Eddies are frequently observed in the northeastern South China Sea(SCS).However,there have been few studies on vertical structure and temporal-spatial evolution of these eddies.We analyzed the seasonal Luzon Warm Eddy(LWE) based on Argo float data and the merged data products of satellite altimeters of Topex/Poseidon,Jason-1 and European Research Satellites.The analysis shows that the LWE extends vertically to more than 500 m water depth,with a higher temperature anomaly of 5°C and lower salinity anomaly of 0.5 near the thermocline.The current speeds of the LWE are stronger in its uppermost 200 m,with a maximum speed of 0.6 m/s.Sometimes the LWE incorporates mixed waters from the Kuroshio Current and the SCS,and thus has higher thermohaline characteristics than local marine waters.Time series of eddy kinematic parameters show that the radii and shape of the LWE vary during propagation,and its eddy kinetic energy follows a normal distribution.In addition,we used the empirical orthogonal function(EOF) here to analyze seasonal characteristics of the LWE.The results suggest that the LWE generally forms in July,intensifies in August and September,separates from the coast of Luzon in October and propagates westward,and weakens in December and disappears in February.The LWE's westward migration is approximately along 19°N latitude from northwest of Luzon to southeast of Hainan,with a mean speed of 6.6 cm/s.
We used fifteen years (1993-2007) of altimetric data,combined from different missions (ERS-1/2,TOPEX/Poseidon,Jason-1,and Envisat),to analyze the variability of the eddy kinetic energy (EKE) in the South China Sea (SCS).We found that the EKE ranged from 64 cm2/s2 to 1 390 cm2/s2 with a mean value of 314 cm2/s2.The highest EKE center was observed to the east of Vietnam (with a mean value of 509 cm2/s2) and the second highest EKE region was located to the southwest of Taiwan Island (with a mean value of 319 cm2/s2).We also found that the EKE structure is the consequence of the superposition of different variability components.First,interannual variability is important in the SCS.Spectral analysis of the EKE interannual signal (IA-EKE) shows that the main periodicities of the IA-EKE to the east of Vietnam,to the southwest of Taiwan Island,and in the SCS are 3.75,1.87,and 3.75 years,respectively.It is to the south of Taiwan Island that the IA-EKE signal has the most obvious impact on EKE variability.In addition,the IA-EKE exhibit different trends in different regions.An obvious positive trend is observed along the east coast of Vietnam,while a negative trend is found to the southwest of Taiwan Island and in the east basin of Vietnam.Correlation analysis shows that the IA-EKE has an obvious negative correlation with the SSTA in Nio3 (5°S-5°N,90°W-150°W).El Nio-Southern Oscillation (ENSO) affects the IA-EKE variability in the SCS through an atmospheric bridge-wind stress curl over the SCS.Second,the seasonal cycle is the most obvious timescale affecting EKE variability.The locations of the most remarkable EKE seasonal variabilities in the SCS are to the east of Vietnam,to the southwest of Taiwan,and to the west of Philippines.To the east of Vietnam,the seasonal cycle is the dominant mechanism controlling EKE variability,which is attributed primarily to the annual cycle there of wind stress curl.In this area,the maximum EKE is observed in autumn.To the southwest of Taiwan Island,the EKE is enlarged by the stro
Using interpolation and averaging methods, we analyzed the sea surface wind data obtained from December 1992 to November 2008 by the scatterometers ERS-1, ERS-2, and QuikSCAT in the area of 2°N–39 °N, 105°E–130°E, and we reported the monthly mean distributions of the sea surface wind field. A vector empirical orthogonal function (VEOF) method was employed to study the data and three temporal and spatial patterns were obtained. The first interannual VEOF accounts for 26% of the interannual variance and displays the interannual variability of the East Asian monsoon. The second interannual VEOF accounts for 21% of the variance and reflects the response of China sea winds to El Nio events. The temporal mode of VEOF-2 is in good agreement with the curve of the Nio 3.4 index with a four-month lag. The spatial mode of VEOF-2 indicates that four months after an El Nio event, the southwesterly anomalous winds over the northern South China Sea, the East China Sea, the Yellow Sea, and the Bohai Sea can weaken the prevailing winds in winter, and can strengthen the prevailing winds in summer. The third interannual VEOF accounts for 10% of the variance and also reflects the influence of the ENSO events to China Sea winds. The temporal mode of VEOF-3 is similar to the curve of the Southern Oscillation Index. The spatial mode of VEOF-3 shows that the northeasterly anomalous winds over the South China Sea and the southern part of the East China Sea can weaken the prevailing winds, and southwesterly anomalous winds over the northern part of the East China Sea, the Yellow Sea, and the Bohai Sea can strengthen the prevailing winds when El Nio occurs in winter. If El Nio happens in summer, the reverse is true.
Using a 1.5-layer reduced-gravity nonlinear shallow-water equation model, we studied the effect of the meridional wind on the western boundary currents (WBC) at critical states with hysteresis courses. The results of the simulation indicate that the WBC is prone to penetrating into the gap under northerly winds, and its path is more difficult to alter due to the larger interval between the two critical transition curves (C1P and C1L). For southerly winds, the WBC is prone to leaping across the gap, and its path is easier to alter due to the smaller interval between the two critical transition curves. The simulation results also indicate that the meridional winds over the southern region of the gap are the dominant factor determining the formation of the WBC. The dynamic mechanism influencing the transport of WBC near the gap is both Ekman transport and the blocking of Ekman transport. Ekman transport induced by northerly winds may reduce the transport of the WBC, causing the β-effect to dominate the meridional advection (promoting the penetration). Southerly winds, however, may enhance the transport of the WBC, causing the meridional advection to dominate the β-effect (promoting the leaping state). These results explain some structural features of the Kuroshio at the Luzon Strait.
Using a 1.5 layer nonlinear shallow-water reduced-gravity model, we executed numerical simulations to investigate the possibility of a western boundary current (WBC) path transition due to mesoscale eddies based on the background of the Kuroshio intrusion into the South China Sea (SCS) from the Luzon Strait. Because the WBC existed different current states with respect to different wind stress control parameters, we chose three steady WBC states (loop current, eddy shedding and leaping) as the background flow field and simulated the path transition of the WBC due to mesoscale eddies. Our simulations indicated that either an anticyclonic or cyclonic eddy can lead to path transition of the WBC with different modes. The simulation results also show that the mesoscale eddies can lead to path transition of the WBC from loop and eddy shedding state to leaping state because of the hysteresis effect. The leaping state is relatively stable compared with the mesoscale eddies. Moreover, an anticyclonic eddy is more effective in producing the WBC path transition for the path transition than a cyclonic eddy. Our results may help to explain some phenomena observed regarding the path transition of the Kuroshio due to the mesoscale eddies at the Luzon Strait.
The thermal condition anomaly of the western Pacific warm pool and its zonal displacement have very important influences on climate change in East Asia and even the whole world. However, the impact of the zonal wind anomaly over the Pacific Ocean on zonal displacement of the warm pool has not yet been analyzed based on long-term record. Therefore, it is important to study the zonal displacement of the warm pool and its response to the zonal wind anomaly over the equatorial Pacific Ocean. Based on the NCDC monthly averaged SST (sea surface temperature) data in 2°×2° grid in the Pacific Ocean from 1950 to 2000, and the NCEP/NCAR global monthly averaged 850 hPa zonal wind data from 1949 to 2000, the relationships between zonal displacements of the western Pacific warm pool and zonal wind anomalies over the tropical Pacific Ocean are analyzed in this paper. The results show that the zonal displacements are closely related to the zonal wind anomalies over the western, central and eastern equatorial Pacific Ocean. Composite analysis indicates that during ENSO events, the warm pool displacement was trigged by the zonal wind anomalies over the western equatorial Pacific Ocean in early stage and the process proceeded under the zonal wind anomalies over the central and eastern equatorial Pacific Ocean unless the wind direction changes. Therefore, in addition to the zonal wind anomaly over the western Pacific, the zonal wind anomalies over the central and eastern Pacific Ocean should be considered also in investigation the dynamical mechanisms of the zonal displacement of the warm pool.
基于热带太平洋SST和850 hPa风资料,分析了西太平洋暖池东界和东太平洋暖池南界的年际和年代际变异,并探讨了赤道太平洋纬向风异常对西太平洋暖池纬向运移的驱动作用以及热带东北太平洋经向风异常对东太平洋暖池经向变动的影响。在此基础上,研究了西太平洋暖池和东太平洋暖池变异对ENSO循环的联合影响,并提出了一个联合影响指数。结果表明,当联合指数为1.6时,有可能出现一次新的El Ni o事件。这为ENSO的形成和演变机制研究提供了一个新的线索。
Seasonal variations of water exchange in the Luzon Strait are studied numerically using the improved Princeton Ocean Model （POM） with a consideration of the effects of connectivity of South China Sea （SCS） and monsoons. The numerical simulations are carried out with the strategy of variable grids, coarse grids for the Pacific basin and fine grids for the SCS. It is shown that the Mindoro Strait plays an important role in adjusting the water balance between the Pacific and the SCS. The SCS monsoon in summer seasons hinders the entrance of the Pacific water into the SCS through the Luzon Strait while the SCS monsoon in winter seasons promotes the entrance of Pacific water into the SCS through the Luzon Strait. However, the SCS monsoon does not affect the annual mean Luzon Strait transport, as is mainly determined by the Pacific basin wind.
