The decadal variability of the North Pacific gyre oscillation (NPGO) over the 20 th century is examined from a long-term integration of the Simple Ocean Data Assimilation (SODA) reanalysis. The NPGO is reflected by the second dominant pattern of sea surface height (SSH) variability in SODA, with a northsouth dipole structure over the northeast Pacific. SSH anomalies in this region exhibit distinct decadal variability with a significant spectrum peak at approximately 18 years. The upper-ocean heat budget reveals that this dipole structure associated with the NPGO is predominantly due to the anomalous Ekman pumping and Ekman advection induced by the surface wind. The NPGO mode in SODA reanalysis originates from atmosphere stochastic noise (North Pacific Oscillation) which has a meridional dipole pattern but no preferred time scale. The oceanic planetary wave, particularly the advective baroclinic mode, integration of atmospheric stochastic noise leads to a spatial resonance with preferred decadal time scale. The limitation of current study is also discussed.

The South China Sea (SCS) is the largest marginal sea in southeastern Asia and has a far-reaching influence on the regional and global climate (Hu et al., 2000). As a combination of a marginal sea and a deep sea, the SCS has an extended continental shelf in the south and extends deeper than 5,000 m in the central region (Figure 1). It has complicated dynamical features, including large-scale wind-driven gyres, deep thermohaline circulation, as well as energetic mesoscale eddies and turbulence (Huang & Du, 2015). Linking the Pacific and Indian Oceans, the SCS provides water mass exchange carried by numerous straits and is one of the busiest maritime routes in the world. Climatically, the SCS is part of the Indo-Pacific warm pool which acts as an "engine" to drive the global Walker and Hadley cells through strong atmospheric convection (De Deckker, 2016). By providing a slow but more predictable component of the climate system, the SCS is believed to play a significant role in regulating the sea surface temperature (SST) and sea surface salinity (SSS) patterns in the Maritime Continent and adjacent western Pacific and eastern Indian Oceans, directly

Wave streaming is a near-bottom mean current induced by the bottom drag on surface gravity waves. Wave variations include the variations in wave heights, periods, and directions. Here we use numerical simulations to study the effects of wave streaming and wave variations on the circulation that is driven by incident surface waves. Wave streaming induces an inner-shelf Lagrangian overturning circulation, which links the inner shelf with the surf zone. Wave variations cause alongshore-variable wave breaking that produces surf eddies; however, such eddies can be suppressed by wave streaming. Moreover, with passive tracers we show that wave streaming and wave variations together enhance the cross-shelf material transport.