The spatial‐temporal variability of air‐sea momentum fluxes observed at a tidal inlet

Abstract

Coastal waters are an aerodynamically unique environment that has been little explored from an air-sea interaction point of view. Consequently, most studies must assume that open ocean-derived parameterizations of the air-sea momentum flux are representative of the nearshore wind forcing. Observations made at the New River Inlet in North Carolina, during the Riverine and Estuarine Transport experiment (RIVET), were used to evaluate the suitability of wind speed-dependent, wind stress parameterizations in coastal waters. As part of the field campaign, a small, agile research vessel was deployed to make high-resolution wind velocity measurements in and around the tidal inlet. The eddy covariance method was employed to recover direct estimates of the 10 m neutral atmospheric drag coefficient from the three-dimensional winds. Observations of wind stress angle, near-surface currents, and heat flux were used to analyze the cross-shore variability of wind stress steering off the mean wind azimuth. In general, for onshore winds above 5 m/s, the drag coefficient was observed to be two and a half times the predicted open ocean value. Significant wind stress steering is observed within 2 km of the inlet mouth, which is observed to be correlated with the horizontal current shear. Other mechanisms such as the reduction in wave celerity or depth-limited breaking could also play a role. It was determined that outside the influence of these typical coastal processes, the open ocean parameterizations generally represent the wind stress field. The nearshore stress variability has significant implications for observations and simulations of coastal transport, circulation, mixing, and general surf-zone dynamics.

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

“…Although Eskasoni Reserve is adjacent to the Bras d'Or Lake, the local topography and bathymetry is different near the reserve and in Whycocomagh Bay. Thus, it is likely that the wind speed and momentum stress at the airwater interface differs at Whycocomagh Bay compared to Eskasoni Reserve (Ortiz-Suslow et al, 2015).…”

Increased Aerodynamic Roughness Owing to Surfzone Foam

“…Continuous measurements for four weeks in May-June 2016 were divided into 15-min blocks for analysis. The analysis for computing momentum fluxes and procedures for quality controlling the data is given in Aubinet et al (2012), which is similar to that described by Shabani et al (2014) and Ortiz-Suslow et al (2015).…”

Water surface slope spectra in nearshore and river mouth environments

“…Generally, intervals between 15 and 30 minutes are used in deep water conditions, where spatial homogeneity can be assumed over the sampling interval. A five-minute window was chosen for this study [11] due to the combination of the spatial heterogeneity of the wave and wind stress field observed at MCR and the area covered by the vessel (∼  m per interval). It is expected that the short surface waves respond most directly to the smaller-scale eddies in the atmospheric boundary layer, which are fully resolved over this time frame.…”