Remotely sensed surface currents in Monterey Bay from shore-based HF radar (Coastal Ocean Dynamics Application Radar)

Near-surface currents in Monterey Bay derived from a network of shore-based HF radars are presented for August–December 1994 and compared with those from April to September 1992. Focus is placed on the low-frequency (2- to 30-day period) motions in the remotely sensed data and on comparison of radar-derived currents with moored current and wind observations, ship-based acoustic Doppler current profiler observations, satellite-based surface temperature imagery, and surface drifter velocities. The radar-derived picture of the late summer mean flow is very similar in the two realizations and is consistent with historical data. Flow is equatorward in the outer part of the bay, poleward in a narrow band nearshore, and very sluggish in the middle of the bay. Low-pass-filtered time series of radar-derived currents are highly correlated with moored current observations and with winds in the outer part of the bay. The vector time series are also coherent across a broad frequency band with currents typically in phase between 1- and 9-m depths and with 1-m currents typically 40°–60° to the right of the wind. Overall, these results confirm the utility of Coastal Ocean Dynamics Applications Radar (CODAR)-type HF radars for the study of coastal surface currents out to ranges ∼50 km from shore, particularly for highly averaged fields. Data variability and comparison with in situ observations for high-frequency (1- to 48-hour period) motions point to the need to better characterize and minimize sources of error in the radar observations.

[1]  Terrence M. Joyce,et al.  On in situ 'calibration' of shipboard ADCPs , 1989 .

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

[3]  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.

[4]  Calvin C. Teague,et al.  Multifrequency HF radar observations of currents and current shears , 1983 .

[5]  Thomas Craig Neal.  Analysis of Monterey Bay CODAR-derived surface currents, March to May 1992 , 1992 .

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

[7]  Duncan B. Ross,et al.  Mesoscale Ocean Surface Current Structure Detected by High-Frequency Radar , 1995 .

[8]  D. Prandle,et al.  Measurement of surface currents in Liverpool Bay by high-frequency radar , 1985, Nature.

[9]  D. Prandle,et al.  A new view of near-shore dynamics based on observations from HF Radar , 1991 .

[10]  Mark Reed,et al.  Field evaluation of satellite-tracked surface drifting buoys in simulating the movement of spilled oil in the marine environment. Final report appendices , 1990 .

[11]  P. R. Bevington,et al.  Data Reduction and Error Analysis for the Physical Sciences , 1969 .

[12]  D. Barrick,et al.  The role of the gravity-wave dispersion relation in HF radar measurements of the sea surface , 1986 .

[13]  G. Griggs.  Nearshore current patterns along the central California coast , 1974 .

[14]  D. Prandle,et al.  Tidal Flow through the Straits of Dover , 1993 .

[15]  D. Chelton,et al.  The Central California Coastal Circulation Study , 1987 .

[16]  D. Ross,et al.  Measurements of Coastal Currents Using a Ship Based VHF Radar System , 1994 .

[17]  D. Chelton.  Seasonal variability of alongshore geostrophic velocity off central California , 1984 .

[18]  Robert L. Smith,et al.  Seasonal cycles of currents, temperatures, winds, and sea level over the northeast pacific continental shelf: 35°N to 48°N , 1987 .

[19]  Donald E. Barrick,et al.  Ocean Surface Currents Mapped by Radar , 1977, Science.

[20]  J. Roughgarden,et al.  Detecting upwelling along the central coast of California during an El Niño year using HF-radar , 1995 .

[21]  James J. Simpson,et al.  The California Current system: The seasonal variability of its physical characteristics , 1987 .

[22]  R. Harrod.  Observations of the California Countercurrent. , 1984 .

[23]  C. S. Nelson.  Wind Stress and Wind Stress Curl over the California Current , 1976 .

[24]  E. T. Petruncio.  Characterization of tidal currents in Monterey Bay from remote and in-situ measurements , 1993 .

[25]  Franklin B. Schwing,et al.  Bifurcated flow from an upwelling center: a cold water source for Monterey Bay , 1994 .

[26]  Laurence C. Breaker,et al.  A Proposed Definition for Vector Correlation in Geophysics: Theory and Application , 1993 .

[27]  Russ E. Davis,et al.  Drifter observations of coastal surface currents during CODE: The method and descriptive view , 1985 .

[28]  Eng-Chong Ha,et al.  Remote sensing of ocean surface current and current shear by HF backscatter radar , 1979 .

[29]  Barbara M. Hickey,et al.  The California current system—hypotheses and facts☆ , 1979 .

[30]  D. Prandle,et al.  Comparison of observed (HF radar) and modelled nearshore velocities , 1989 .

[31]  D. Crombie,et al.  Doppler Spectrum of Sea Echo at 13.56 Mc./s. , 1955, Nature.

[32]  L. C. Breaker,et al.  The circulation of Monterey Bay and related processes , 1989 .

[33]  C. Mooers.  A technique for the cross spectrum analysis of pairs of complex-valued time series, with emphasis on properties of polarized components and rotational invariants , 1973 .

[34]  J. Reid,et al.  Direct measurements of the Davidson Current off central California , 1962 .

[35]  S. Ramp,et al.  Observations of the geostrophic current and water mass characteristics off Point Sur, California, from May 1988 through November 1989 , 1992 .

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

[37]  D. Masson,et al.  A Case Study of Wave–Current Interaction in a Strong Tidal Current , 1996 .

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

[39]  J. G. Field,et al.  Persistent “upwelling shadows” and their influence on zooplankton distributions , 1992 .