engleski

The Bakar Bay seiches and their relationship with the atmospheric processes

Large-amplitude seiches (up to 40 cm) were recorded at a tide-gauge inside Bakar Bay during 19 – 21 August 2006. They were analysed using available tide-gauge and meteorological (air pressure and wind, vertical sounding) data. Sea level and air pressure spectra showed simultaneous increase of energy at the periods containing those of both Bakar Bay (about 20 min) and Rijeka Bay (ca. 2 h) seiches. The propagation speed and direction as well as the horizontal span of the four pronounced pressure disturbances, favourable for the coupling with the Rijeka Bay waters via the Proudman resonance, were determined. It is argued that only short atmospheric pressure disturbances may generate significant barotropic sea waves in a small basin such as Rijeka Bay ; once generated they are amplified when hitting Bakar Bay due to the harbour resonance. Furthermore, examination of synoptic situation and upper-air soundings revealed a presence of dynamically unstable layer at the height of around 2000 m, being also the height of temperature inversion that developed as a consequence of an advection of warm African air from the south-east. During afternoon hours of 19 August 2006 wind speed in this layer was close to the estimated speed of propagation of the air pressure disturbances, which together with dynamical instability made conditions favourable for long distance propagation and trapping of atmospheric gravity waves.

seiches ; air pressure oscillations ; air-sea coupling ; Proudman resonance ; harbour resonance ; Adriatic Sea

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