The IOD signal in the upper-ocean Indonesian Throughflow since the mid-1970s

On the basis of simple ocean data assimilation (SODA) reanalysis product, the interannual variability of upper-ocean Indonesian Throughflow (ITF) volume transport since the mid 1970s is examed. The wavelet analysis shows a second prominent interannual oscillation with a period of about 2~4 a. To reveal any relationship between this band-scale oscillation of upper-ocean ITF and the Indian Ocean dipole (IOD), the correlation and wavelet analyses are used. The correlation coefficient between the upper-ocean ITF and the IOD reaches -0.40 with upper-ocean ITF lagging an IOD index by eight months. The wavelet power spectrum of upper-ocean ITF shows similar structure to that of the IOD index. And the evolution of IOD is reproduced by lagged correlation between the upper-ocean ITF and the sea surface temperature anomaly (SSTA) over the Indian Ocean. It suggests that the 2~4 a band-scale oscillation of upper-ocean ITF is related uniquely to the IOD over the tropical Indian Ocean.     

洋际通道的体积和热输运的年平均结构及季节变化：MOM4P1积分1400年的结果

The annual mean volume and heat transport sketches through the inter-basin passages and transoceanic sections have been constructed based on 1 400-year spin up results of the MOM4p1. The spin up starts from a state of rest, driven by the monthly climatological mean force from the NOAA World Ocean Atlas(1994). The volume transport sketch reveals the northward transport throughout the Pacific and southward transport at all latitudes in the Atlantic. The annual mean strength of the Pacific-Arctic-Atlantic through flow is 0.63×106 m3/s in the Bering Strait. The majority of the northward volume transport in the southern Pacific turns into the Indonesian through flow(ITF) and joins the Indian Ocean equatorial current, which subsequently flows out southward from the Mozambique Channel, with its majority superimposed on the Antarctic Circumpolar Current(ACC). This anti-cyclonic circulation around Australia has a strength of 11×106 m3/s according to the model-produced result. The atmospheric fresh water transport, known as P-E+R(precipitation minus evaporation plus runoff), constructs a complement to the horizontal volume transport of the ocean. The annual mean heat transport sketch exhibits a northward heat transport in the Atlantic and poleward heat transport in the global ocean. The surface heat flux acts as a complement to the horizontal heat transport of the ocean. The climatological volume transports describe the most important features through the inter-basin passages and in the associated basins, including: the positive P-E+R in the Arctic substantially strengthening the East Greenland Current in summer; semiannual variability of the volume transport in the Drake Passage and the southern Atlantic-Indian Ocean passage; and annual transport variability of the ITF intensifying in the boreal summer. The climatological heat transports show heat storage in July and heat deficit in January in the Arctic; heat storage in January and heat deficit in July in the Antarctic circumpolar current regime(ACCR); and intensified heat transport of the ITF in July. The volume transport of the ITF is synchronous with the volume transport through the southern Indo-Pacific sections, but the year-long southward heat transport of the ITF is out of phase with the heat transport through the equatorial Pacific, which is northward before May and southward after May. This clarifies the majority of the ITF originating from the southern Pacific Ocean.     

南海上层经向翻转环流的低频变化

The low-frequency variability of the shallow meridional overturning circulation(MOC) in the South China Sea(SCS) is investigated using a Simple Ocean Data Assimilation(SODA) product for the period of 1900–2010. A dynamical decomposition method is used in which the MOC is decomposed into the Ekman, external mode, and vertical shear components. Results show that all the three dynamical components contribute to the formation of the seasonal and annual mean shallow MOC in the SCS. The shallow MOC in the SCS consists of two cells: a clockwise cell in the south and an anticlockwise cell in the north; the former is controlled by the Ekman flow and the latter is dominated by the external barotropic flow, with the contribution of the vertical shear being to reduce the magnitude of both cells. In addition, the strength of the MOC in the south is found to have a falling trend over the past century, due mainly to a weakening of the Luzon Strait transport(LST) that reduces the transport of the external component. Further analysis suggests that the weakening of the LST is closely related to a weakening of the westerly wind anomalies over the equatorial Pacific, which leads to a southward shift of the North Equatorial Current(NEC) bifurcation and thus a stronger transport of the Kuroshio east of Luzon.     

Low-frequency variability of the North Equatorial Current bifurcation in the past 40 years from SODA

The low-frequency variability of the North Equatorial Current (NEC) bifurcation during 1958 to 2001 was investigated with the Simple Ocean Data Assimilation (SODA) 2.0.2 dataset.In agreement with recent observations,the NEC bifurcation latitude (NBL) shifted northward as depth increases, from about 12.7°N near the surface to about 17.1°N at depths around 500 m for the annual average. This study reveals that the interannual variations of NBL,with five years period,mainly focused on the upper 500 m with amplitude increasing as depth increased.The NBL shifted southward in the past 40 years,which was more significant in the subsurface at more than -0.02°/a.The NBL manifests itself in the transports of NMK (NEC-Mindanao Current (MC)-Kuroshio) system in strong relationship with MC (0.7) and Kuroshio (-0.7).The EOF analysis of meridional velocity off the Philippine coast shows that the first mode,explaining 62% of variance and 5 years period,was highly correlated with the southward shift of NBL with coefficient at about 0.75.The southward shift of NBL consists with the weakening of MC and strengthening of Kuroshio,which exhibited linear trends at -0.24Sv/a and 0.11Sv/a.Both interannual variation and trend of NBL were closely related to the variation of NMK system.     

热带太平洋波浪输运与海表面温度异常关系研究

Large-scale water transport is one of the key factors that affect sea surface temperature anomaly(SSTA) in the eastern equatorial Pacific(EEP).The relationship between the wave transport in the tropical Pacific and the SSTA in the EEP is examined by different methods,including band-pass filtering,period analysis,correlation analysis,significant analysis,and empirical orthogonal function(EOF) analysis.We have found that the eastward shift of the wave transport anomaly in the tropical Pacific,with a period of 2 a and enhancing the transport of warm waters from the western Pacific warm pool,precedes the increase of sea surface temperature(SST) in the EEP.The wave transport and the SSTA in the EEP have a maximum correlation of 0.65 with a time-lag of 6 months(transport variation precedes the temperature).The major periods(3.7 a and 2.45 a) of the wave transport variability,as revealed by the EOF analysis,appear to be consistent with the SSTA oscillation cycle in the EEP.Based on the first occurrence of a significant SSTA in the Ni?o 3 region(5°S–5°N,90°–150°W),two types of warm events are defined.The wave transport anomalies in two types present predominantly the west anomaly in the tropical Pacific,it is that the wave transport continues transport warm water from west to east before the onset of the warm event.The impact of wave-induced water transport on the SSTA in the EEP is confirmed by the heat flux of the wave transport.The wave transport exerts significant effect on the SSTA variability in the EEP and thus is not neglectable in the further studies.     

Multitime scale variations of sea surface temperature in the China seas based on the HadISST dataset

The variability of the sea surface temperature(SST) in the China seas has been studied in seasonal,interannual and interdecadal scales based on the monthly data of HadISST spanning from 1870 to 2007. The main results obtained are SST in the China offshore changes most actively at the seasonal scale with the intensity diminishing from north to south,as the temperature differences between summer and winter reaching 17 and 4 C in the northern and southern areas,respectively. Moreover,seasonal variation near the coastal regions seems relatively stronger than that far from the coastline;significant interannual variations are detected,with the largest positive anomaly occurring in 1998 in the overall area. But as far as different domains are concerned,there exists great diversity,and the difference is also found between winter and summer. Differed from the seasonal variations,where the strongest interannual variability takes place,resides to the south of that of the seasonal ones in the northern section,nevertheless in the South China Sea,the most significant interannual variability is found in the deep basin;interdecadal changes of summer,winter and annual mean SST in different domains likewise present various features. In addition,a common dominant warming in recent 20 a are found in the overall China offshore with the strongest center located in the vicinity of the Changjiang Estuary in the East China Sea,which intensifies as high as 1.3 C during the past 130 a.     

Interannual variability in the Mindanao Eddy and its impact on thermohaline structure pattern

The major feature,interannual variability and variation cause of the Mindanao Eddy and its impact on the thermohaline structure are analyzed based on the Argo profiling float data,the history observed data and the SODA data.The analysis results show that the Mindanao Eddy is a permanent cyclonic meso-scale eddy and spreads vertically from about 500 m depth upward do about 50 m depth.In addition to its strong seasonal variability,the Mindanao Eddy displays a remarkable interannual variability associated with ENSO.It strengthens and expands eastward during El Nin o while it weakens and retreats westward during La Nin a.The interannual variability in the Mindanao Eddy may be caused by the North Equatorial Counter Current,the North Equatorial Current,the Mindanao Current and the Indonesian Through Flow.The eddy variability can have a great influence on the thermohaline structure pattern in the local upper ocean.When the eddy is strong,the cold and low salinity water inside the eddy moves violently upward from deep layer,the thermocline depth greatly shoals,and the subsurface high salinity water largely decreases,with the upper mixed layer becoming thinner,and vice versa.     

Response of winter cohort abundance of Japanese common squid Todarodes pacificus to the ENSO events

The Japanese common squid Todarodes pacificus is an economically important species with one year lifespan,which is significantly influenced by climatic and environmental variability. According to the fishery data of the winter cohort of T. pacificus from 2003 to 2012, as well as environmental data and the Oceanic Ni?o index(ONI,which was defined by the sea surface temperature(SST) anomaly in the Ni?o 3.4 region), variations in the SST,chlorophyll a(Chl a) concentration, suitable spawning area(SSA) and sea surface height anomaly(SSHA) on the spawning ground of T. pacificus were examined under the El Ni?o and La Ni?a conditions. Their influences on squid abundance(defined by catch per unit effort, CPUE) were further assessed. The results showed that seasonal changes were found in SST, Chl a and SSA on the spawning ground of T. pacificus. Correlation analysis suggested that annual CPUE was significantly positively correlated with Chl a and SSA(p0.05), but had insignificant relationship with SST(p0.05). Moreover, the El Ni?o and La Ni?a events tended to dominate the changes of SSA and Chl a concentration in the key area between 25°–29°N and 122.5°–130.5°E, driving the variability of squid abundance. However, this influence varied with the intensity of each anomalous climatic event: the weak El Ni?o event occurred, the spawning ground was occupied by waters with enlarged SSA but with extremely low Chl a concentration, leading to low squid recruitment, the CPUE then decreased; the moderate intensity of El Ni?o event resulted in shrunk SSA but with high Chl a concentration on the spawning ground, the squid recruitment and CPUE increased; the moderate intensity of La Ni?a events yielded elevated SSA and high Chl a concentration on the spawning ground, the squid recruitment and CPUE dramatically increased. Our findings suggested that the ENSO events played crucial effects on the incubating and feeding conditions of the winter cohort of T. pacificus during the spawning season and ultimately affected its abundance.     

Climatology and seasonal variability of theMindanao Undercurrent based on OFES data

The simulation of an ocean general circulation model for the earth simulator （OFES） is transformed to an isopycnal coordinate to investigate the spatial structure and seasonal variability of the Mindanao Under- current （MUC）. The results show that （1） potential density surfaces, δ0=26.5 and δ0=27.5, can be chosen to encompass the M UC layer. Southern Pacilic tropical water （SPTW）, Antarctic Intermediate Water （AAIW） and high potential density water （HPDW） constitute the MUC. （2） Climatologically, the MOC exists in the form of dual-core. In some months, the dual-core structure changes to a single-core structure. （3） Choosing section at 8°N for calculating the transport of the MUC transport is reliable. Potential density constraint provides a good method for calculating the transport of the MOC. （4） The annual mean transport of the MUC is 8.34 × 106 m3/s and varies considerably with seasons： stronger in late spring and weaker in winter.     

近岸波浪和波生流环境中泥沙输运的数值模拟

Owing to lack of observational data and accurate definition,it is difficult to distinguish the Kuroshio intrusion water from the Pacific Ocean into the South China Sea(SCS).By using a passive tracer to identify the Kuroshio water based on an observation-validated three-dimensional numerical model MITgcm,the spatio-temporal variation of the Kuroshio intrusion water into the SCS has been investigated.Our result shows the Kuroshio intrusion is of distinct seasonal variation in both horizontal and vertical directions.In winter,the intruding Kuroshio water reaches the farthest,almost occupying the area from 18°N to 23°N and 114°E to 121°E,with a small branch flowing towards the Taiwan Strait.The intrusion region of the Kuroshio water decreases with depth gradually.However,in summer,the Kuroshio water is confined to the east of 118°E without any branch reaching the Taiwan Strait;meanwhile the intrusion region of the Kuroshio water increases from the surface to the depth about 205 m,then it decreases with depth.The estimated annual mean of Kuroshio Intrusion Transport(KIT) via the Luzon Strait is westward to the SCS in an amount of –3.86×106 m3/s,which is larger than the annual mean of Luzon Strait Transport(LST) of –3.15×106 m3/s.The KIT above 250 m accounts for 60%–80% of the LST throughout the entire water column.By analyzing interannual variation of the Kuroshio intrusion from the year 2003 to 2012,we find that the Kuroshio branch flowing into the Taiwan Strait is the weaker in winter of La Ni?a years than those in El Ni?o and normal years,which may be attributed to the wind stress curl off the southeast China then.Furthermore,the KIT correlates the Ni?o 3.4 index from 2003 to 2012 with a correlation coefficient of 0.41,which is lower than that of the LST with the Ni?o 3.4 index,i.e.,0.78.     

2015/2016年超强厄尔尼诺期间热带西太平洋海洋环流变化特征

本文利用HYCOM （Hybrid Coordinate Ocean Model）再分析数据对北赤道流（NEC）、棉兰老流（MC）以及黑潮（KC）所构成的NMK环流系统在2015/2016年超强厄尔尼诺事件期间的变化特征及其影响机制进行了研究，并与其他厄尔尼诺期间的变化特征进行了对比。结果表明，在2015/2016年超强厄尔尼诺事件期间，NEC和MC输运均显著增强，最大值分别达到66 Sv （1 Sv=10⁶ m³/s）和49.4 Sv，北赤道流分叉纬度最北可达16°N，KC输运没有明显增强。NMK环流系统的年际变化主要与此次厄尔尼诺事件期间热带西北太平洋15°N以南、160°E以西海域出现的气旋式环流异常有关。该环流异常出现自厄尔尼诺事件的前期阶段，并于爆发阶段达到顶峰，主要是由15°N以南区域出现的强西风异常所引起的。进一步分析表明，此次厄尔尼诺事件期间NEC、MC输运和NBL的平均值均大于1992— 2014年间所有厄尔尼诺事件的平均状况，但与1997/1998年超强厄尔尼诺事件期间的平均值相近。     

ENSO循环相联系的北太平洋低纬度异常西边界流

用SODA海洋同化和NCEP大气再分析资料,分析了热带太平洋次表层海温异常主要模态与北太平洋低纬度西边界流海域上层海洋环流和亚洲-北太平洋地区大气垂直和水平流场变化之间的关系,得到以下结果:（1） 在热带太平洋海洋次表层ENSO事件具有两种模态,二者组合构成ENSO循环。第一模态为ENSO成熟期,主要出现在冬季,第二模态为ENSO过渡期,主要出现夏季。（2） ENSO循环对北太平洋低纬度西边界流区上层海洋环流有重要影响。在El Niño发展期或La Niña 衰退期,该区出现气旋性异常环流,北赤道流（NEC）加强,NEC分叉位置北移,棉兰老海流（MC）加大,菲律宾以东黑潮（KC）减小,北赤道逆流（NECC）最强。在El Niño（La Niña）成熟期,该区气旋性（反气旋性）异常环流达最强,NEC最强（最弱）,NEC分叉位置最北（最南）,MC最大（最小）,KC最小（最大）,NECC减弱（加强）。在El Niño衰退期或La Niña发展期与El Niño发展期相反,该区出现反气旋性异常环流,由此导致相应流系异常发生反位相变化。（3） ENSO循环对北太平洋低纬度西边界流海域上层海洋环流的影响是通过ENSO事件期间热带太平洋热力状况异常改变上空大气环流来实现的。ENSO事件首先造成热带太平洋海洋热力状况异常,导致其上空对流活动异常,后者直接或间接通过“大气桥”能量传输引起相关地区大气环流场的变化,致使海面风应力场异常,进而强迫上层海洋环流场的相应变化。文章最后还分析了ENSO事件期间菲律宾附近异常反气旋或异常气旋性风场的产生和持续原因,讨论了北太平洋低纬度西边界流海域海气相互作用在ENSO循环中的贡献。     

区域海气耦合模式FROALS模拟的西北太平洋环流及其年际变率

本文利用区域海气耦合模式FROALS(Flexible Regional Ocean-Atmosphere-Land System)对西北太平洋地区1984-2007年连续积分结果,对比SODA(Simple Ocean Data Assimilation)同化资料讨论了西北太平洋海表温度和表层洋流的气候态及年际变率。结果表明,FROALS基本能够再现冬、夏季季节平均的海温型,但均存在一个明显的冷偏差;FROALS对气候平均态的表层洋流有较高的模拟技巧,对于冬、夏季的表层洋流型都能够再现。另外,表层洋流的模拟偏差与海表高度的模拟偏差直接相关。由于模式模拟的黑潮热输送较观测偏强,使得模式模拟的海洋热输送倾向于使黑潮路径上的海温呈现正偏差。从表层洋流的年际变率来看,模式模拟的与ENSO(El Nio-South Oscillation)相联系的年际变率信号与观测相似:在El Nio年,北赤道流和棉兰老流增强,低纬度西太平洋海表高度降低,而在La Nia年则呈现出相反的形态,但是在模式中这种信号稍强于观测。     

中国科学院气候系统模式模拟的ENSO循环

On the basis of more than 200-year control run, the performance of the climate system model of Chinese Academy of Sciences(CAS-ESM-C) in simulating the El Ni?o-Southern Oscillation(ENSO) cycle is evaluated, including the onset, development and decay of the ENSO. It is shown that, the model can reasonably simulate the annual cycle and interannual variability of sea surface temperature(SST) in the tropical Pacific, as well as the seasonal phase-locking of the ENSO. The model also captures two prerequisites for the El Ni?o onset, i.e., a westerly anomaly and a warm SST anomaly in the equatorial western Pacific. Owing to too strong forcing from an extratropical meridional wind, however, the westerly anomaly in this region is largely overestimated. Moreover, the simulated thermocline is much shallower with a weaker slope. As a result, the warm SST anomaly from the western Pacific propagates eastward more quickly, leading to a faster development of an El Ni?o. During the decay stage, owing to a stronger El Ni?o in the model, the secondary Gill-type response of the tropical atmosphere to the eastern Pacific warming is much stronger, thereby resulting in a persistent easterly anomaly in the western Pacific. Meanwhile, a cold anomaly in the warm pool appears as a result of a lifted thermocline via Ekman pumping. Finally, an El Ni?o decays into a La Ni?a through their interactions. In addition, the shorter period and larger amplitude of the ENSO in the model can be attributed to a shallower thermocline in the equatorial Pacific, which speeds up the zonal redistribution of a heat content in the upper ocean.     

ITF in a coupled GCM and its interannual variability related to ENSO and IOD

1 Introduction Indonesian Throughflow (ITF) connects the Indian and Pacific Oceans at low latitudes. There is the well- known interannual variability, El Ni%o, over the tropical Pacific. The recent finding of Indian Ocean Dipole (IOD) (Saji et al., 1999; …     

冬季吕宋岛西温度锋的年际变化

Interannual variability of thermal front west of Luzon Island during the winter of 1993–2013 is examined with the method of singular value decomposition(SVD) and a suite of satellite measurements in this paper. It is found that both the area and intensity of the thermal front west of Luzon Island show apparent interannual variability.Further study based on SVD shows that the interannual variability of the thermal front is highly associated with El Ni?o and Southern Oscillation(ENSO), and the correlation coefficient between Ni?o3.4 index and the first Principal Component(PC1) of thermal front can reach –0.65. The mechanism can be described as follows. In El Ni?o(La Ni?a) years, the East Asian winter monsoon(EAWM) is weakened(enhanced), inducing weaker(stronger) local wind stress curl(WSC) west of Luzon Island, and resulting in weakened(enhanced) Luzon cold eddy, which finally leads to the weakening(enhancement) of the thermal front.     

热带太平洋海平面低频变化

本文选取ECMWF ORAS4再分析数据对1959-2015年热带太平洋海平面的低频变化进行了分析。热带太平洋海平面年际变化第一模态反映了ENSO爆发阶段的海平面变化,热带东、西太平洋变化反相,其时间序列与Niño3.4指数高度相关。海平面第二模态则体现了El Niño爆发前后热带太平洋暖水的输运过程。El Niño爆发前热带西太平洋暖水聚集的位置,以及爆发后暖水向赤道外输运的位置在两类El Niño事件中均有所不同。此外,ENSO的周期在近半个世纪发生了显著的年代际变化,这一变化与热带太平洋的年代际变化有关。热带太平洋的年代际变化对海平面趋势变化也有着显著的影响。卫星高度计观测到的近20年海平面的快速上升（下降）正是由20世纪90年代后热带太平洋频繁的位相转换引起的。     

印度尼西亚贯穿流的年际变化:一个全球变网格海洋模式的初步模拟结果

使用1994～2000年NCEP风应力资料驱动全球变网格环流模式，得出印度尼西亚贯穿流(ITF)流量的年际变化时间序列。模拟结果显示：ITF流量的年际变化与太平洋和印度洋的年际变化均有密切联系，在El Ni~↑no年流量偏低，在La Ni~↑no年流量偏高；ITF流量的年际变化与Ni~↑no 3区指数呈显著负相关，Ni~↑no 3区指数超前ITF流量2个月时负相关系数达到最大，为-0．81；与南方涛动指数(SOI)明显呈正相关，SOI超前ITF流量2个月时相关系数达到最大，为0．72；与印度洋偶极子(IOD)指数负相关，IOD指数超前ITF流量3个月时负相关系数达到最大，为-0．74。     

冬季婆罗洲岛西北沿岸上升流的时空特征及机理研究

Winter coastal upwelling off northwest Borneo in the South China Sea(SCS) is investigated by using satellite data, climatological temperature and salinity fields and reanalysis data. The upwelling forms in December, matures in January, starts to decay in February and almost disappears in March. Both Ekman transport induced by the alongshore winter monsoon and Ekman pumping due to orographic wind stress curl are favorable for the upwelling. Transport estimates demonstrate that the month-to-month variability of Ekman transport and Ekman pumping are both consistent with that of winter coastal upwelling, but Ekman transport is two times larger than Ekman pumping in January and February. Under the influence of El Ni?o-Southern Oscillation(ENSO), the upwelling shows remarkable interannual variability: during winter of El Ni?o(La Ni?a) years, an anticyclonic(a cyclonic) wind anomaly is established in the SCS, which behaves a northeasterly(southwesterly) anomaly and a positive(negative) wind stress curl anomaly off the northwest Borneo coast, enhancing(reducing) the upwelling and causing anomalous surface cooling(warming) and higher(lower) chlorophyll concentration. The sea surface temperature anomaly(SSTA) associated with ENSO off the northwest Borneo coast has an opposite phase to that off southeast Vietnam, resulting in a SSTA seesaw pattern in the southern SCS in winter.     

Variations of eddy kinetic energy in the South China Sea

Fifteen years of merged altimetric data were used to acquire the seasonal to interanual variations of eddy kinetic energy (EKE) in the South China Sea (SCS). The results show that climatological mean EKE in the SCS ranges from 50 cm²/s² to 1,400 cm²/s², with high values in the regions southeast of Vietnam and southwest of Taiwan Island. The amplitude of the annual harmonic of the EKE is characterized by high values to the southeast of Vietnam where the maximum exceeds 800 cm²/s². The EKE in the northern SCS reaches its maximum in August-February, while it peaks in September–December in the southern SCS. Besides the seasonal variation, the EKE also shows strong interannual variation, which has a negative (positive) anomaly in boreal winter during El Niño (La Niña) events. The interannual variation of local wind stress curl associated with El Niño-Southern Oscillation events may be the cause of the interannual variation of the EKE in the SCS.