Date of Award
Doctor of Philosophy in Oceanography
The circulation of the northern Adriatic Sea is heavily influenced by repetitive bursts of strong wind forcing, making this area a prototype of a wind-forced, shallow marginal sea. Tides also play an important role, with tidal currents being equal to or stronger than non-storm mean flows. From September 2002 to May 2003, an array of 15 Acoustic Doppler Current Profilers was deployed in the northern Adriatic by the U.S. Naval Research Laboratory and the NATO Undersea Research Centre to measure the circulation and dynamics of this important basin. The first manuscript of this dissertation focuses on circulation observations from a pilot mooring deployed in the Western Adriatic Current (WAC) during 2001 ahead of the main instrumentation array. The second and third manuscripts of the dissertation focus respectively on basin-wide circulations and the vertical structure of tides, making extensive use of data from the main array of moorings deployed from 2002 to 2003.
During the winter of 2001, current variability in the WAC was dominated by four bursts of currents in which flow greatly increased to more than 30 cm/s, three times the depth-averaged mean flow. These bursts followed bora winds, identified by measured winds at the Acqua Alta tower. Correlations between these along-shore currents and simulated wind stress from the COAMPS model had a spatial pattern similar to the bora wind itself. Remote wind stress had stronger correlation with currents than local wind stress showing the importance of basin wide dynamics on local flows.
Bursting of the WAC from October 2002 - April 2003 was used as an index to separate storm and non-storm circulations from the observations of the main basin-wide array. Circulations with storm periods excluded suggest a 2002/2003 seasonal separation consisting of October, December through February, and March through April. Generally in the WAC over 50% of kinetic energy came from vertically-uniform monthly-mean flows. Elsewhere, eddy kinetic energy was stronger than mean kinetic energy with 10%-40% contributions for vertically-uniform monthly-mean flows, 40%- 60% for vertically-uniform monthly-varying flows, and 10%-30% for vertically-varying monthly-varying flows. Mean currents for bora storms indicate enhancement of the Eastern Adriatic Current(EAC)/WAC and double-gyre bifurcation of flow at Istria. Strengthening of both the EAC and WAC also occurs during sirocco storms.
From the main array, most observed tidal current ellipses were nearly reversing, but near the bottom, tidal current ellipses all shortened and broadened, semi-diurnal currents led upper-water column currents, and diurnal tidal current-ellipse orientations rotated counter-clockwise towards the bottom. These match theoretical solutions for a tidally-forced, bottom Ekman layer with vertical eddy viscosity of the form A2 = βz + k. The value of k (average 5 • 10-4 m2 /s) was important in matching tidal orientation and phase changes and a non-zero β (average 3 • 10-4 m/s) was important in matching tidal amplitude changes. Simulations from the Navy Coastal Ocean Model and Quoddy model accurately reproduced the major tidal structure changes with depth, although not as well as optimized theory. Bottom shear stresses were calculated from the models and theory, and theory alone had large components of stress in the cross-axis direction of the northern Adriatic.
Book, Jeffrey W., "NORTHERN ADRIATIC CIRCULATION AND TIDES" (2007). Open Access Dissertations. Paper 1600.