Scientific questions about South China Sea ocean dynamics

South China Sea, its circulation and connection with other parts of the world oceans, poses important scientific questions. From the prospective view, we postulate ten key research directions to be pursued in the coming future, including ventilation of a monsoon dominated sea, water mass formation/transformation, heat/salt and water mass balance, energetics and mixing, mesoscale eddies, the role of typhoon, deep circulation and paleoclimate records, interaction with adjacent oceans, upwelling and ecology system, and response to climate changes.

Modeling and analysis of the ocean dynamic with Gaussian complex network

The techniques for oceanographic observation have made great progress in both space-time coverage and quality, which make the observation data present some characteristics of big data. We explore the essence of global ocean dynamic via constructing a complex network with regard to sea surface temperature. The global ocean is divided into discrete regions to represent the nodes of the network. To understand the ocean dynamic behavior, we introduce the Gaussian mixture models to describe the nodes as limit-cycle oscillators. The interacting dynamical oscillators form the complex network that simulates the ocean as a stochastic system. Gaussian probability matching is suggested to measure the behavior similarity of regions. Complex network statistical characteristics of the network are analyzed in terms of degree distribution, clustering coefficient and betweenness. Experimental results show a pronounced sensitivity of network characteristics to the climatic anomaly in the oceanic circulation. Particularly, the betweenness reveals the main pathways to transfer thermal energy of El Niño–Southern oscillation. Our works provide new insights into the physical processes of ocean dynamic, as well as climate changes and ocean anomalies.

The Role of Ocean Dynamics in the Cross-equatorial Energy Transport under a Thermal Forcing in the Southern Ocean

Under external heating forcing in the Southern Ocean,climate models project anomalous northward atmosphere heat transport(AHT)across the equator,accompanied by a southward shift of the intertropical convergence zone(ITCZ).Comparison between a fully coupled and a slab ocean model shows that the inclusion of active ocean dynamics tends to partition the cross-equatorial energy transport and significantly reduce the ITCZ shift response by a factor of 10,a finding which supports previous studies.To understand how ocean dynamics damps the ITCZ’s response to an imposed thermal heating in the Southern Ocean,we examine the ocean heat transport(OHT)and ocean circulation responses in a set of fully coupled experiments.Results show that both the Indo-Pacific and the Atlantic contribute to transport energy across the equator mainly through its Eulerian-mean component.However,different from previous studies that linked the changes in OHT to the changes in the wind-driven subtropical cells or the Atlantic meridional overturning circulation(AMOC),our results show that the cross-equatorial OHT anomaly is due to a broad clockwise overturning circulation anomaly below the subtropical cells(approximately bounded by the 5°C to 20°C isotherms and 50°S to 10°N).Further elimination of the wind-driven component,conducted by prescribing the climatological wind stress in the Southern Ocean heat perturbation experiments,leads to little change in OHT,suggesting that the OHT response is predominantly thermohaline-driven by air-sea thermal interactions.

The tropical Pacific cold tongue mode and its associated main ocean dynamical process in CMIP5 models

The cold tongue mode(CTM),which represents the out-of-phase relationship in sea surface temperature anomaly(SSTA)variability between the Pacific cold tongue region and elsewhere in the tropical Pacific,shows a long-term cooling trend in the eastern equatorial Pacific.In this study,we investigate how well the CTM is reproduced in historical simulations generated by the 20 models considered in Phase 5 of the Coupled Model Intercomparison Project(CMIP5).Qualitatively,all 20 models roughly capture the cooling SSTA associated with the CTM.However,a quantitative assessment(i.e.,Taylor diagrams and the ratio of the trend between the simulations and observations)shows that only five of these 20 models(i.e.,CESM1-CAM5,CMCC-CM,FGOALS-g2,IPSL-CM5B-LR,and NorESM1-M)can reproduce with useful accuracy the spatial pattern and long-term trend of the CTM.We find that these five models generally simulate the main ocean dynamical process associated with the CTM.That is,these models adequately capture the long-term cooling trend in the vertical advection of the anomalous temperature by the mean upwelling.We conclude that the performance of these CMIP5 models,with respect to simulations of the long-term cooling trend associated with the vertical advection,and the related long-term decreasing trend of the vertical gradient of the oceanic temperature anomaly,can play an important role in successful reproduction of the CTM.

ESTABLISHMENT OF THE OCEAN DYNAMIC SYSTEM WITH FOUR SUB-SYSTEMS AND THE DERIVATION OF THEIR GOVERNING EQUATION SETS

Based on their differences in physical characteristics and time-space scales,the ocean motions have been divided into four types in the present paper：turbulence,wave-like motion,eddy-like motion and circulation.Applying the three-fold Reynolds averages to the governing equations with Boussinesq approximation,with the averages defined on the former three sub-systems,we derive the governing equation sets of the four sub-systems and refer to their sum as ＂the ocean dynamic system＂.In these equation sets,the interactions among different motions appear in two forms：the first one includes advection transport and shear instability generation of larger scale motions,and the second one is the mixing induced by smaller scale motions in the form of transport flux residue.The governing equation sets are the basis of analytical/numerical descriptions of various ocean processes.

Upper-Ocean Dynamical Features and Prediction of the Super El Nino in 2015/16:A Comparison with the Cases in 1982/83 and 1997/98

The 2015/16 super El Ni？o event has been widely recognized as comparable to the 1982/83 and 1997/98 El Ni？o events.This study examines the main features of upper-ocean dynamics in this new super event,contrasts them to those in the two historical super events,and quantitatively compares the major oceanic dynamical feedbacks based on a mixed-layer heat budget analysis of the tropical Pacific.During the early stage,this new event is characterized by an eastward propagation of SST anomalies and a weak warm-pool El Ni？o;whereas during its mature phase,it is characterized by a weak westward propagation and a westward-shifted SST anomaly center,mainly due to the strong easterly wind and cold upwelling anomalies in the far eastern Pacific,as well as the westward anomalies of equatorial zonal current and subsurface ocean temperature.The heat budget analysis shows that the thermocline feedback is the most crucial process inducing the SST anomaly growth and phase transition of all the super events,and particularly for this new event,the zonal advective feedback also exerts an important impact on the formation of the strong warming and westward-shifted pattern of SST anomalies.During this event,several westerly wind burst events occur,and oceanic Kelvin waves propagate eastwards before being maintained over eastern Pacific in the mature stage.Meanwhile,there is no evidence for westward propagation of the off-equatorial oceanic Rossby waves though the discharging process of equatorial heat during the development and mature stages.The second generation El Ni？o prediction system of the Beijing Climate Center produced reasonable event real-time operational prediction during 2014–16,wherein the statistical prediction model that considers the preceding oceanic precursors plays an important role in the multi-method ensemble prediction of this super.

Ocean dynamic noise energy flux directivity in the 400 Hz to 700 Hz frequency band

Results of field studies of underwater dynamic noise energy flux directivity at two wind speeds, 6 m/s and 12 m/s, in the 400 Hz to 700 Hz frequency band in the deep open ocean are presented. The measurements were made by a freely drifting telemetric combined system at 500 m depth. Statistical characteristics of the horizontal and vertical dynamic noise energy flux directivity are considered as functions of wind speed and direction. Correlation between the horizontal dynamic noise energy flux direction and that of the wind was determined; a mechanism of the horizontal dynamic noise energy flux generation is related to the initial noise field scattering on ocean surface waves.

Effect of wind stress forcing on ocean dynamics at air-sea interface

We evidence and study the differences in turbulence statistics in ocean dynamics carried by wind forcing at the air-sea interface. Surface currents at the air-sea interaction are of crucial importance because they transport heat from low to high latitudes. At first order, oceanic currents are generated by the balance of the Coriolis and pressure gradient forces(geostrophic current) and the balance of the Coriolis and the frictional forces dominated by wind stress(Ekman current) in the surface ocean layers. The study was conducted by computing statistical moments on the shapes of spectra computed within the framework of microcanonical multi-fractal formalism. Remotely sensed daily datasets derived from one year of altimetry and wind data were used in this study, allowing for the computation of two kinds of vector fields: geostrophy with and geostrophy without wind stress forcing. We explore the statistical properties of singularity spectra computed from velocity norms and vorticity data, notably in relation with kurtosis information to underline the differences in the turbulent regimes associated with both kinds of velocity fields.

Heat coma as an indicator of resistance to environmental stress and its relationship to ocean dynamics in the sea skaters, Halobates （Heteroptera： Gerridae）

The tolerance to temperature increase was tested for Halobates individuals collected during two cruises in the western tropical Pacific Ocean （MR-06-05-Leg 3, December 21, 2006-January 12, 2007, 0°N-8°N; KH-06-02-Leg 5, August 18-31, 2006, 12°N-17°N）. High temperature coma experiments were conducted on adults and 5th instar larvae. On average, H. sericeus （distributed in the wide latitude zone of 5°N-40°N）, H. germanus （distributed in the moderate latitude zone of 0°N-35°N） and H. micans （distributed mainly in the lower latitudes around the equator） were on average paralyzed at 35.6℃（SD： 0.89）, 32.9℃ （SD： 2.17） and 31.6℃ （SD： 2.60）, respectively （P = 0.035）. According to the current dynamics during the cruise, the colony ofH. sericeus at one station （5°N 137°E） may have been transferred from the northern area of 14°N by three currents （North Equatorial Current, Mindanao Current and North Equatorial Counter Current） to the area of 5°N 138°E. Extremely high heat resistance was shown by the adults of H. germanus in the sea area around the equator. Dynamic current and air movements in this area around the equator, that is a ＂warm seawater pool＂, could be hypothesized to be related to the high resistance to heat shown in this study.

Toward development of the 4Dvar data assimilation system in the Bering Sea:reconstruction of the mean dynamic ocean topography

The Bering Sea circulation is derived as a variational inverse of hydrographic profiles（ temperature and salinity） , atmospheric climatologies and historical observation of ocean curents. The important result of this study is estimate of the mean climatological sea surface height （SSH） that can be used as a reference for satellite altimetry sea level anomaly data in the Bering Sea region. Numerical experiments reveal that, when combined with satellite altimetry, the obtained reference SSH effectively constrains a realistic reconstruction of the Amukta Pass circulation.

The dynamical and thermodynamical analysis of the oceanic response to storm

In this paper, the discussion is made on the problem of the oceanic response caused by air-sea interaction under storm. First, the perturbation differential equations for the problem are given, and the interaction functions are supposed to be the solving conditions. Next, the nonlinear diffusion equations of the problem are solved by using the method of the given variable transforms and the specific variable power series. Finally, the response disturbances to the circular intense storm is calculated so as to discribe quantitatively the evolution processes of the oceanic response.

Recent progress in China in the study of ocean's role in climate variation

Recent （2007-2010） research results about ocean＇s role in climate variation and change by Chinese scientists are highlighted. This paper reviews a majority contributions by Chinese scientists to the understanding of ocean variability and change. This paper starts with the results about the important role of the tropical Indian Ocean in interannual variation of the Asia summer monsoon, the effect of sea surface temperature （SST） and freshwater flux on climate variability in the Pa- cific, and interannual variability research in other oceans. Then results about ocean dynamic and thermodynamic roles in decadal climate variation are reviewed. Finally, the results about, oceanic response to global warming are discussed, again showcasing ocean＇s important role in climate.

Current Status and Main Application Achievements of Ocean Satellites

Ocean satellites have realized multi-satellite networked operation.The HY-1D satellite launched in June 2020 realized networked with HY-1C satellite,and completed the construction of ocean color satellite constellation.The HY-2D satellite launched in May 2021 is networked with the on orbit HY-2B and HY-2C satellites to complete the construction of marine dynamic environment satellite constellation.The 1 mC-SAR satellite 01 launched in November 2021 is networked with GF-3,which initially forms the marine monitoring satellite constellation.This year,the networking of 1 mC-SAR satellite 02 with satellite 01 and GF-3 is realized,and the construction of marine monitoring satellite constellation is completed.At present,the ocean satellites have the operational application capabilities of remote sensing investigation,monitoring,evaluation and supervision of marine ecology,marine disaster prevention and reduction,global oceans and Polar Regions,Sea Islands,rights and interests maintenance.

Regional Characteristics of Typhoon-Induced Ocean Eddies in the East China Sea

The asymmetrical structure of typhoon-induced ocean eddies（TIOEs） in the East China Sea（including the Yellow Sea）and the accompanying air–sea interaction are studied using reanalysis products. Thirteen TIOEs are analyzed and divided into three groups with the k-prototype method： Group A with typhoons passing through the central Yellow Sea; Group B with typhoons re-entering the sea from the western Yellow Sea after landing on continental China; and Group C with typhoons occurring across the eastern Yellow Sea near to the Korean Peninsula. The study region is divided into three zones（Zones Ⅰ, Ⅱ and Ⅲ） according to water depth and the Kuroshio position. The TIOEs in Group A are the strongest and could reverse part of the Kuroshio stream, while TIOEs in the other two groups are easily deformed by topography. The strong currents of the TIOEs impact on the latent heat flux distribution and upward transport, which facilitates the typhoon development. The strong divergence within the TIOEs favors an upwelling-induced cooling. A typical TIOE analysis shows that the intensity of the upwelling of TIOEs is proportional to the water depth, but its magnitude is weaker than the upwelling induced by the topography. In Zones Ⅰ and Ⅱ, the vertical dimensions of TIOEs and their strong currents are much less than the water depths.In shallow water Zone Ⅲ, a reversed circulation appears in the lower layer. The strong currents can lead to a greater, faster,and deeper energy transfer downwards than at the center of TIOEs.

Observation and modeling of tide- and wind-induced surface currents in Galway Bay

A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model validation, the accuracy of the radar data was verified through comparison with measurements from acoustic Doppler current profilers （ADCPs） and a good correlation between time series of surface current speeds and directions obtained from radar data and ADCP data. Since Galway Bay is located on the coast of the Atlantic Ocean, it is subject to relatively windy conditions, and surface currents are therefore strongly wind-driven. With a view to assimilating the radar data for forecasting purposes, a three-dimensional numerical model of Galway Bay, the Environmental Fluid Dynamics Code （EFDC）, was developed based on a terrain-following vertical （sigma） coordinate system. This study shows that the performance and accuracy of the numerical model, particularly with regard to tide- and wind-induced surface currents, are sensitive to the vertical layer structure. Results of five models with different layer structures are presented and compared with radar measurements. A variable vertical structure with thin layers at the bottom and the surface and thicker layers in the middle of the water column was found to be the optimal layer structure for reproduction of tideand wind-induced surface currents. This structure ensures that wind shear can properly propagate from the surface layer to the sub-surface layers, thereby ensuring that wind forcing is not overdamped by tidal forcing. The vertical layer structure affects not only the velocities at the surface layer but also the velocities further down in the water column.

Application of the Three-Dimensional Shallow Sea and Continental Shelf Mode for Inversion of Undercurrent

Abstract. Due to the incapability of high frequency surface wave radar （HFSWR） to detect undercurrent parameters, a new algorithm is proposed to apply a three-dimensional （3D） nonlinear barotropic shallow sea and continental shelf model in coordinate system to the inversion of undercurrent. The calculation domain of this model is the area detected by HFSWR. Considering the benthal topography of the detected area and the ocean dynamic parameters, such as surface current, wind and wave detected by HFSWR, the relation between surface current and undercurrent is established in this model, Accordingly, the undercurrent parameters of corresponding area are obtained. The inversion results agree with the law of ocean dynamics and reproduce the movement of undercurrent.

中国海洋卫星发展现状和主要应用进展

China’s ocean satellites are divided into three series based on ocean color satellites(HY-1),ocean dynamic environment satellites(HY-2)and ocean monitoring satellites(HY-3).The three series of ocean satellites operate today in a multi-satellite network.The HY-1 D satellite launched in June 2020 and the HY-1 C satellite,already in orbit,realized a network observation capability and completed the formation of the ocean color satellite constellation.The HY-2 D satellite launched in May 2021 joined the HY-2 B and HY-2 C satellites,which have been on orbit already and completed a network observation capability,thus establishing the ocean dynamic environment satellite constellation.The GF-302 satellite(1 m C-SAR 01)launched in November 2021 has networked with GF-3,initially establishing an ocean monitoring satellite constellation,which has finally completed its construction with the launch of the GF-303 satellite(1 m C-SAR 02)in April 2022.The GF-3 three-satellite network effectively boasts a wide capability in applications of satellite data products and services in many fields,such as ocean environmental monitoring,ocean disaster prevention and mitigation,marine scientific research and polar research.

The Application of ARGO Data to the Global Ocean Data Assimilation Operational System of NCC

In this paper, we have preliminarily studied the application of ARGO (Arrayfor Real-time Geostrophic Oceanography) data to the Global Ocean Data Assimilation System ofNational Climate Center of China (NCC-GODAS), which mainly contains 4 sub-systems such as datapreprocessing, real-time wind stress calculating, variational analysis and interpolating, and oceandynamic model. For the sake of using ARGO data, the relevant adjustment and improvement have beenmade at the corresponding aspects in the subsystems. Using the observation data from 1981 to 2003including the ARGO data of 2001 to July. 2003, we have performed a series of numerical experimentson this system. Comparing with the corresponding results of NCEP, It is illustrated that using ARGOdata can improve the results of NCC-GODAS in the region of the Middle Pacific, for instance SST,SSTA (SST anomalies), Nino index, sea sub-surface temperature, etc. Furthermore, it is obtained thatNCC-GODAS benefits from ARGO data in the other regions such as Atlantic Ocean, Indian Ocean, andextratropical Pacific Ocean much more than in the tropical Pacific.