Characteristics of Semi-diurnal Internal Tides in the Western Equatorial Pacific Ocean Around 1°45′S,156°E

The analyses of a data series obtained during TOGA- COARE show the existence of remarkable semi-diurnal intemal tides in the western equatorial Pacific Ocean around 1°45＇S, 156°E. Some characteristic parameters of the internal tides are vertical wavenumber -1.6×10^-3 m^-1, horizontal wavenumber （wavelength） 3.3×10^-2 km^-1 （210 km）, vertical propagation speed -3.8 cm/s and horizontal propagation speed 2.0 m/s. The waveforms propagate downwards slantingly, that is, the wave energy transfers upwards slantingly. Depth-distribution of the＇rotary spectral levels is a saddle-shape. The depths of the trough and the deeper peaks are almost coincident with those of the south boundaries of the South Equatorial Current and the Equatorial Undercurrent, respectively. The mean orientation of the rotary spectral ellipse changes with depth： 30° from north to east at 40 m, and changes into 14° from east to south at 324 m, and generally, it points to northeastward, which indicates ＂that waves come from the southwest.

Impacts of monsoon break events in the western North Pacific on the cross-equatorial flows over the Maritime Continent

本文利用ERA5逐日再分析资料,探讨了1979-2020年间西北太平洋季风中断事件对海洋性大陆越赤道气流的影响.合成结果表明,西北太平洋季风中断事件会造成高,低空越赤道气流减弱,即高层南风异常,低层北风异常,与此相关的环流异常表现为西北太平洋高层气旋,低层反气旋的斜压结构。特别的是,西北太平洋季风中断对高空越赤道气流的影响更为显著,92%的季风中断事件都导致高空越赤道气流减弱,而只有70%的事件造成低空越赤道气流减弱,这是由于低空越赤道气流同时还受到赤道中东太平洋海温异常的调控.

Dispersion relation of internal waves in thewestern equatorial Pacific Ocean

Based mainly on TOGA-COARE data, that is, the CTD data from R/V Xiangyanghong No. 5 (Pu et al., 1993), the temperature and current data from the Woods Hole mooring and other deep current data, the layered numerical profiles of buoyancy frequency and mean current components are figured out. A numerical method calculating internal wave dispersion relation without background shear current, used by Fliegel and Hunkins (1975), is improved to be fit for the internal wave equation with mean currents and their second derivatives. The dispersion relations and wave functions of the long crested internal wave progressing in any direction can be calculated conveniently by using the improved method. A comparison between the calculated dispersion relation in the paper and the dispersion relation in GM spectral model of ocean internal waves (Garret and Munk, 1972) is performed. It shows that the mean currents are important to the dispersion relation of internal waves in the western equatorial Pacific Ocean and that the currents make the wave progressing co-directional with (against) the currents stretched (shrink). The influence of the mean currents on dispersion relation is much stronger than that of their second derivatives, but that on wave function is less than that of their second derivatives. The influences on wave functions result in the change of vertical wavenumber, that is, making the wave function stretch or shrink. There exists obvious turning depth but no significant critical layer absorption is found.

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.

A Study of SST Warming Trend in the Western Equatorial Pacific in a Coupled Ocean-Atmosphere-Land GCM

In a version of LASG coupled ocean-atmosphere-land system model, where a diurnal cycle of solar radiation is included, a rapid SST warming trend of about 2.0℃ appears in the western equatorial Pacific within the first two years of an integration. An analysis reveals that the appearance of the surface westerly wind anomaly since the fifth month of the integration is responsible for the SST warming. To reduce the SST warming, the reference heat flux used in the model is then redefined according to the first 4 months, instead of the first 3 years, of a trial run. It is found that the refining of the reference heat flux is successful in avoiding the unrealistic persistent westerly wind anomaly. Consequently, the SST warming is almost completely removed. It is explored that the persistent westerly wind anomaly is induced by the anomalous surface pressure patterns in the northern tropical and subtropical regions, which is related to the errors in the surface heat flux in the off-equatorial regions.

The multifractal characters of temperature finestructuresin the equatorial western Pacific Ocean

By using part of CTD data collected at 2°S, 155° E during the fall cruise of TOGA project in 1992, themultifractal characters of temperature finestructures are investigated. The absolute temperature gradients are supposedto be multifractal and their moments are computed by conventional box-counting method. It is found that these moments have power dependence on the box size. This power dependence has two different scaling regimes, called Sregime and I-regime resistively, with different scaling exponents. This is consistent with the combined effects of internal waves and boxing. Accordingly, the generalized fractal dimensions (Renyi dimension) of temperature gradientsare derived. A nonlinear curve of the scaling exponents suggest a possible multifractal approach of the temperatureshear. In fact, both regimes can be approximated by Besicovitch- Cantor model, respectively, by suitably chosenmoduel parameters. A phenomenological model is developed on the basis of this two-regime mechanism. The model iscompared with field data and good agreement is achieved.

Indo-Western Pacific Ocean Capacitor and Coherent Climate Anomalies in Post-ENSO Summer: A Review

ENSO induces coherent climate anomalies over the Indo-western Pacific, but these anomalies outlast SST anomalies of the equatorial Pacific by a season, with major effects on the Asian summer monsoon. This review provides historical accounts of major milestones and synthesizes recent advances in the endeavor to understand summer variability over the Indo-Northwest Pacific region. Specifically, a large-scale anomalous anticyclone （AAC） is a recurrent pattern in post-E1 Nifio summers, spanning the tropical Northwest Pacific and North Indian oceans. Regarding the ocean memory that anchors the summer AAC, competing hypotheses emphasize either SST cooling in the easterly trade wind regime of the Northwest Pacific or SST warming in the westerly monsoon regime of the North Indian Ocean. Our synthesis reveals a coupled ocean- atmosphere mode that builds on both mechanisms in a two-stage evolution. In spring, when the northeast trades prevail, the AAC and Northwest Pacific cooling are coupled via wind-evaporation-SST feedback. The Northwest Pacific cooling persists to trigger a summer feedback that arises from the interaction of the AAC and North Indian Ocean warming, enabled by the westerly monsoon wind regime. This Indo-western Pacific ocean capacitor （IPOC） effect explains why E1 Nifio stages its last act over the monsoonal Indo-Northwest Pacific and casts the Indian Ocean warming and AAC in leading roles. The IPOC displays interdecadal modulations by the ENSO variance cycle, significantly correlated with ENSO at the turn of the 20th century and after the 1970s, but not in between. Outstanding issues, including future climate projections, are also discussed.

An extended variable-grid global ocean circulation model and its preliminary results of the equatorial Pacific circulation

To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is developed. Numerical computation of the annually cyclic circulation fields is performed. The results of the annual mean zonal currents and deep to abyssal western boundary currents in the equatorial Pacific Ocean are reported. The North Equatorial Current,the North Equatorial Countercurrent, the South Equatorial Current and the Equatorial Undercurrent are fairly well simulated. The model well reproduces the northward flowing abyssal western boundary current.From the model results a lower deep western boundary current east of the Bismarck-Solomon-New Hebrides Island chain at depths around 2 000 m has been found. The model results also show that the currents in the equatorial Pacific Ocean have multi-layer structures both in zonal currents and western boundary currents, indicating that the global ocean overturning thermohaline circulation appears of multi-layer pattern.

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 0.39m/s and 0.15m/s,respectively.The near-inertial currents concentrated around 100m 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 5m/h and 175m,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 3.0m/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.

Spring Indian Ocean–Western Pacific SST Contrast and the East Asian Summer Rainfall Anomaly

studying the relationship between SST in the tropical Indian Ocean （TIO）, tropical western Pacific （TWP）, and tropical eastern Pacific （TEP） and East Asian summer rainfall （EASR）, using data provided by NOAA/OAR/ESRL PSD and the National Climate Center of China for the period 1979-2008, an index, SSTDI, was defined to describe the SST difference between the TIO and TWP. In comparison with the winter ENSO, the spring SST contrast between the TIO and TWP was found to be more significantly associated with summer rainfall in East Asia, especially along the EASR band and in Northeast China. This spring SST contrast can persist into summer, resulting in a more significant meridional teleconnection pattern of lower-tropospheric circulation anomalies over the western North Pacific and East Asia. These circulation anomalies are dynamically consistent with the summer rainfall anomaly along the EASR band. When the SSTDI is higher （lower） than normal, the EASR over the Yangtze River valley, Korea, and central and southern Japan is heavier （less） than normal. The present results suggest that this spring SST contrast can be used as a new and better predictor of EASR anomalies.

Noble Gas Isotopic Compositions of Cobalt-rich Ferromanganese Crusts from the Western Pacific Ocean and Their Geological Implications

Noble gas isotopic compositions of various layers in three-layered （outer, porous and compact layers） cobalt-rich ferromanganese crusts and their basaltic and phosphorite substrates from the western Pacific Ocean were analyzed by using a high vacuum gas mass spectrum. The analytical results show that the noble gases in the Co-rich crusts have derived mainly from the ambient seawater, extraterrestrial grains such as interplanetary dust particles （IDPs） and wind-borne continental dust grains, and locally formation water in the submarine sediments, but different noble gases have different sources. He in the crusts derives predominantly from the extraterrestrial grains, with a negligible amount of radiogenic He from the eolian dust grains. Ar is sourced mainly from the dissolved air in the seawater and insignificantly from radiogenic Ar in the eolian continental dust grains or the formation water. Xe and Ne derive mainly from the seawater, with minor amounts of extraterrestrial Xe and Ne in the IDPs. Compared with the porous and outer layers, the compact layer has a relatively high 4He content and lower 3He/4He ratios, suggesting that marine phosphatization might have greatly modified the noble gas isotopic compositions of the crusts. Besides, the 3He/4He values of the basaltic substrates of the cobalt-rich crusts are very low and their R/R. ratios are mostly 〈0.1 R., which are similar to that of phosphorite substrates （0.087 R.）, but much lower than that of fresh submarine MORB （8.75±14 Ra） or seamount basalts （3-43 Ra）, implying that the basaltic substrates have suffered strong water/rock interaction and reacted with radiogenic ^4He and P-rich upwelling marine currents during phosphatization. The trace elements released in the basalt/seawater interaction might favor the growth of cobalt-rich crusts. The relatively low ^3He/^4He values in the seamount basalts may be used as an important exploration criterion for the cobalt-rich ferromanganese crusts.

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.

Physical oceanography of the Caroline M4 seamount in the tropical Western Pacific Ocean in summer 2017

Physical oceanography plays an important role in the formation of submarine sediments,and the distribution of nutriments and biocenoses in seamounts.The M4 seamount is located in the Caroline Island Ridge of the Western Pacific Ocean.The physical properties around M4 seamount are preliminarily analyzed based on the in-situ data obtained in summer 2017 in Caroline M4 seamount and open-sourced data.We found that the water in the upper 200 m is controlled by the westward North Equatorial Current(NEC),while the water between 300-1000 m is dominated by the eastward North Equatorial Undercurrent(NEUC).The current direction fluctuates significantly below 300 m at upstream stations.At the same depth of the lee sides,the current direction changes with the distance from seamount.These are likely caused by the obstacle of M4 seamount.The calculation results show that there is an anticyclonic cap above M4 seamount caused by tidal rectification.Tidal currents in M4 seamount are squeezed by the topography and amplified,and the amplified tidal currents play a dominant role in M4 seamount.First,the circulation system generated by the interaction of the amplified tidal current and M4 seamount drives the upward/downward movement of the isotherms.Secondly,the thickness of the surface turbulent layer is changed with the tidal phase.Thirdly,high turbulent diffusivities are found in the bottom of M4 seamount,and these are most likely attributed to the turbulent mixing induced by the mutual effect between semidiurnal tidal currents and steep bathymetry.This article of physical oceanography provides scientific basis for further analysis of the distribution of biological community and deposition mechanism in M4 seamount.

Geochemical characteristics of sediments from the COMRA registered pioneer area (CRPA),equatorial northeastern Pacific Ocean

COMRA(China Ocean Mineral Resources Association) registered pioneer area (CRPA) is located in the western part of the area between the Clarion and Clipperton Fraction Zones (CCFZs). Based on distinctive color and bio-disturbing properties, two layers are recognized in the sediment columns from the CRPA: a pale brown layer (Unit A) on the top and a dark for layer (Unit B) in the lower part. Color division between them can be explained as a hiatus. As a resu1t, the two units are different to each other in chemical composition and sediment properties. It is found that contents of P2O5, MnO2, CaO, Na2O in sediments of older Unit B are higher, but SiO2 content is slightly lower. Based on correlation analysis, Mn and Fe in the sediments have different origins. The former is mainly precipitated in authigenic process, whilst the latter is closely related to terrigenous detritus. Therefore, the differences in chemical composition of the sediments are caused by different sedimentation settings.

Control factors of DIC in the Y3 seamount waters of the Western Pacific Ocean

An investigation was carried out in the Y3 seamount area of the Western Pacific Ocean in December 2014,and the distribution of dissolved inorganic carbon(DIC)and its relationship with environmental factors in this area were explored.The results show that DIC concentration was higher in the adjacent waters of the Y3 seamount area,and the uplift of DIC isolines at the stations was close to the seamount.Meanwhile,interaction between the North Equatorial Current(NEC)and the Y3 seamount affected the DIC distribution,i.e.,the upwelling in the same direction of the NEC was obvious,resulting in a decreasing trend of average concentration of DIC in the 200 m water column from the top to the two sides in this direction but in the cross direction.The DIC concentration increased with the water depth increase,and its distribution was affected by various environmental factors.In the surface water,high temperature was a decisive factor for the decrease of the DIC concentration,but the photosynthesis of phytoplankton showing only a weak influence.In the North Pacific Tropic Water(NPTW),DIC production rate from organic matter decomposition was higher than that of DIC consumption by phytoplankton photosynthesis,leading to a continual increase of DIC.In the North Pacific Intermediate Water(NPIW),organic matter decomposition played a leading role in the increase of DIC.In the deep water,decomposition of organic matter weakened,and the dissolution of CaCO3 controlled the carbonate system,and DIC had the smallest variation range.

Tracking typhoon-generated swell in the western North Pacific Ocean using satellite altimetry

This paper proposes a scheme for detecting the swell decay of a moving typhoon. We considered a typhoon that was neither far from a point source nor had a belt-like homogenous source,as previously studied. We tracked the swell close to the source during a typhoon in the western North Pacific Ocean. We used wind speed and significant wave height data derived from the Geophysical Data Record of the Jason-1 altimeter and the best-track information of the typhoon from the China Meteorological Administration tropical cyclone database. We selected three specific cases to reveal the decay characteristics of the swell generated by a moving typhoon. Based on an altimeter-based typhoon swell identification scheme and the dispersion relationship for deep water,we relocated the swell source for each altimeter measurement. The subsequent statistical decay coefficient was comparable to previous studies,and effectively depicted the swell propagation conditions induced by the typhoon. We hope that our results provide a new understanding of the characteristics and wave energy budget of the North Pacific Ocean,and significantly contribute to wave modeling in this region.

Planktonic ciliate trait structure variation over Yap,Mariana,and Caroline seamounts in the tropical Western Pacific Ocean

Trait structure is increasingly used in plankton ecology to understand diversity and biogeography.However,our knowledge of micro zooplankton(e.g.planktonic ciliates)trait structure and its variation with hydrography is limited.In this study,we analyzed planktonic ciliate trait structure in waters with different hydrography and deep Chlorophyll a maximum(DCM)layers over three seamounts:Yap,Mariana,and Caroline seamounts.Mariana seamount had a lower surface temperature than the Yap and Caroline seamounts.DCM layers over Mariana and Caroline seamounts were deeper than Yap seamount.There was a weak upwelling in upper 50 m around top of Mariana seamount.The ciliate distribution showed bimodal pattern(high abundance appeared in the surface and DCM layers)over three seamounts.At surface layer,the large size-fraction(>30μm)abundance proportion to aloricate ciliate over Yap seamount(44.4%)was higher than Mariana(32.8%)and Caroline(36.1%)seamounts.For tintinnid abundance proportion to total ciliate,Mariana(12.0%)and Caroline(11.5%)seamounts at about 100-m depth were higher than that of Yap seamount(6.4%).Vertically,tintinnid could be divided into 4 groups over the three seamounts.At30-m depth,group I(species occurring from surface to 100 m only)was dominant component over Yap and Caroline seamounts,while group IV(species occurring at every depth)changed into dominant component over Mariana seamount,the weak upwelling might be the reason.Salpingella faurei was the top dominant species,which corresponded to deeper DCM layers over Mariana and Caroline seamounts.Our results showed that the upwelling and the deeper DCM could influence the planktonic ciliate trait structure.

Bottom water temperature measurements in the South China Sea,eastern Indian Ocean and western Pacific Ocean

文章报道了一批新的海底底水温度(BWT)数据,其中南海(SCS)158个站位、东印度洋(EIO)30个站位及西太平洋(WPO)37个站位。基于这批新的BWT数据,获得南海和西太平洋海域底水温度与水深经验关系,可为地球物理和物理海洋提供准确、可靠的海底温度边界。这将有助于海底油气资源调查与评估。同时,这批实测数据表明:1)水深超过3500m的海域,其底水温度在南海约为2.47℃,比东印度洋(～1.34℃)和西太平洋(～1.60℃)稍微偏高。这与大洋传送带模式所预测的情况比较吻合。该模式认为:低温高盐的海水,从北大西洋格陵兰岛和冰岛附近海域下沉到深层,然后向南流动,再与南极洲周围海域的低温高盐海水一同向北进入印度洋和太平洋。而南海是一个相对比较封闭的热带边缘海,其内部海水与印度洋和菲律宾海交换有限,导致海水温度整体高于印度洋和太平洋。2)台西南盆地水深在2700～3000m的部分站位,其底水温高达约3.00℃,明显高于其周边同水深海域底水温度(平均值约为2.33℃)。这可能是台西南盆地海底水热活动导致的结果。3)在东印度洋和西太平洋水深超过4800m海域,底水温度随着水压增大稍有升高,其升高率分别为10.6mK·MPa^(-1)和12.0mK·MPa^(-1)。这与理论估算的深层底水绝热压力温度梯度范围较为吻合。这也意味着东印度洋和西太平洋深层底水,主要由绝热自压作用导致其温度随着深度的增大而升高。

ROLE OF EQUATORIAL PACIFIC OCEAN SUBSURFACE OCEANIC TEMPERATURE MODE IN ENSO CYCLE

Based on the simple ocean data assimilation(SODA) reanalysis dataset from the University of Maryland and the method of Empirical Orthogonal Functions(EOF),the characteristics of interannual and interdecadal variabilities of the equatorial Pacific subsurface oceanic temperature anomaly(SOTA) are captured.The first and second modes of the equatorial Pacific SOTA in the interannual and interdecadal variations are found respectively and the effect of the second mode on the ENSO cycle is discussed.Results show that the first mode of SOTA's interannual and interdecadal variabilities exhibit a dipole pattern,indicating that the warm and cold temperature anomalies appear simultaneously in the equatorial subsurface Pacific.The second mode shows coherent large-scale temperature anomalies in the equatorial subsurface Pacific,which is a dominant mode in the evolution of ENSO cycle.The temporal series of the second mode has a significant lead correlation with the Ni?o-3.4 index,which can make a precursory prediction signal for ENSO.The function of this prediction factor in SOTA is verified by composite and case analyses.

Predicting Western Pacific Subtropical High Using a Combined Tropical Indian Ocean Sea Surface Temperature Forecast

Weather and climate in East China are closely related to the variability of the western Pacific subtropical high(WPSH), which is an important part of the Asian monsoon system. The WPSH prediction in spring and summer is a critical component of rainfall forecasting during the summer flood season in China. Although many attempts have been made to predict WPSH variability, its predictability remains limited in practice due to the complexity of the WPSH evolution. Many studies have indicated that the sea surface temperature(SST) over the tropical Indian Ocean has a significant effect on WPSH variability. In this paper, a statistical model is developed to forecast the monthly variation in the WPSH during the spring and summer seasons on the basis of its relationship with SST over the tropical Indian Ocean. The forecasted SST over the tropical Indian Ocean is the predictor in this model, which differs significantly from other WPSH prediction methods. A 26-year independent hindcast experiment from 1983 to 2008 is conducted and validated in which the WPSH prediction driven by the combined forecasted SST is compared with that driven by the persisted SST. Results indicate that the skill score of the WPSH prediction driven by the combined forecasted SST is substantial.