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Bias correction of reanalysis-based wind stress using scatterometer derived equivalent neutral wind has been a common practice in producing the forcing datasets used in recent global ocean model intercomparisons (OMIPs). Here we systematically evaluate the effect of this wind correction procedure on the simulation of the Pacific North Equatorial Countercurrent (NECC) with multiple sets of model experiments. The weak NECC evident in earlier OMIPs employing the Coordinated Ocean-ice Reference Experiments (COREs) forcing dataset persists with the new JRA55-do (Japanese 55-year Reanalysis) forcing dataset. Two factors appear to significantly affect the Pacific NECC in forced ocean simulations: i) the bias correction procedure using QuikSCAT derived winds and ii) whether or not the ocean current is considered in the bulk formula. In the forced ocean simulations, the QuikSCAT correction weakens the averaged NECC transports by about 60%. Taking the ocean currents into account in the bulk formula may weaken the averaged NECC transports by about 26%–30%. Under the current OMIP protocol the above two procedures are used together to force the ocean model resulting in a double-counting of ocean surface current feedback on wind stress because the QuikSCAT estimates the equivalent 10-m neutral winds relative to surface current. We further systematically verify and investigate the impacts of this double-counting of the ocean surface currents on the modeled Pacific NECC using offline linear Sverdrup transport analysis, in which the observational data of vector wind and surface current are used to calculate the surface wind stress. It shows that including the ocean current in the bulk formula may reduce the zonal Sverdrup transport (ZST) by about 6.6 Sv (33%) and the further double-counting of the ocean current leads to an additional reduction of 6.4 Sv (48%). Next, using "perfect model" experiments with output from a coupled ocean–atmosphere model we further identify that the double-counting of current feedback in the bulk formula results in approximately 21% weakened volume transport. The built-in nonlinear processes in the model, such as the advection and friction terms, may partly damp the reduction due to the double-counting of the ocean current. However, the double-counting bias can only explain 26%–30% of the Pacific NECC simulation bias and the other part of the bias, around 30%, caused by the correction with QuikSCAT has not been explained. We speculate that this part may be explained by the retrieval biases in QuikSCAT wind data and the use of annual mean climatological wind adjustment factors. • The weak Pacific NECC remains in ocean models even if JRA55-do forcing data is used in OMIP-2. • The wind correction with QuikSCAT is the main factor affecting the Pacific NECC simulations. • The surface ocean current is counted-twice incorrectly when calculating the wind stress in ocean models. [ABSTRACT FROM AUTHOR]

The generation of non-linear internal waves evident in two Synthetic Aperture Radar (SAR) images of the Gulf of Oman has been studied. The internal waves form packets, propagating towards the Musandam Peninsula from the eastern shelf-edge, travelling right up to the coast. The internal waves on the shelf have the classic appearance of rank ordered non-linear waves that depress the pycnocline. The images suggest a tidal generation mechanism. Under this assumption, estimates of the phase speeds of the waves were derived and found to vary from 0.5 m s−1 near the coast to 0.7 m s−1 on the shelf. The possible generation of the internal waves at the Gulf of Oman shelf-break has been investigated using numerical models. A 2D barotropic tidal model has been used to assess the tidal flux across the continental slope in the region of interest. The model indicates that tidal flow at the shelf-edge is mainly across-slope. The tidal flux information is used to drive a two-layer non-linear internal tide model, which simulates the internal tide along a vertical slice perpendicular to the shelf-edge. Numerical results for a tidal flux corresponding to the spring tide (corresponding to one of the SAR images) indicate that this is strong enough to produce high-frequency waves for all layer depths considered. It is found that for the weaker modelled value of tidal flux corresponding to the time of the other SAR image, using two-layer parameters derived from a climatological density profile, the forcing is just too weak to force high-frequency internal waves. However, a sensitivity study investigating the effects of different layer depths suggests that a reduction in the top layer thickness by 10 m is sufficient to produce waves similar to those observed. The model predicts internal waves of depression with peak to trough amplitudes up to 25 m, surface currents up to 0.6 m s−1, and strain rates of O(10−3 s−1). The phase speeds of the internal waves from the model (0.9 m s−1) are slightly higher than those observed, possibly due to approximations of smooth bathymetry and climatological density profiles used in the model, or due to the approximate nature of inferring observed phase speeds from two SAR images from different years. As the qualitative features of the observed internal waves are reproduced by the internal tide model, it is concluded that tidal flow over the shelf-edge is the likely generation mechanism for the internal waves imaged by SAR. [Copyright &y& Elsevier]