Seasonal variability of the North Equatorial Current transport in the western Pacific Ocean

Seasonal variability of the North Equatorial Current （NEC） transport in the western Pacific Ocean is investigated with ECMWF Ocean Analysis/Reanalysis System 3 （eRA-S3）. The result shows that NEC transport （NT） across different longitudes in the research area shows a similar double-peak structure, with two maxima （in summer and winter）, and two minima （in spring and autumn）. This kind of structure can also be found in NEC geostrophic transport （NGT）, but in a different magnitude and phase. These differences are attributable to Ekman transport induced by the local meridional wind and transport caused by nonzero velocity at the reference level, which is assumed to be zero in the NGT calculation. In the present work, a linear vorticity equation governing a 1.5-layer reduced gravity model is adopted to examine the dynamics of the seasonal variability of NGT. It is found that the annual cycle of NGT is mainly controlled by Ekman pumping induced by local wind, and westward-propagating Rossby waves induced by remote wind. Further research demonstrates that the maximum in winter and minimum in spring are mostly attributed to wind east of the dateline, whilst the maximum in summer and minimum in autumn are largely attributed to that west of the dateline.     

Eddy induced SST variation and heat transport in the western North Pacific Ocean

Journal of Oceanology and Limnology - Vigorous mesoscale eddies and significant sea surface temperature (SST) variations are found in the northern edge of the Pacific warm pool that features large...     

Seasonal variation of the surface North Equatorial Countercurrent (NECC) in the western Pacific Ocean

The North Equatorial Countercurrent(NECC) is an important zonal fl ow in the upper circulation of the tropical Pacifi c Ocean, which plays a vital role in the heat budget of the western Pacifi c warm pool. Using satellite-derived data of ocean surface currents and sea surface heights(SSHs) from 1992 to 2011, the seasonal variation of the surface NECC in the western tropical Pacifi c Ocean was investigated. It was found that the intensity(INT) and axis position(Y_(CM)) of the surface NECC exhibit strikingly different seasonal fl uctuations in the upstream(128°–136°E) and downstream(145°–160°E) regions. Of the two regions, the seasonal cycle of the upstream NECC shows the greater interannual variability. Its INT and Y CM are greatly infl uenced by variations of the Mindanao Eddy, Mindanao Dome(MD), and equatorial Rossby waves to its south. Both INT and YC M also show semiannual signals induced by the combined effects of equatorial Rossby waves from the Central Pacifi c and local wind forcing in the western Pacifi c Ocean. In the downstream region, the variability of the NECC is affected by SSH anomalies in the MD and the central equatorial Pacifi c Ocean. Those in the MD region are especially important in modulating the Y CM of the downstream NECC. In addition to the SSH-related geostrophic fl ow, zonal Ekman fl ow driven by meridional wind stress also plays a role, having considerable impact on INT variability of the surface NECC. The contrasting features of the variability of the NECC in the upstream and downstream regions refl ect the high complexity of regional ocean dynamics.     

Heat and salt transport throughout the North Pacific Ocean

Absolute geostrophic currents in the North Pacific Ocean are calculated using the P-vector method and gridded Argo profiling data from January 2004 to December 2012. Three-dimensional structures and seasonal variability of meridional heat transport (MHT) and meridional salt transport (MST) are analyzed. The results show that geostrophic and Ekman components are generally opposite in sign, with the southward geostrophic component dominating in the subtropics and the northward Ekman component dominating in the tropics. In combination with the net surface heat flux and the MST through the Bering Strait, the MHT and MST of the western boundary currents (WBCs) are estimated for the first time. The results suggest that the WBCs are of great importance in maintaining the heat and salt balance of the North Pacific. The total interior MHT and MST in the tropics show nearly the same seasonal variability as that of the Ekman components, consistent with the variability of zonal wind stress. The geostrophic MHT in the tropics is mainly concentrated in the upper layers, while MST with large amplitude and annual variation can extend much deeper. This suggests that shallow processes dominate MHT in the North Pacific, while MST can be affected by deep ocean circulation. In the extratropical ocean, both MHT and MST are weak. However, there is relatively large and irregular seasonal variability of geostrophic MST, suggesting the importance of the geostrophic circulation in the MST of that area.     

Zonal displacement of western Pacific warm pool and zonal wind anomaly over the Pacific Ocean

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.     

Subsurface temperature anomalies in the North Pacific Ocean associated with the ENSO cycle

Journal of Oceanology and Limnology - Multi-year Simple Ocean Data Assimilation (SODA) and National Centers for Environmental Prediction (NCEP) datasets were used to investigate the leading...     

Interannual variability of transport and bifurcation of the North Equatorial Current in the tropical North Pacific Ocean

The relationship of the interannual variability of the transport and bifurcation latitude of the North Equatorial Current (NEC) to the El Ni o-Southern Oscillation (ENSO) is investigated. This is done through composite analysis of sea surface height (SSH) observed by satellite altimeter during October 1992-July 2009, and correspondingly derived sea surface geostrophic currents. During El Nio/La Ni a years, the SSH in the tropical North Pacific Ocean falls/rises, with maximum changes in the region 0-15°N, 130°E-160°E. The decrease/increase in SSH induces a cyclonic/anticyclonic anomaly in the western tropical gyre. The cyclonic/anticyclonic anomaly in the gyre results in an increase/decrease of NEC transport, and a northward/southward shift of the NEC bifurcation latitude near the Philippine coast. The variations are mainly in response to anomalous wind forcing in the west-central tropical North Pacific Ocean, related to ENSO events.     

Current structure and its variation in the equatorial area of the western north Pacific Ocean

Based on the current measurement data from the R/V Ryofu Maru of JMA in the equatorial area along 137°E (1972–83) and 155°E (1972–79) the structures of the zonal velocity of the Equatorial Undercurrent (EUC) and the North Equatorial Countercurrent (NECC) and their variations are systematically analyzed in detail. At 155°E, the current at the equator and 100–300 m depth was a typical eastward EUC, it intensified in 1973–75, i.e., in the non-El Niño period. While the corresponding current at 137°E was mostly westward, and the origin of the EUC shifted to north of the equator around 0.5–1.5°N owing to the influence of the New Guinea Coast. The EUC origin disappeared in early July, 1982. Comparing with the EUC disappearance at 159°W, the average speed of an eastward travelling wave would be～1.1m/s. The velocity core of the NECC at 137°E generally shifted northward in winter and southward in summer, and was stronger in summer and weaker in winter. The fluctuations of the NECC were closely related to those of the wind stress curl over the region 2–10°N, 160°E–150°W.     

Review on observational studies of western tropical Pacific Ocean circulation and climate

The Western Tropical Pacific(WTP) Ocean holds the largest area of warm water(28℃) in the world ocean referred to as the Western Pacific Warm Pool(WPWP),which modulates the regional and global climate through strong atmospheric convection and its variability.The WTP is unique in terms of its complex 3-D ocean circulation system and intensive multiscale variability,making it crucial in the water and energy cycle of the global ocean.Great advances have been made in understanding the complexity of the WTP ocean circulation and associated climate impact by the international scientific community since the 1960 s through field experiments.In this study,we review the evolving insight to the 3-D structure and multi-scale variability of the ocean circulation in the WTP and their climatic impacts based on in-situ ocean observations in the past decades,with emphasis on the achievements since 2000.The challenges and open que stions remaining are reviewed as well as future plan for international study of the WTP ocean circulation and climate.     

20世纪80年代初以来北太平洋海温变化特征

应用1979.1-2006.12北太平洋海表温度（SST）资料,采用一元线性回归、功率谱等统计方法对该区SST的变化特征进行分析,结果表明：（1）北太平洋SST年际变化较为显著,尤其在靠近亚洲大陆一带洋面、北太平洋中部中纬度海域及赤道中、东太平洋;（2）北太平洋西部和中部SST1-12月均呈上升趋势,靠近亚洲大陆的日本海一带和我国大陆以东洋面升温最快。除我国以东洋面升温中心在冬季外,其余海域升温均在夏秋季更迅速,20世纪90年代初以来尤为明显;北美海岸山脉以西及赤道中、东太平洋SST则呈弱的下降趋势;（3）赤道中、东太平洋春夏季存在显著5a和3.5a左右的年际变化;北太平洋中部30°N一带冬春季存在5-6a左右的年际变化和约14a的年代际变化;（4）除北太平洋中部（西风漂流区）外,各个海域大部分月份SST高值年和低值年分别与厄尔尼诺年和拉尼娜年对应,西风漂流区SST高值年均出现在20世纪末21世纪初,低值年与厄尔尼诺年对应。     

Variability of tropical cyclone in high frequent occurrence regions over the western North Pacific

In this study, three high frequent occurrence regions of tropical cyclones(TCs), i.e., the northern South China Sea(the region S), the south Philippine Sea(the region P) and the region east of Taiwan Island(the region E), are defined with frequency of TC's occurrence at each grid for a 45-year period(1965–2009), where the frequency of occurrence(FO) of TCs is triple the mean value of the whole western North Pacific. Over the region S, there are decreasing trends in the FO of TCs, the number of TCs' tracks going though this region and the number of TCs' genesis in this region. Over the region P, the FO and tracks demonstrate decadal variation with periods of 10–12 year, while over the region E, a significant 4–5 years' oscillation appears in both FO and tracks. It is demonstrated that the differences of TCs' variation in these three different regions are mainly caused by the variation of the Western Pacific Subtropical High(WPSH) at different time scales. The westward shift of WPSH is responsible for the northwesterly anomaly over the region S which inhibits westward TC movement into the region S. On the decadal timescale, the WPSH stretches northwestward because of the anomalous anticyclone over the northwestern part of the region P, and steers more TCs reaching the region P in the greater FO years of the region P. The retreating of the WPSH on the interannual time scale is the main reason for the FO's oscillation over the region E.     

The impact of meso-scale eddies on the Subtropical Mode Water in the western North Pacific

Based on the temperature and salinity from the Argo profiling floats and altimeter-derived geostrophic velocity anomaly (GVA) data in the western North Pacific during 2002–2011, the North Pacific Subtropical Mode Water (NPSTMW) distribution is investigated and cyclonic and anti-cyclonic eddies (CEs and AEs) are constructed to study the influence of their vertical structures on maintaining NPSTMW. Combining eddies identified by the GVA data and Argo profiling float data, it is found that the average NPSTMW thickness of AEs is about 60 dbar, which is thicker than that of CEs. The NPSTMW thicker than 150 dbar in AEs accounts for 18%, whereas that in CEs accounts for only 1%. About 3377 (3517) profiles, which located within one diameter of the nearest CEs (AEs) are used to construct the CE (AE). The composite AE traps low-PV water in the center and with a convex shape in the vertical section. The ‘trapped depth’ of the composite CE (AE) is 300 m (550 m) where the rotational velocity exceeds the transitional velocity. The present study suggests that the anticyclonic eddies are not only likely to form larger amounts of NPSTMW, but also trap more NPSTMW than cyclonic eddies.     

Super typhoon activity over the western North Pacific and its relationship with ENSO

This paper analyzes the characteristics of super typhoons(STYs)over the western North Pacific(WNP)from 1965 to2005 and describes the seasonal variability of STY activity.The relation between STY activity and the El Nio-Southern Oscillation(ENSO)as well as the possible reason for the influence of the ENSO on STY activity are also investigated.The results showed thatabout one fifth of the tropical cyclones(TCs)over the WNP could reach the rank of STY.Most STYs appeared from July to Novem-ber while there was a highest ratio between number of STYs and total number of TCs in November.Most STYs appeared east of thePhilippine Sea.In El Nio years,affected by sea surface temperature(SST),monsoon trough and weak vertical wind shear,TC for-mation locations shifted eastward and there were more STYs than in La Nia years when the affecting factors changed.     

Ventilation of the North Pacific Ocean: Water exchange between subtropical and tropical gyres

INTRODUCTIONIntheearly 1 980 s,ventilationtheoryemergedtopredictthehorizontalandverticalstructureofthethermocline.Thereweretwodifferentviewsonthestratifiedoceans.Thefirsttheory (RhinesandYoung,1 982 ,hereafterRY ;YoungandRhines,1 982 )proposedanunventilatedmodelinwhichonlytheuppermostlayerisexposedtothesurfaceandisforcedbythewindstress.Thesecondtheory (Luytenetal.,1 983 ,hereafterLPS)offeredaventilatedmodelwhichisclosertotheclassicalthermoclinetheoriesthanthatofthefirstone (e.g .,Nee…     

Response of the western North Pacific subtropical ocean to the slow-moving super typhoon Nanmadol

Based on in-situ observation, satellite and reanalysis data, responses of the western North Pacific subtropical ocean(WNPSO) to the slow-moving category 5 super typhoon Nanmadol in 2011 are analyzed. The dynamical response is dominated by near-inertial currents and Ekman currents with maximum amplitude of 0.39 m/s and 0.15 m/s, respectively. The near-inertial currents concentrated around 100 m below the sea surface and had an e-folding timescale of 4 days. The near-inertial energy propagated both upward and downward, and the vertical phase speed and wavelength were estimated to be 5 m/h and 175 m, respectively. The frequency of the near-inertial currents was blue-shifted near the surface and redshifted in ocean interior which may relate to wave propagation and/or background vorticity. The resultant surface cooling reaches -4.35℃ and happens when translation speed of Nanmadol is smaller than 3.0 m/s.When Nanmadol reaches super typhoon intensity, the cooling is less than 3.0℃ suggesting that the typhoon translation speed plays important roles as well as typhoon intensity in surface cooling. Upwelling induced by the slow-moving typhoon wind leads to typhoon track confined cooling area and the right-hand bias of cooling is slight. The mixed layer cooling and thermocline warming are induced by wind-generated upwelling and vertical entrainment. Vertical entrainment also led to mixed layer salinity increase and thermocline salinity decrease, however, mixed layer salinity decrease occurs at certain stations as well. Our results suggest that typhoon translation speed is a vital factor responsible for the oceanic thermohaline and dynamical responses, and the small Mach number(slow typhoon translation speed) facilitate development of Ekman current and upwelling.     

A new species of Nassarius (Gastropoda: Nassariidae) from the western Pacific Ocean

This paper describes a new species of Nassarius from the South China Sea,which was recognized when re-sorting the collection of Nassariidae in the Marine Biological Museum,Chinese Academy of Sciences,Qingdao,China.The shells were collected during several investigations,including the National Comprehensive Oceanic Survey in 1958-1959,and the China-Vietnam Co-Investigation on Marine Resource of the Beibu Gulf during 1959-1962.The morphology of the shell and the radula places the new species of Nassarius within the subgenus Zeuxis.It is named Nassarius(Zeuxis) nanhaiensis sp.nov.     

A THREE-LAYER OCEAN CIRCULATION MODEL APPLICATION TO NUMERICAL STUDIES ON THE NORTH PACIFIC OCEAN CIRCULATION

The formulation and justification of a three-layer baroclinic ocean model developed to simulate thegeneral circulation of the ocean are described in this paper.Test of the model in simulating the annualmean circulation patterns in the North Pacific under the prescribed atmospheric forcing,which consists ofthe climatological surface wind stress and sea surface heat flux,and comparison of the results withobservations showed that the model basically simulated the large scale features of the annual meancirculation patterns in the North Pacific Ocean such as those of the intensified western boundary currentsand the North Equatorial Currents and Undercurrents.But due to the coarse resolution of the model,some details of these currents were poorly reproduced.The seasonal variations of the North Pacific Oceancirculation driven by the seasonal mean sea surface wind stress was calculated,the different aspects of theseresults were analyzed and the main current(the intensified western boundary currents)transports we     

Deep-sea coral evidence for dissolved mercury evolution in the deep North Pacific Ocean over the last 700 years

The ocean is an important inventory of anthropogenic mercury(Hg),yet the history of anthropogenic Hg accumulation in the ocean remains largely unexplored.Deep-sea corals are an emerging archive of past ocean chemistry,which take in sinking or suspended particulate organic matter as their food sources.Such organic matter would exchange Hg with the local seawater before being consumed by the deepsea corals.As such,the organics preserved in the coral skeleton may record the Hg evolution of the ambient seawater during the time of coral growth.Here,we report the first data on Hg concentrations variability of a deep-sea proteinaceous coral in the oligotrophic North Pacific at the water depth of 1 249 m,in attempt to understand the transfer of anthropogenic Hg into the deep Pacific ocean over the last seven centuries.We find that the Hg concentrations of different coral growth layers have remained relatively constant albeit with considerable short-term variability through time.The overall stable Hg concentration of the last seven centuries recorded in our sample suggests that anthropogenic pollution is not yet a clearly resolvable component in the deep oligotrophic North Pacific waters,in agreement with rece nt estimation from modelling works and observational studies of modern seawater profiles.As there is hardly an unambiguous way to separate anthropogenic Hg from the natural background based on recent seawater profiles,our historical data provide valuable information helping to understand the oceanic cycle of Hg through time.     

西北太平洋上层海洋对连续多个台风的响应

【目的】研究Merantia、Malaks、Megi、Chaba4个连续台风引起上层海洋的响应。【方法】基于遥感和再分析数据,分析台风前海洋环境、台风做功(W)、强迫时间(tf)、降水等要素分布特征,探讨上层海洋稳定度、上升流、湍流混合动力机制如何影响中尺度涡区域的海表温度(SST)、浮游植物繁殖程度,引入动力学参数S判断海洋内部上升流和混合重要性。【结果和结论】冷涡(CE)区域海洋表层降温(SSC)(3.5℃)和叶绿素a(Chl-a)质量浓度(0.5mg/m3)对于台风响应比暖涡(AE)区更为剧烈,与其内部热力学结构有关,出现在Megi过境CE区,主要原因是海洋本身CE特征、强上升流(EPV)=2.5×10-4 m/s,S<1,台风向海洋输入巨大的能量(W>80 kJ)引起剧烈的混合夹卷、强降雨,导致海水迅速重新层化、逐渐加强的非线性CE有更强的封闭性,这些机制的共同作用将底层(营养盐跃层100m以下)富含营养盐的冷水输送到上层;Malaks过境CE(124.9°E,22.3°N)缺乏强上升流(EPV=5×10-5 m/s),以湍流混合为主(S>1);Merantia使CE区域表现下沉流(EPV<0),SSC主要是湍流混合的作用(W>25kJ),Chl-a浓度增长到0.27mg/m3。AE热力学结构比较稳定,连续台风导致SSC<2℃,Chl-a增加仅200%,Merantia、Malaks过境AE(125.1°E,20.6°N)分别以强上升流(S<1)和湍流混合(S>1)为主,混合层厚度约80 m,同时AE周围无强障碍带,易与周围水体交换,Chl-a浓度微弱增加。