Surface current variability and wind influence in the northeastern Adriatic Sea as observed from high-frequency (HF) radar measurements

Abstract A network of HF radars operated in the northeastern Adriatic Sea in the period September 2007 to August 2008. Surface currents were collected with the purpose of studying the temporal and spatial modes of surface circulation in the area. Their dependence on local wind forcing was investigated using wind records from coastal stations and the mesoscale meteorological model ALADIN/HR. EOF decomposition, spectral and tidal analyses, and time-lagged correlation extracted the dominant features in the area and their time scales. The time-averaged flow presented a cyclonic circulation pattern with relatively weak currents and standard deviations comparable to average values. Three dominant current patterns were extracted by the EOF analysis, which accounted for about 70% of total variance. In the region, wind was the major source of current variability over a wide portion of frequencies, whereas tidal forcing was weak and limited to the semidiurnal and diurnal frequencies, representing 10%–20% of the total variance. The response to wind forcing was immediate with veering angles consistent with Ekman dynamics in the majority of the area. Coherence analyses revealed strong correlation within the sub-tidal and diurnal bands, the latter related to diurnal sea-breezes variability. The seasonal variability of the inertial motions was also observed in the area.

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

[2]  Craig M. Lee,et al.  A climatology of the northern Adriatic Sea's response to bora and river forcing , 2007 .

[3]  W. Large,et al.  Open Ocean Momentum Flux Measurements in Moderate to Strong Winds , 1981 .

[4]  L. Cavaleri,et al.  ADCP observations of the western Adriatic slope current during winter of 2001 , 2005 .

[5]  Aniello Russo,et al.  The Adriatic Sea general circulation. Part I: Air-sea interactions and water mass structure , 1997 .

[6]  M. Orlić,et al.  Istrian coastal countercurrent in the year 1997 , 2003 .

[7]  Paul J. Martin,et al.  Modeling the northern Adriatic double-gyre response to intense bora wind: A revisit , 2007 .

[8]  Paul J. Martin,et al.  Simulation of the northern Adriatic circulation during winter 2003 , 2007 .

[9]  Hans C. Graber,et al.  Introduction to High-Frequency Radar: Reality and Myth , 1997 .

[10]  D P Atwater,et al.  Temporal error analysis for compact cross-loop direction-finding HF radar , 2010, OCEANS 2010 MTS/IEEE SEATTLE.

[11]  Jeffrey D. Paduan,et al.  Remotely sensed surface currents in Monterey Bay from shore-based HF radar (Coastal Ocean Dynamics Application Radar) , 1996 .

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

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

[14]  Hans C. Graber,et al.  VALIDATION OF HF RADAR MEASUREMENTS , 1997 .

[15]  J. Beckers,et al.  Ensemble perturbation smoother for optimizing tidal boundary conditions by assimilation of High-Frequency radar surface currents - application to the German Bight , 2009 .

[16]  Libe Washburn,et al.  Evaluating Radial Current Measurements from CODAR High-Frequency Radars with Moored Current Meters , 2004 .

[17]  Mirko Orlić,et al.  Response of the Adriatic Sea to the bora and sirocco forcing , 1994 .

[18]  Simone Cosoli,et al.  Variability of currents in front of the Venice Lagoon, Northern Adriatic Sea , 2008 .

[19]  Benoit Cushman-Roisin,et al.  Mesoscale‐resolving simulations of summer and winter bora events in the Adriatic Sea , 2007 .

[20]  M. Orlić,et al.  Istrian Coastal Countercurrent and its year-to-year variability , 2000 .

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

[22]  M. Orlić,et al.  Seasonal variability of inertial oscillations in the Northern Adriatic , 1995 .

[23]  Aniello Russo,et al.  The Adriatic Sea General Circulation. Part II: Baroclinic Circulation Structure , 1997 .

[24]  Joseph Gonella,et al.  A rotary-component method for analysing meteorological and oceanographic vector time series , 1972 .

[25]  H. Graber,et al.  An EOF analysis of HF Doppler radar current measurements of the Chesapeake Bay buoyant outflow , 1999 .

[26]  Klaus-Werner Gurgel,et al.  Tidal currents in the northwestern Adriatic: High‐frequency radio observations and numerical model predictions , 2007 .

[27]  S. DiMarco,et al.  Seasonal variation of wind‐driven diurnal current cycling on the Texas‐Louisiana Continental Shelf , 2000 .

[28]  Laurence C. Breaker,et al.  The Application of a Technique for Vector Correlation to Problems in Meteorology and Oceanography , 1994 .

[29]  Andrea Bergamasco,et al.  Baroclinic Response of the Adriatic Sea to an Episode of Bora Wind , 1996 .

[30]  George O. Marmorino,et al.  Empirical Orthogonal Function Analysis of Ocean Surface Currents Using Complex and Real-Vector Methods* , 1998 .

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

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

[33]  David M. Kaplan,et al.  HF radar observations of surface circulation off Bodega Bay (northern California, USA) , 2005 .

[34]  William J. Emery,et al.  Data Analysis Methods in Physical Oceanography , 1998 .

[35]  M. Orlić,et al.  Occurrence of the Istrian Coastal Countercurrent in 2000, a year with a mucilage event , 2001 .

[36]  Vlad Isakov,et al.  A case study of bora-driven flow and density changes on the adriatic shelf (January 1987) , 2001 .

[37]  Scott Glenn,et al.  Improving HF Radar Surface Current Measurements with Measured Antenna Beam Patterns , 2003 .

[38]  S. Marinetti,et al.  HF radar observations in the northern Adriatic: surface current field in front of the Venetian Lagoon , 2004 .

[39]  Robert Tibshirani,et al.  Bootstrap Methods for Standard Errors, Confidence Intervals, and Other Measures of Statistical Accuracy , 1986 .

[40]  R. Signell,et al.  Coupled ocean-atmosphere nested modeling of the Adriatic Sea during winter and spring 2001 , 2003 .

[41]  I. Vilibić,et al.  Surface current patterns in the northern Adriatic extracted from high‐frequency radar data using self‐organizing map analysis , 2011 .

[42]  Julie Pullen,et al.  Bora event variability and the role of air‐sea feedback , 2007 .

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

[44]  Martina Tudor,et al.  Use of high-resolution dynamical adaptation in operational suite and research impact studies , 2004 .

[45]  Pierre-Marie Poulain,et al.  Drifter observations of surface circulation in the Adriatic Sea between December 1994 and March 1996 , 1999 .

[46]  P. K. Kundu,et al.  Ekman Veering Observed near the Ocean Bottom , 1976 .

[47]  A. Mazzoldi,et al.  Comparison between HF radar current data and moored ADCP currentmeter , 2005 .

[48]  R. Signell,et al.  Measurements of storm and nonstorm circulation in the northern Adriatic: October 2002 Through April 2003 , 2007 .

[49]  B. Sanderson.  Structure of an eddy measured with drifters , 1995 .

[50]  Simone Cosoli,et al.  Validation of Surface Current Measurements in the Northern Adriatic Sea from High-Frequency Radars , 2010 .

[51]  K. Schroeder,et al.  Evidence of a dense water vein along the Libyan continental margin , 2008 .

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

[53]  J. Paduan,et al.  Surface current patterns in front of the Venice Lagoon , 2009 .