A climatological study of the unidodal free oscillation in the Adriatic Sea

Abstract

      The paper examines uninodal free oscillation of the Adriatic Sea and investigates its behaviur in the climatological sense. Analysis is made on the hourly sea level data collected at four tide gauge stations situated on the east Adriatic coast, while the examined period is 1986-1997. Residual sea levels are calculated by subtracting the predicted tide from the original series. Uninodal seiche is extracted from the residuals using band-pass filter, furthermore, the filtered amplitudes (envelopes) are calculated. The annual mean seiche amplitude does not vary from year to year whereas annual maximum at Rovinj is always higher than 17 cm. The largest amplitudes occur in October-March period, however, the seiche can appear strongly, but very rarely, also during summer. The annual maximum of the seiche amplitude appears in about 40 % of cases in the northern Adriatic coupled together with the annual maximum of the residual sea level. Mean amplitude ratios between Bakar and Rovinj, Split and Rovinj and Dubrovnik and Rovinj stations are calculated to be of 0.86 ± 0.03 cm, 0.48 ± 0.03 cm and 0.23 ± 0.02 cm, respectively. The decay time calculated from the strongest seiche episode is estimated at 81 ± 19 h. The amplitude of the seiche at Rovinj is estimated to be of 53 cm for the return period of 100 years, consequently, the seiche coupled with the high tide may cause a significant damage along the northern Adriatic coast.