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| Titel |
Variability of currents in front of the Venice Lagoon, Northern Adriatic Sea |
| VerfasserIn |
S. Cosoli, M. Gačić, A. Mazzoldi |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 26, no. 4 ; Nr. 26, no. 4 (2008-05-13), S.731-746 |
| Datensatznummer |
250016058
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| Publikation (Nr.) |
 copernicus.org/angeo-26-731-2008.pdf |
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| Zusammenfassung |
Time scales and modes of variability of the flow in the water column in the
Northern Adriatic Sea for late summer 2002 are described based on current
record from a single bottom-mounted ADCP in the shallow-water area in front
of the Venice Lagoon.
The time averaged flow was directed 277° E (CCW), roughly aligned with
the coastline, with typical magnitudes in the range 4–6 cm/s and a
limited, not significant clockwise veering with depth. Tidal forcing was
weak and mainly concentrated in the semidiurnal frequency band, with a
barotropic (depth-independent) structure. On a diurnal time scale, tidal
signal was biased by the sea-breeze regime and was characterized by a
clockwise veering with depth according to the Ekman spiral.
A complex EOF analysis on the velocity profile time series extracted two
dominant spatial modes of variability, which explained more than 90% of
the total variance in the current field. More than 78% of the total
variance was accounted for by the first EOF mode, with a barotropic
structure that contained the low-frequency components and the barotropic
tidal signal at semidiurnal and diurnal frequencies. The second mode had a
baroclinic structure with a zero-crossing at mid-depth, which was related
with the response of the water column to the high-frequency wind-driven
diurnal sea breeze variability.
The response of low-passed non-tidal currents to local wind stress was fast
and immediate, with negligible temporal lag up to mid-depth. Currents
vectors were pointing to the right of wind stress, as expected from the
surface Ekman veering, but with angles smaller than the expected ones. A
time lag in the range 10 to 11 h was found below 8 m depth, with current
vectors pointing to the left of wind stress and a counterclockwise veering
towards the bottom. The delay was consistent with the frictional adjustment
time scale describing the dynamics of a frictionally dominated flow in
shallow water, thus suggesting the importance of bottom friction on the
motion over the entire water column. |
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