Wave‐current interaction near the Gulf Stream during the Surface Wave Dynamics Experiment

Abstract

This paper presents a case study on the wave-current interaction near the local curvature of a Gulf Stream meander. The wave data were obtained from in situ measurements by a pitch-roll discus buoy during the Surface Wave Dynamics Experiment (SWA-DE) conducted off Wallops Island, Virginia, from October 1990 to March 1991. Owing to the advection of the Gulf Stream by the semidiurnal tide, the discus buoy was alternately located outside and inside the Gulf Stream. The directional wave measurements from the buoy show the changes in wave direction, wave energy, and directional spreading when waves encountered the current in the Gulf Stream meanders. A wave refraction model, using the ray-tracing method with an estimated Gulf Stream velocity field and meandering condition, was used to simulate wave refraction patterns and to estimate wave parameters at relative locations corresponding to buoy measurements. The numerical simulation shows that a focusing zone of wave rays was formed near the boundary and behind the crest of a simulated Gulf Stream meander. The focusing of wave rays causes changes in wave direction, increases in wave energy, and decreases in wave directional spreading, which are in good agreement with the results from the buoy measurements. 1. Introduction When a surface wave train encounters a variable current, an interchange of momentum and energy occurs which can be quite strong. The wave refraction by the shear current at an oceanic from can significantly change wave direction, wavelength, and wave energy [Johnson, 1947; Kenyon, 1971]. Recently, Irvine [1987] showed that the effect of the current meandering, or the local curvature of the current, can further complicate the wave refraction pattern. Mapp et al. [1985], Irvine [1987], and Irvine and Tilley [1988] suggested that unexpected giant waves [Draper, 1964; Schumann, 1976] are caused by local focusing of swell refraction in a meandering oceanic from. Liu et al. [1989] presented a case study of wave-current interaction near an oceanic front, which examined the effects of meandering on waves propagating across the frontal current using directional wave data obtained by NASA airborne radar and numerical model simulations. Most previous studies on wave-current interaction in an oceanic from relied on numerical model simulations with limited field measurements that were obtained mainly by means of remote sensing [Hayes, 1980; McClain et al.McLeish and Ross, 1985; Mathiesen, 1987; Holthuijsen and Tolman, 1991]. Sheres et al. [1985, 1987] inferred the strength of a linear shear feature in a coastal current system on the basis of wave refraction observed in aerial photo-Weller, R.A., M. A. Donelan, M. G. Briseoe, and N. E. Huang, Riding the crest: A tale of two wave experiments, Bull.

Current-Induced Modulation of the Ocean Wave Spectrum and the Role of Nonlinear Energy Transfer

“…In general, changes in wave characteristics are attributed to physical processes of wave refraction and/or straining (Holthuijsen and Tolman 1991) caused by the horizontal shear current. Recent studies using spaceborne altimeter data have indicated that strong ocean currents, such as the Kuroshio of the Pacific Ocean, exert a significant influence on wave characteristics (Hwang 2005); similar observations have been reported for a wide range of temporal and spatial scales (Tolman 1991;Wang et al 1994;Masson 1996). Moreover, wave-current interactions may generate so-called freak waves of extreme size (e.g., White and Fornberg 1998), as abnormal waves have been observed repeatedly in areas with strong currents (e.g., Lavrenov 1998).…”

A comparative study of wave‐current interactions over the eastern Canadian shelf under severe weather conditions using a coupled wave‐circulation model

“…By using a wave refraction model, Wang et al . [] showed that the focusing of wave rays by the Gulf Stream meander causes changes in wave direction/energy and directional spreading observed by in situ measurements. Liu et al .…”

“…Holthuijsen and Tolman [1991] found that the current-induced wave refraction due to the strong current shear of the Gulf Stream could induce a considerable variation on wave heights. By using a wave refraction model, Wang et al [1994] showed that the focusing of wave rays by the Gulf Stream meander causes changes in wave direction/energy and directional spreading observed by in situ measurements. Liu et al [1994] also showed that mesoscale eddies can be detected from the synthetic aperture radar images via the influence of eddy currents on the surface wave fields.…”

A perturbation model of radiometric manifestations of oceanic currents

“…Significant insights have been obtained by theoretical analysis of waves on currents with velocity depending on only one coordinate [ Longuet‐Higgins and Stewart , 1960, 1961; McKee , 1974; Basovich and Talanov , 1977; Hughes , 1978; Basovich et al , 1987; Thompson et al , 1988; Gotwols et al , 1988; Trulsen et al , 1990; Maltseva et al , 1995; van der Kooij et al , 1995]. Direct numerical integration of equations governing wave train trajectories and wave action balance has been used when simulating surface wave interaction with currents variable in two dimensions [ Irvine and Tilley , 1988; Liu et al , 1989; Brissette et al , 1993; Wang et al , 1994].…”