海南岛东北部风趋上升流之动力过程研究

（Dynamics of wind-driven upwelling off the northeastern coast of Hainan Island）

     观测和海表温度数据再分析均显示了上升流现象频繁发生在海南岛东北部（地形变化处的下游），而这个上升流无法只用沿岸风解释。项目课题四林培根及程鹏等人使用了一个理想地形的模式来说明该上升流的动力学过程。该理想地形根据海南岛东部及东北部岸线和海底地形简化而来。结果显示了这个发生在地形变化处下游的上升流与向岸的跨等深线水体输运有关。垂向积分的动量方程指出该向岸输运主要由正压压强梯度力加强，相反的，被斜压压强梯度力削弱。该正压压强梯度力与涡度方程中的相对涡度的对项想，底应力涡度项和动量通量梯度相关。另一个方面，与上述的斜压压强梯度力有关的过程可以通过位涡平衡来验证。类似于风应力的负位涡贡献，斜压作用的负位涡可以减弱这个与上升流有关的向岸输运。同时，该向岸输运可以被底应力引起的正位涡所加强。除此之外，在较浅的近岸海区，跨等深线的作用力对于该上升流有重要影响。

     Abstract Both observational and reanalysis sea surface temperature data reveal that upwelling occurs frequently off the northeastern coast of Hainan Island (downstream of the change in topography off Tongluo Cape), which cannot be attributed to the along-shelf wind alone. To identify dynamics of the upwelling,we conduct a numerical experiment using an idealized topography that is simplified from the actual topography off the eastern and northeastern coasts of Hainan Island. The result indicates that the upwelling downstream of the change in topography is associated with onshore cross-isobath transport. Analysis of the vertically integrated momentum balance shows that the upwelling-linked onshore transport is primarily intensified by the along-isobath barotropic pressure gradient force (PGT), but is weakened by the alongisobath baroclinic pressure gradient force (PGC). The along-isobath PGT is linked to the advection of relative vorticity, the bottom stress curl and the gradient of momentum flux in vorticity equation. On the other hand, the PGC-related process is diagnosed by potential vorticity (PV) balance. Similar to the negative PV term from wind stress, the negative PV terms of the joint effect of baroclinicity and relief and the baroclinic bottom pressure torque weaken the upwelling-linked onshore transport downstream of the change in topography. The onshore transport is enhanced by the positive PV from bottom stress. In addition, the cross-isobath forces play an important role in upwelling intensification in the shallow nearshore region.

Lin, P., P. Cheng, J. Gan, and J. Hu, 2016. Dynamics of wind‐driven upwelling off the northeastern coast  of Hainan Island. Journal of Geophysical Research: Oceans, 121, 1160-1173, doi:10.1002/2015JC011000.