolutions of 0.25 and 6 h, respectively), and the finer one was the Aire Limit´ee Adaptation dynamique D´eveloppement InterNational model (ALADIN, with horizontal and temporal resolutions of 8 km and 3 h, respectively, and winds dynamically adapted to a horizontal resolution of 2 km). The results show that smallscale atmospheric features, which arise due to the orographically complex mainland and the number of islands and were not reproduced by the coarser atmospheric model, substantially affected surface currents, mass transports, sea surface temperature (SST) and surface salinity in the coastal area during strong Bora. For strong Sirocco, the atmospheric model’s resolution was important for currents on the lee sides of islands.Published521–532JCR Journalope