An analysis of HF radar measured surface currents to determine tidal, wind‐forced, and seasonal circulation in the Gulf of the Farallones, California, United States

Abstract

[1] A complete year of hourly 3 km resolution high-frequency radar measured surface currents covering the Gulf of the Farallones were analyzed with the following three primary objectives: (1) describe the seasonal surface circulation, (2) identify tidal currents, and (3) determine the influence of wind forcing. Three predominant seasonal circulation regimes were identified: relaxation, storm, and upwelling. The relaxation period exhibited mean poleward flow over the slope, variable equatorward flow over the shelf, and cyclonic and anticyclonic eddies south of Pt. Reyes. The storm period mean flow was variable and exhibited evidence of coastally trapped buoyancy flow from the mouth of the San Francisco Bay. The upwelling period exhibited equatorward flow throughout the gulf with regions of intensified flow at the northern and southern regions over the slope. The tidal variance ranged from 4 to 60%, was highest around the mouth of the Bay, decreased past the shelf, and its spatial pattern reflected the combined influence of the K 1 and M 2 tidal current amplitudes. K 1 ellipses typically rotated clockwise throughout the gulf and decreased in amplitude past the shelf. M 2 ellipses were comparably more variable in orientation and magnitude. Harmonic "tidal" analyses of buoy wind data over 4 month time periods showed significant K 1 amplitudes which did not appear when the analysis was done for the entire year. This indicates that harmonic tidal analyses on surface currents are probably more effective at disassociating diurnal sea breeze driven currents when performed over long periods of time such as a year.Citation: Gough, M. K., N. Garfield, and E. McPhee-Shaw (2010), An analysis of HF radar measured surface currents to determine tidal, wind-forced, and seasonal circulation in the

Mapping the U.S. West Coast surface circulation: A multiyear analysis of high-frequency radar observations

“…The spectra of surface vector currents off the USWC are characterized by variance peaks in the low‐frequency band [∣ σ ∣ ≤ 0.4 cycles per day (cpd)], in two bands centered at diurnal and semidiurnal frequencies [tides ( K 1 , M 2 , and S 2 ), diurnal wind ( S 1 ) and its harmonics], and at the inertial frequency ( f c = 1.06 to 1.49 cpd for 32°N to 48°N) (Figures 1b and 7b) [e.g., Paduan and Rosenfeld , 1996; Kosro , 2005; Beckenbach and Washburn , 2004; Kaplan et al , 2005; Gough et al , 2010; Kim et al , 2010a].…”

Dynamics and sea state in the Gulf of Naples: potential use of high-frequency radar data in an operational oceanographic context

“…The highfrequency component primarily includes the sea breeze (Uttieri et al 2011;Cianelli et al 2013) and the inertial response (Kaplan et al 2005), whereas the low-frequency component ranges from scales of a few days associated with changes in the wind field (related to local variation and atmospheric mesoscale variability; see Gough et al 2010) up to the residual and seasonal circulation of the investigated area (Prandle & Player 1993;Sentchev et al 2009;Muller et al 2010;Kim et al 2011). Wind-forced dynamics spread over a wide range of temporal scales and HFRs have proven to be very effective in resolving nearly all of them.…”

Quality Assessment Techniques Applied to Surface Radial Velocity Maps Obtained from High-Frequency Radars

“…There are several coastal regions where M 2 internal tides have been identified by HFR observations, including Oregon (e.g., Kurapov et al 2003); Bodega Bay (e.g., Kaplan et al 2005), off San Francisco Bay (e.g., Gough et al 2010), and Monterey Bay (e.g., Paduan and Cook 1997;Rosenfeld et al 2009) in California;and Hawaii (e.g., Zaron et al 2009;Chavanne et al 2010a). …”