How ENSO influence the Luzon Strait transport 汇报人：叶瑞杰 专业年级： 2016 级物理海洋博士

Content 1. Background 2. ENSO effects on LST 3. Conclusion 4. Problems

1. Background-->Western boundary current system (Hu et al., 2015) After impinging upon the Philippine coast the NEC bifurcates into the northward- flowing Kuroshio and the southward- flowing Mindanao Current. (Qiu et al., 2015)

1. Background-->Luzon Strait Transport (LST) Structure (Zhu et al., 2016) Winter Summer LST is the total transport through the Luzon Strait, which is essentially westward.

1. Background--> Meridional overturning circulation of SCS (Gan et al., 2016) (Zhu et al., 2016) Upper layer Basin-scale cyclonic circulation Intermediate layer Basin-scale anticyclonic circulation Deep layer cyclonic circulation

1. Background--> What factors influence LST ? Surface LST varies seasonally and is mainly controlled by the east- Asian monsoon. Subsurface LST is mainly affected by the intrusion of the North Pacific Tropical Water and the Kuroshio intrusion with net inflow into the South China Sea. Intermediate LST shows the persistent outflow resulted from the downwelling of the surface and upwelling of the deep layer to balance the inflow of the surface and deep layer. Deep LST is primarily influenced by the invasion of North Pacific Deep Water, which is mainly caused by the pressure gradient between the South China Sea with the stronger mixing and the Pacific with lower mixing.

2. ENSO Effects on the LST--> Monsoon Anomalies (Ma et al., 2010)(Wang et al., 1999) The key system that bridges the SCS climate and Pacific ENSO is an anomalous anti-cyclonic/cyclonic circulation located in the western North Pacific.

2. ENSO Effects on the LST--> Monsoon Anomalies The positive OLR and SLP anomalies around the areas between the equator and 10 o N indicate enhanced sinking motion and weakened convection in these areas. This enhanced subsidence reduces cloud cover and increases the amount of solar radiation absorbed by the ocean, which leads to enhanced SSTs over the western SCS. Local winds tend to be weaker during El Nino year and stronger during La Nina year. (Qiu et al., 2016)

Three types of Kuroshio intrusion through the Luzon Strait The nonlinear hysteresis of Kuroshio (Nan et al., 2015) (Qu et al., 2004) 2. ENSO Effects on the LST--> Kuroshio

(Tozuka et al., 2001) (Qiu et al., 2010) During El Nino years, the northward shift of the NEC bifurcation corresponds to a stronger Mindanao Dome and a weaker Kuroshio transport (Tozuka et al., 2002)

2. ENSO Effects on the LST--> Kuroshio As for the interannual variation, the correlation between the LST and the Kuroshio transport east of Luzon reaches 0.56, with the maximum (westward) LST leading the minimum (northward) Kuroshio transport by about 4 months. (A possible nonlinear hysteresis of the Kuroshio as a driving mechanism of LST). During El Nino years, the northward shift of the NEC bifurcation corresponds to a stronger Mindanao Dome and a weaker Kuroshio transport, thus providing a favorable condition for Pacific waters to penetrate into the SCS through Luzon Strait. (Qu et al., 2004)

The correlation between the LST and the South Oscillation index (SOI) reaches 0.63, with LST leading SOI by about 1 month. In general, the LST is stronger during El Nino years and weaker during La Nina. (Qu et al., 2004) 2. ENSO Effects on the LST

3. Conclusions ENSO the bifurcation of NEC northward Weaker east-Asian monsoon in Winter Weaker surface transport of Luzon Strait But the annual mean transport is westward Weaker Kuroshio Stronger LST Stronger intrusion of the North Pacific Tropical Water

4. Problems Is the deep layer transport of the Luzon Strait connected with ENSO? If so, through what ways does ENSO modulate the deep transport of the Luzon Strait?

Thanks !