Ekman bottom layer

The surface circulation of the western basin apparently remains anticyclonic, and the deep circulation cyclonic, under the predominant winds. As far as the relatively fast surface currents are concerned, the transversal spatial scale of today s sea is too small for the Coriollis force to be significant, so that the direct wind drag matters rather than the Ekman transport. On the other hand, the bottom layer circulation seems to immediately follow the sea surface slopes in the classic barotropic manner, so the Coriollis force is still effective for the slower, near-bottom currents. 

The induced surface flow also gives rise to secondary bulk fluid motion, in the same way that bulk meridional vortices are generated in a fluid trapped between rotating and stationary disks in Batchelor flows [19], as depicted in Fig. 12. In this flow recirculation mode, particles dispersed in the flow are convected to the bottom by the bulk meridional recirculation. However, due to the inward radial velocity in the Ekman boundary layer (see Fig. 13), the particles begin to swirl in a helical-like manner toward the center of the base [19]. Although the flow recirculates back up a central spinal coluirm, the gravitational... 

Sharpies (1997) made observations on the intrusion of subtropical water into the coastal zone of northeast New Zealand from late winter to midsummer 1994-1995, 1 year after the Karenia spp. bloom. He showed that the intrusion of subtropical water into the gulf was associated with high salinity nutrient depleted surface layers and near bottom waters with high nitrate N levels (3-5 mmol/m ). Southeasterly winds that occurred in late-November and mid-December 1992, prior to the bloom, are consistent with the hypothesis that Ekman transport effects on the East Auckland current induced the movement of a subtropical water mass, possibly carrying an established dinoflagellate community, into the Hauraki Gulf in late-December 1992. 

The thermal structure reveals the existence of a barrier layer in the SCS. The barrier layer usually weakens the cooling effect entrained at the bottom of the mixed layer. There are barrier layers in both the NSCS and SSCS, but they are thinner than that in the western equatorial Pacific. A barrier layer in the SSCS has a seasonal variation, and its depth has a positive correlation with temperature in the mixed layer. In addition, the barrier layer often exists in summer and autumn. The structure of the barrier layer in the SSCS is significantly modulated by the wind field, as well as by development of the mixed layer. In summer, relatively fresh water in the upper layer in the SSCS piles up in the southeast SCS because of the combined action of southeastward Ekman transport and downwelling in the eastern SCS. The high temperature water at the bottom of the mixed layer remains in a thermally uniform layer after separating from the mixed layer. The deepest barrier layer lies in the southeastern SCS, at about 30 m depth. The location of the thickest barrier layer almost overlaps the SCS Warm Water, which suggests that the heat barrier effect may stimulate the development of the SCS Warm Water. 

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