The Seasonal Variations Of The Northern Pacific Wave Transport And Western Boundary Current

The annual cycle is the most energetic component of the wind stress driving the general ocean circulation. Therefore, it is reasonable to anticipate a prominent annual cycle in the Sverdrup transport. In general, the predicted subtropical transport, integrated across the width of the ocean, will not be zero. To conserve mass at each latitude the transport in the western boundary current (WBC) must exactly compensate for this interior transport. The bulk transport of Kuroshio Current and Gulf Stream together is larger than that of Sverdrup transport. In other words, general pattern is that poleward flowing western boundary currents are much stronger than the return flow in the interior predicted by Sverdrup's theory.Much attention has been focused on the contribution of sea wave to large-scale circulation in recent years. By incorporating this wave-induced Coriolis-Stokes forcing into the momentum balance of the Ekman layer , Polton et al.(2005) pointed out that the Ekman-Stokes model agrees much more reasonably with the observational current profiles than the classical Ekman model. Similar results Were also documented by Lewis & Belcher (2004). Since the wave-induced Coriolis-Stokes forcing significantly modi fied the current profile, it must somehow make contributions to the transports to the ocean.The volume transport of the western boundary current can be also inferred by use of the Sverdrup balance. By employing 44 years reanalysis wind stress data and surface wave data from European Centre for Medium-Range Weather Forecasts (ECWMF) . The averaged seasonal variations in three Sverdrup transports across 32. 50N,30 0N and 27. 50N are estimated. It is found that three Sverdrup transports have almost similar seasonal variation with a maximum in winter and a minimum in summer . In addition, the averaged seasonal variations in three Stokes volume transports are also calculated based on the ECWMF surface wave data, it shows a similar tendency of the annual change in overall Sverdrup transports. The averaged ratio of Stokes transport to Sverdrup transports is about 2 to 3 percent. From these results, it can be inferred that wave transports make a great contribution to Sverdrup transports.