Resonantly coupled devastating air-sea event in the east Adriatic: The atmospheric component

Enhanced sea level oscillations with devastating effects occurred on 26/27 June 2003 in the east Adriatic. The phenomenon was recognized as a resonantly coupled air-sea interaction, where the Proudman resonance occurs between the propagating atmospheric pressure disturbance and the open-sea wave. Afterwards the harbor resonance occurs between the propagating air-sea disturbance and the internal harbor oscillation. The time scale of the atmospheric pressure disturbance was 2 – 3 hours with the phase speed of ~ 22 m/s, and its maximum amplitude reached 8 hPa. This study examines the dynamics and predictability of the atmospheric component of the coupled system using the MM5 numerical model.

First, the initiation, amplification and maintenance of the system are examined. The perturbation originates in the Alpine region, where the potentially unstable air in the westerly current lifts over the Alps resulting in convection and wave development. The wave and convective activity apparently couple in a wave-CISK manner and propagate southeastward down the eastern Adriatic coast. The potentially unstable air above the Adriatic additionally amplifies the system along its track. The dissipation of the system occurs after the landfall after about 12 hours of the Mesoscale Convective System (MCS) lifetime.

Second, the performance of the numerical model at the resolution that is similar to operational NWP model resolution is examined. This severe event is highly susceptible to the details of the model configuration, presumably due to the sensitivity in coupling of the wave and MCS. Thus, although the model is able to reproduce and forecast this kind of event at a fairly coarse resolution, the details of the spatial structure, as well as the time of onset, are questionable. In this case, the greatest sensitivity is primarily in the treatment of moist and convective processes.