Tidal currents in the northwestern Adriatic: High‐frequency radio observations and numerical model predictions

The results of a two-year long deployment of high frequency radars along the Italian coast of the northern Adriatic are analyzed, to characterize the surface tidal currents. M2 and K1 ellipses are aligned with the basin axis and exhibit large eccentricities in the middle of the basin, decreasing toward the Italian coast. Comparisons are made with a 3D finite-element non-linear numerical model of the tides. Complex correlations between modeled and observed tidal currents show a remarkable agreement in the middle of the basin, with magnitudes reaching 0.985 and average phases of -6.4 deg. However the magnitudes drop to 0.5 within 20-30 km from the Italian coast, where the modeled currents amplitudes are underestimated by 2cm/s and the phases lag the observed phases by 60 deg. This shallow region (less than 30-m deep) is characterized by low-salinity water originating at the Po River and laterally sheared coastal flows. The radars may have captured the influence of stratification or mean sheared flows, both absent from the model. The model parameterization of bottom friction may also inadequately represent the effects of real bottom friction on the vertical current shear.

[1]  S. Lentz,et al.  Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE , 2002 .

[2]  Discrete Inverse and State Estimation Problems , 2006 .

[3]  Hans C. Graber,et al.  On the accuracy of HF radar surface current measurements: Intercomparisons with ship‐based sensors , 1997 .

[4]  K. Gurgel,et al.  Wellen Radar (WERA): a new ground-wave HF radar for ocean remote sensing , 1999 .

[5]  R. Weller.  The Relation of Near-Inertial Motions Observed in the Mixed layer During the JASIN (1978) Experiment to the Local Wind Stress and to the Quasi-Geostrophic Flow Field , 1982 .

[6]  Daniel R. Lynch,et al.  Comprehensive coastal circulation model with application to the Gulf of Maine , 1996 .

[7]  P. Poulain,et al.  Unusual upwelling event and current reversal off the Italian Adriatic coast in summer 2003 , 2004 .

[8]  C. Wunsch.  Discrete Inverse and State Estimation Problems: With Geophysical Fluid Applications , 2006 .

[9]  Klaus-Werner Gurgel,et al.  Shipborne measurement of surface current fields by HF radar , 1994, Proceedings of OCEANS'94.

[10]  Mirko Orlić,et al.  The currents and circulation of the Adriatic Sea , 1992 .

[11]  Caskey,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS I . THE BASIC EXPERIMENT , 1962 .

[12]  G. Mellor,et al.  Development of a turbulence closure model for geophysical fluid problems , 1982 .

[13]  B. Cushman-Roisin,et al.  Tidal dynamics in the northern Adriatic Sea , 2000 .

[14]  G. Taylor.  Tidal Oscillations in Gulfs and Rectangular Basins , 1922 .

[15]  A. Rosati,et al.  A Quasi-equilibrium Turbulent Energy Model for Geophysical Flows , 1988 .

[16]  February Bora.  Northern Adriatic Response to a Wintertime Bora Wind Event , 2005 .

[17]  P. Poulain.  Adriatic Sea surface circulation as derived from drifter data between 1990 and 1999 , 2001 .

[18]  Ivica Janeković,et al.  Numerical simulation of the Adriatic Sea principal tidal constituents , 2005 .

[19]  A. Speranza,et al.  Co-oscillating tides in long, narrow bays; the Taylor problem revisited , 1971 .

[20]  I. Janekovic,et al.  The Adriatic Sea M2 and K1 tides by 3D model and data assimilation , 2003 .

[21]  B. Cushman-Roisin,et al.  A 3D finite-element model of the Adriatic tides , 2002 .

[22]  J. Smagorinsky,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS , 1963 .

[23]  Richard P. Signell,et al.  Surface drifter derived circulation in the northern and middle Adriatic Sea: Response to wind regime and season , 2007 .

[24]  E. Kunze.  Near-Inertial Wave Propagation In Geostrophic Shear , 1985 .

[25]  Andrea Bergamasco,et al.  The Dynamics of the Coastal Region of the Northern Adriatic Sea , 1983 .

[26]  B. Lipa,et al.  Least-squares methods for the extraction of surface currents from CODAR crossed-loop data: Application at ARSLOE , 1983, IEEE Journal of Oceanic Engineering.

[27]  Robert H. Stewart,et al.  HF radio measurements of surface currents , 1974 .

[28]  M. Gačić,et al.  Use of the Acoustic Doppler Current Profiler (ADCP) in the study of the circulation of the Adriatic Sea , 2001 .

[29]  P. Poulain,et al.  Northern Adriatic Sea surface circulation and temperature/pigment fields in September and October 1997 , 2001 .

[30]  C. Lozano,et al.  The M(2) tide in the Mediterranean Sea: Dynamic analysis and data assimilation , 1995 .