Anisotropic Response of Surface Currents to the Wind in a Coastal Region

Abstract

Analysis of coastal surface currents measured off the coast of San Diego for two years suggests an anisotropic and asymmetric response to the wind, probably as a result of bottom/coastline boundary effects, including pressure gradients. In a linear regression, the statistically estimated anisotropic response explains approximately 20% more surface current variance than an isotropic wind-ocean response model. After steady wind forcing for three days, the isotropic surface current response veers 428 6 28 to the right of the wind regardless of wind direction, whereas the anisotropic analysis suggests that the upcoast (onshore) wind stress generates surface currents with 108 6 48 (718 6 38) to the right of the wind direction. The anisotropic response thus reflects the dominance of alongshore currents in this coastal region. Both analyses yield winddriven currents with 3%-5% of the wind speed, as expected. In addition, nonlinear isotropic and anisotropic response functions are considered, and the asymmetric current responses to the wind are examined. These results provide a comprehensive statistical model of the wind-driven currents in the coastal region, which has not been well identified in previous field studies, but is qualitatively consistent with descriptions of the current response in coastal ocean models.

Variability in the air–sea interaction patterns and timescales within the south-eastern Bay of Biscay, as observed by HF radar data

“…This is in agreement with the results of Kirincich et al (2005) on the mid-shelf off central Oregon, Kim et al (2009) in waters of San Diego and Ardhuin et al (2009) on the western coast of France. In particular, Kim et al (2009) have reported anisotropic and asymmetric coastal surface current response to the wind in relation to the bottom and coastline boundary effects. The deflection angle also varies seasonally, being larger in summer than in winter.…”

“…Yoshikawa et al (2007) identified a current profile corresponding to the Ekman spiral in the Tsushima Strait (based on observations from current profilers and HF radar) using EOF analysis. The wind impulse response and transfer functions have been widely discussed with HF radar currents in California and interpreted according to the Ekman theory by Kim et al (2009Kim et al ( , 2010. Zhao et al (2011) also attributed the subtidal flow to Ekman windinduced dynamics in waters of Qingdao (China).…”

The green ribbon: Multiscale physical control of phytoplankton productivity and community structure over a narrow continental shelf

“…The correlation between the vertical shear in the alongshore currents and the alongshore windstress is dominated by currents in the surface-most ADCP bins (, 5 m). Recent calculations made from high-frequency radar-derived surface currents and local winds in the vicinity of the study site demonstrate that the local wind drives a surface current response that is a combination of direct forcing and geostrophically balanced pressure gradients due to upwelling-or downwelling-favorable winds (Kim et al 2009). It is possible that the lack of near-surface resolution in previous studies (Winant and Olson 1976;Lentz and Winant 1986) obscured the forcing relationship between the local winds and the surface currents.…”

Tidal and Sub-tidal Current Characteristics in the Central part of Chunsu Bay, Yellow Sea, Korea during the Summer Season

“…잔차류의 동-서 성분 평균은 표층부터 저층까지 -0.07~-0.31 cm/sec (Bye, 1965;Churchill and Csanady, 1983;Wu, 1983;Weber, 1983;Kim, 2009 (Fig. 3), 만의 북부에서 유입된 담수는 표층을 통해 북쪽에서 남쪽으로 평균 5~15 cm/sec의 속도로 이동했다 (정 등, 2011a, 2011bJung et al, 2011;정 등, 2012b, 2012c.…”