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Ann. Geophys., 22, 1449-1464, 2004
www.ann-geophys.net/22/1449/2004/
© European Geosciences Union 2004
Fundamental Adriatic seiche recorded by current meters
N. Leder1 and M. Orlic2
1Hydrographic Institute of the Republic of Croatia, Zrinsko Frankopanska 161, 21000 Split, Croatia
2Andrija Mohorovičić Geophysical Institute, Faculty of Science, University of Zagreb, Horvatovac bb, 10000 Zagreb, Croatia
Abstract. Currents recorded at two stations positioned at the Adriatic shelf break
between 17 February and 6 March 1989 were considered. They provided the
first evidence of current variability related to the Adriatic-wide seiches.
Current spectra were dominated by a peak at 21.1h – a well-known period of
the fundamental Adriatic mode. Amplitudes of oscillations were considerable,
occasionally greater than 30cm/s. Both along- and cross-basin currents were
recorded, thus signalling the importance of rotational effects. Comparison of
the current data with the sea-level measurements performed simultaneously
along the east Adriatic coast showed that the 21-h currents flowing in the
Adriatic preceded sea levels by a quarter of a cycle, as would be expected
from a simple model of bay seiches. Sea-level amplitudes reached 40cm in
the North Adriatic, thus marking the event as one of the strongest on
record. Seiching was triggered by a suddenly changing sirocco wind, as is
usually the case in the Adriatic. The most important features of the seiche
event were reproduced with a two-dimensional hydrodynamic model of the
Adriatic Sea, forced by the sea-level residuals measured at Otranto and the
air pressure and wind data recorded at Lastovo. The model showed that the
seiche-related currents were relatively strong in the area where the current
measurements were performed and further north – between Zadar and Ancona.
Key words. Oceanography: general (continental shelf processes)
– Oceanography: physical (sea-level variations, currents)
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