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Leading modes of interannual variability in upper-ocean salinity in the tropical Indian Ocean (TIO) and their connections were studied based on 17 years (2002–18) of oceanic historical and reanalysis data. Empirical orthogonal function (EOF) analysis depicted the dominant roles of the first two leading modes in salinity variability in the TIO over a wide range of interannual time scales. Among the rich oscillations of the leading EOF modes, a coherent near-biennial band was identified with basinwide loading of sea surface salinity anomalies (SSSa) (EOF1) leading/lagging the northeast–southwest dipolar mode of SSSa (EOF2) by around 4 months across the TIO, with southwestward migration of SSSa center. The spatial loadings of the SSSa leading modes in the TIO were strongly shaped by sea surface temperature–related freshwater fluxes and wind-driven regional ocean circulation on a near-biennial time scale. Composite analysis of the mixed layer salinity budget reflected characteristic features of basin-scale ocean–atmosphere coupling, both temporally and regionally during the life cycle of the near-biennial fluctuation in anomalous salinity in the TIO. Consistent with the intrinsic oscillation paradigm in the observed Indian Ocean dipole (IOD) variation, the dynamic and thermodynamic feedbacks associated with switches from the positive to negative IOD modes provided the phase-connection mechanisms for the SSSa leading-mode displacement over the TIO. Significance Statement This study investigates the leading modes of interannual variability in upper-ocean salinity in the tropical Indian Ocean (TIO). The intrinsic oscillation and associated dynamic and thermodynamic feedbacks over the TIO drive the basinwide connections of upper-ocean salinity variability. Our results show that a coherent near-biennial band is identifiable within the leading modes of sea surface salinity anomalies (SSSa), in which the wind-induced horizontal advections and evaporation-minus-precipitation anomalies associated with the switches from positive to negative Indian Ocean dipole modes mainly provide the phase-transition mechanism of SSSa. This research illustrates substantial evidence for the displacement of basin-scale sea surface temperature anomalies modulating the structures of SSSa and inducing the dynamical connections of leading modes of SSSa on the near-biennial time scale.

The interannual variability of summertime eddy-induced heat transport (EHT) in the western South China Sea (WSCS) is investigated based on the downgradient eddy diffusivity method and explored its formation mechanism. Estimations of long-term mean EHT and its monthly evolution reveal that the largest EHT in the SCS occurs in the WSCS region during the summer. In the WSCS, enhanced EHT and eddy kinetic energy (EKE) levels are simultaneously observed in 1994, 1999, 2002, 2006, 2008, 2009, 2012, 2014 whereas the lower EHT and EKE levels are observed in 1995, 2000, 2001, 2003, 2004, 2007, 2010, 2015, 2017 during JAS (July, August and September) months. Analysis of the Simple Ocean Data Assimilation, version 3.3.1 (SODAv3) data along 110.75° E reveals a strong surface intensification of the summertime eastward jet (SEJ) in the EHT-strong years than the EHT-weak years. Linear stability analysis conducted by adopting a 2 ½-layer reduced gravity model shows that the increased EHT in EHT-strong years is due to the enhanced baroclinic instability caused by the strong vertical shear developed through the surface-intensification of SEJ. The cause for the interannually varying vertical shear can be sought in the interannually varying meridional temperature gradient which is influenced by the combined forcing of the meridional Ekman flux convergence, meridional geostrophic flux convergence, and convergence of the latitudinally dependent surface heat flux forcing. It is also found that the interannual variations of EHT in the SCS are partially influenced by the local wind stress curl and remote forcing from the eastern boundary.

The first baroclinic mode Rossby wave is known to be of critical importance to the annual sea level variability in the southern tropical Indian Ocean (STIO; 0°–20°S, 50°–115°E). In this study, an analysis of continuously stratified linear ocean model reveals that the second baroclinic mode also has significant contribution to the annual sea level variability (as high as 81% of the first baroclinic mode). The contributions of residual high-order modes (3 ≤ n ≤ 25) are much less. The superposition of low-order (first and second) baroclinic Rossby waves (BRWs) primarily contribute to the high energy center of sea level variability at ~10°S in the STIO and the vertical energy penetration below the seasonal thermocline. We have found that 1) the low-order BRWs, having longer zonal wavelengths and weaker damping, can couple more efficiently to the local large-scale wind forcing than the high-order modes and 2) the zonal coherency of the Ekman pumping results in the latitudinal energy maximum of low-order BRWs. Overall, this study extends the traditional analysis to suggest the characteristics of the second baroclinic mode need to be taken into account in interpreting the annual variability in the STIO.

Research on the diffusion characteristics of swells contributes positively to wave energy forecasting, swell monitoring, and early warning. In this work, the South Indian Ocean westerly index (SIWI) and Indian Ocean swell diffusion effect index (IOSDEI) are defined on the basis of the 45-year (September 1957–August 2002) ERA-40 wave reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) to analyze the impact of the South Indian Ocean westerlies on the propagation of swell acreage. The following results were obtained: 1) The South Indian Ocean swell mainly propagates from southwest to northeast. The swell also spreads to the Arabian Sea upon reaching low-latitude waters. The 2.0-meter contour of the swell can reach northward to Sri Lankan waters. 2) The size of the IOSDEI is determined by the SIWI strength. The IOSDEI requires approximately 2–3.5 days to fully respond to the SIWI. The correlations between SIWI and IOSDEI show obvious seasonal differences, with the highest correlations found in December–January–February (DJF) and the lowest correlations observed in June–July–August (JJA). 3) The SIWI and IOSDEI have a common period of approximately 1 week in JJA and DJF. The SIWI leads by approximately 2–3 days in this common period.

False content in microblogs affects users’ judgment of facts. An evaluation of microblog content credibility can find false information as soon as possible, which ensures that social networks maintain a positive environment. The influence of sentiment polarity can be used to analyze the correlation between sentiment polarity in comments and Weibo content through semantic features and sentiment features in comments, to improve the effect of content credibility assessment. This paper proposes a Weibo content credibility evaluation model, CEISP (Credibility Evaluation based on the Influence of Sentiment Polarity). The semantic features of microblog content are extracted by a bidirectional-local information processing network. Bidirectional long short-term memory (BiLSTM) is used to mine the sentiment features of comments. The attention mechanism is used to capture the impact of different sentiment polarities in comments on microblog content, and the influence of sentiment polarities is obtained for the credibility assessment of microblog content. The experimental results on real datasets show that the evaluation performance of the CEISP model is improved compared with the comparison model. Compared with the existing Att-BiLSTM model, the evaluation accuracy of the CEISP model is improved by 0.0167.

Topographic Rossby waves (TRWs) are reported to make a significant contribution to the deep-ocean current variability. On the northern South China Sea (NSCS) continental slope, TRWs with peak spectral energy at ~14.5 days are observed over about a year at deep moorings aligned east–west around the Dongsha Islands. The TRWs with a group velocity of O(10) cm s−1 contribute more than 40% of total bottom velocity fluctuations at the two mooring stations. The energy propagation and source are further identified using a ray-tracing model. The TRW energy mainly propagates westward along the NSCS continental slope with a slight downslope component. The possible energy source is upper-ocean 10–20-day fluctuations on the east side of the Dongsha Islands, which are transferred through the first baroclinic mode (i.e., the second EOF mode). These 10–20-day fluctuations in the upper ocean are associated with mesoscale eddies. However, to the west of the Dongsha Islands, the 10–20-day fluctuations in the upper ocean are too weak to effectively generate TRWs locally. This work provides an interesting insight toward understanding the NSCS deep current variability and the linkage between the upper- and deep-ocean currents.

By analyzing in situ observations and conducting a series of ocean general circulation model experiments, this study investigates the physical processes controlling intraseasonal variability (ISV) of the Equatorial Undercurrent (EUC) of the Indian Ocean. ISV of the EUC leads to time-varying water exchanges between the western and eastern equatorial Indian Ocean. For the 2001–14 period, standard deviations of the EUC transport variability are 1.92 and 1.77 Sv (1 Sv ≡ 106 m3 s−1) in the eastern and western basins, respectively. The ISV of the EUC is predominantly caused by the wind forcing effect of atmospheric intraseasonal oscillations (ISOs) but through dramatically different ocean dynamical processes in the eastern and western basins. The stronger ISV in the eastern basin is dominated by the reflected Rossby waves associated with intraseasonal equatorial zonal wind forcing. It takes 20–30 days to set up an intraseasonal EUC anomaly through the Kelvin and Rossby waves associated with the first and second baroclinic modes. In the western basin, the peak intraseasonal EUC anomaly is generated by the zonal pressure gradient force, which is set up by radiating equatorial Kelvin and Rossby waves induced by the equatorial wind stress. Directly forced and reflected Rossby waves from the eastern basin propagate westward, contributing to intraseasonal zonal current near the surface but having weak impact on the peak ISV of the EUC.

Oxygen has usually been considered to be detrimental for the glass formation ability and rarely been taken as a main constituent of amorphous alloys. Here, the effect of oxygen on the glass formation of electrodeposited Mo–O binary alloys was systematically investigated by regulating the current density, and the existence of oxygen was found to promote and stabilize the glassy structure. Fully amorphous structure is obtained at the composition of 76 at.% Mo and 24 at.% O, which is close to the Mo–O binary eutectic point. With an increase in the current density from 0.4 to 2.5 A/cm2, the oxygen content of the deposited films decreases from 24 to 14 at.%, leading to a transition in microstructure from fully amorphous to mixed amorphous/nanocrystalline. In addition, the crystallization behavior and mechanical properties of the as-deposited amorphous Mo76O24 films were studied. The present work not only shows a novel method for producing amorphous alloy with a high refractory metal and oxygen content, but also verifies that oxygen could act as a main constituent in the formation of amorphous alloys.

Plain Language Summary Using in situ data, satellite observations, and model outputs, we analyzed the interannual variability in coastal upwelling intensity in the northern South China Sea. Comparing coastal upwelling observed from three cruises during the summers of 2008 and 2016, we found that coastal upwelling was stronger during 2016 compared to 2008, although the local upwelling favorable wind was stronger in 2008. The stronger near-bottom cross-shelf current and shallower thermocline in the slope resulted in stronger upwelling intensity during the summer of 2016. The topographic position index (TPI), which is defined by the sea surface temperature difference between one center cell and its neighbors, was used to quantify the interannual variability in upwelling. Stronger (weaker) upwelling intensity occurred during the summers of 2007, 2008, 2011, 2015, and 2016 (2004, 2009, 2012, and 2014) when the local wind was more favorable (less favorable) to coastal upwelling. The correlation coefficient between the area-weighted TPI and alongshore wind speed was -0.60, thereby confirming that local wind is the primary dynamical factor controlling the interannual variability in upwelling intensity. The correlation coefficient between the area-weighted TPI and the eastward boundary current transport averaged between the 75- and 100-m isobaths on the shelf was -0.42, indicating that the interannual variability in large-scale circulation in the northern South China Sea also contributes to the interannual variability in upwelling intensity. The anomalously shallow thermocline in the summer of 2016 was likely associated with the strong 2015-2016 El Nino event through planetary wave propagations.

Based on reanalysis data, we find that the Indian Ocean Dipole (IOD) plays an important role in the variability of wave climate in the equatorial Northern Indian Ocean (NIO). Significant wave height (SWH) in the equatorial NIO, especially over the waters southeast to Sri Lanka, exhibits strong interannual variations. SWH anomalies in the waters southeast to Sri Lanka correlate well with dipole mode index (DMI) during both summer and autumn. Negative SWH anomalies occur over the oceanic area southeast to Sri Lanka during positive IOD events and vary with different types of IOD. During positive prolonged (unseasonable) IOD, the SWH anomalies are the strongest in autumn (summer); while during positive normal IOD, the SWH anomalies are weak in both summer and autumn. Strong easterly wind anomalies over the southeast oceanic area of Sri Lanka during positive IOD events weaken the original equatorial westerly wind stress, which leads to the decrease in wind-sea waves. The longer wave period during positive IOD events further confirms less wind-sea waves. The SWH anomaly pattern during negative IOD events is nearly opposite to that during positive IOD events.

The South China Sea (SCS) and the Arabian Sea (AS) are both located roughly in the north tropical zone with a range of similar latitude (0°–24°N). Monsoon winds play similar roles in the upper oceanic circulations of the both seas. But the distinct patterns of chlorophyll a (Chl a) concentration are observed between the SCS and the AS. The Chl a concentration in the SCS is generally lower than that in the AS in summer (June–August); the summer Chl a concentration in the AS shows stronger interannual variation, compared with that in the SCS; Moderate resolution imaging spectroradiometer (MODIS)-derived data present higher atmospheric aerosol deposition and stronger wind speed in the AS. And it has also been found that good correlations exist between the index of the dust precipitation indicated by aerosol optical thickness (AOT) and the Chl a concentration, or between wind and Chl a concentration. These imply that the wind and the dust precipitation bring more nutrients into the AS from the sky, the sub-layer or coast regions, inducing higher Chl a concentration. The results indicate that the wind velocity and the dust precipitation can play important roles in the Chl a concentration for the AS and the SCS in summer. However aerosol impact is weak on the biological productivity in the west SCS and wind-induced upwelling is the main source.

The China–Sri Lanka Joint Center for Education and Research for the 21st Century Maritime Silk Road (CSL-CER) was established in August 2015. The Joint Center is an overseas science and education platform established by Chinese Academy of Sciences. CSL-CER has conducted a series of research activities, including an annual scientific expedition to the eastern Indian Ocean, with many kinds of instruments installed for monsoon and ocean observation. The ‘Numerical Forecast System for the Surrounding Area of Sri Lanka,’ which was developed by the Joint Center, can provide rapid mapping on multiple scales and at multiple resolutions for numerical forecast products serving local society. The annual China–Sri Lanka Joint Workshop on Monsoon Climate and Ocean Environment was successfully held in 2015 and 2016. According to the Memorandum of Understanding (MOU) on joint Master’s degrees, 15 new Master’s students were accepted by University of Chinese Academy of Sciences (UCAS) in 2015.

In the present work, the compatibility of additivity rule with the crystallization behavior of an Au 50 Cu 25.5 Ag 7.5 Si 17 glass forming alloy on the conditions of both isothermal and isochronal transformations is investigated. Taking advantages of the ultrafast heating and cooling rates of the Flash DSC technique, we verified the additivity rule in a solidification process for the first time. It is proved to be effective in predicting the beginning and the end of isochronal crystallizations during continuous heating and cooling from the kinetic analysis of corresponding experimental isothermal transformation. The predicted isochronal curves are fairly in accordance with the experimental results, especially for the incubation and crystallization processes during rapid solidification of the glass forming liquid. The compatibility of additivity rule enables a conversion between isothermal and isochronal transformations for the crystallization of supercooled liquid even during solidification from the melt.

The crystallization behavior of Au50Cu25.5Ag7.5Si17 metallic glass during continuous heating/cooling and isothermal treatment is investigated by ultrafast calorimetry. The relationship between the transformation and the time/temperature scales of the alloy is established experimentally in a wide temperature range from glass transition temperature to the melting point. Temperature-dependent viscosity in the expanded supercooled liquid region is derived from the thermodynamic and kinetic analysis of the crystallization behavior of the metallic glass. The nucleation rate and growth velocity for crystallization of the supercooled liquid are analyzed by applying classical nucleation theory and diffusion-controlled growth theory.

The summer monsoon onset over the South China Sea (SCS) is an abrupt event in May or early June every year. After the summer monsoon onset in 1998 and 1999, strong near-inertial oscillations (NIOs) in the central SCS were observed with Acoustic Doppler Current Profilers (ADCP) mooring data. The near-inertial current speed reached 0.25 ms−1, comparable to that induced by tropical storms (TS) in the same area, although the wind speed (~10 ms−1) of the monsoon onset was much lower than what is typical of TSs. Further analyses suggest that the shallow mixed-layer (

Using high-resolution in situ data from gliders, satellite data of sea level anomaly and geostrophic currents, we presented the detailed structure of an anticyclonic eddy during spring 2015 in the northern South China Sea. The impact depth of the anticyclonic eddy reached about 1000 m and had a maximum temperature anomaly of about 3°C at ∼120 m and maximum salinity anomaly of more than 0.3 psu in the mixed layer. The maximum geostrophic velocities perpendicular to the glider path were about 0.3 m s−1 at 100 m. The estimated radius was about 72 km and the translation velocity was about 5.2 cm s−1. The rotational speed of the eddy was estimated to be 0.35 m s−1. The high temperature and large salinity of the anticyclonic eddy indicated it did not originate from the South China Sea locally. The analysis of water mass indicated the character of the eddy water was similar to Kuroshio water, and the time evolution of the sea level anomaly and surface geostrophic velocity anomaly further validated that it originated from the Kuroshio intrusion as a loop current to the southwest of Taiwan.

We examine near-inertial variability of the meridional overturning circulation in the South China Sea (SCSMOC) using a global 1 / 12° ocean reanalysis. Based on wavelet analysis and power spectrum, we suggest that deep SCSMOC has a significant near-inertial band. The maximum amplitude of the near-inertial signal in the SCSMOC is nearly 4 Sv. The spatial structure of the signal features regularly alternating counterclockwise and clockwise overturning cells. It is also found that the near-inertial signal of SCSMOC mainly originates from the region near the Luzon Strait and propagates equatorward at a speed of 1–3 m s−1. Further analyses suggest that the near-inertial signal in the SCSMOC is triggered by high-frequency wind variability near the Luzon Strait, where geostrophic shear always exists due to Kuroshio intrusion.

Temperature (T) and salinity (S) profiles from conductivity-temperature-depth data collected during the Northern South China Sea Open Cruise from August 16 to September 13, 2008 are assimilated using Ensemble Kalman Filter (EnKF). An adaptive observational error strategy is used to prevent filter from diverging. In the meantime, aiming at the limited improvement in some sites caused by the T and S biases in the model, a T-S constraint scheme is adopted to improve the assimilation performance, where T and S are separately updated at these locations. Validation is performed by comparing assimilated outputs with independent in situ data (satellite remote sensing sea level anomaly (SLA), the OSCAR velocity product and shipboard ADCP). The results show that the new EnKF assimilation scheme can significantly reduce the root mean square error (RMSE) of oceanic T and S compared with the control run and traditional EnKF. The system can also improve the simulation of circulations and SLA.

Based on the global position system (GPS) radiosonde data near the sea surface, the surface duct characteristics over the South China Sea (SCS) were statistically analyzed. The annual surface duct occurrence over the SCS was about 64%. Of the observed surface ducts, duct heights mainly distributed between 18 and 42 m, with M slopes in the range of–0.3 to–0.2 M units/m. Those ducts accounted for about 80% of the ducting cases. For the total profiles, the duct occurrences in a day changed slowly and were more than 60% in all times. The surface ducts formed more easily in the daytime than in the nighttime and most of the duct height were at bellow about 32 m. Additionally, The seasonal variation of the SCS ducts appeared to be evident, except that the mean duct thickness was almost constant, about 33 m for all seasons. The highest occurrence was about 71% in the autumn, followed by in the summer, spring and winter. In spring, their top-height existed more often at a height of more than 48 m. Their mean duct strength became stronger trend from spring to winter, with the M-slope in the range between–0.26 and–0.18 M units/m. Those results agreed well with other studies, provided considering the data resolution. The statistical analysis was reliable and gave the duct estimation for the SCS. Such duct climatology not only has important implications for communication systems and the reliability of the radar observation, but also can provide useful information to improve the accuracy of the meteorological radar measurements.

A study of the Xisha eddy is a good supplement to comprehend the local oceanic and atmospheric currents. Our work aims at analyzing the intraseasonal Air–Sea interaction process during the occurring of the Xisha warm eddy. Using a Complex Empirical Orthogonal Function statistical technique, we found an eddy that propagated southwestward along the continental slope of the northwestern South China Sea, at a similar phase speed to that of Rossby waves, at 0.12 m s−1. Intraseasonal variability in spring is related to the ocean-to-atmosphere interaction, and involves the cloud-radiation effects on surface sea temperature, as well as its impact on lower-level convergence over the South China Sea. This process, induced by the warm eddy, results in abnormal surface sea temperature, downward shortwave/longwave radiation flux, surface latent heat flux, and wind changes. We used composite results and the Weather Research and Forecasting Model to explore how the observed surface sea temperature anomalies influence precipitation in the South China Sea. The results showed that the atmospheric transport of heat and moisture improved with respect to the surface sea temperature max and the air active events have caused lower atmosphere instability, along with the lower pressure and enhanced precipitation frequency in spring.

The variation of marine meteorology elements and the heat flux at Yongxing Island were investigated in September 2013 using observational data collected by the Yongxing Island Air–Sea Flux Tower. Heat flux was measured through eddy covariance and estimated using the bulk flux method. The traditional thirty-minute average method was employed to analyze the eddy covariance data. A TOGA–CORE 3.0 Algorithm was used to estimate the bulk flux. Capacity of the Advanced Weather Research and Forecasting model to simulate the variations in marine meteorological elements was evaluated using the observational data obtained during the same period. Observations suggested a response by the different parameters that were synchronous to the retreat of the monsoon around 7 September 2013. Surface air masses became cool and dry, and the downward short (long) wave radiation was reduced (increased). The Weather Research and Forecasting model simulated the variation of the atmospheric elements well, as observed by the Air-Sea Flux Tower in September 2013. The model was very accurate in simulating surface wind, radiation, and scalar–humidity. However, it failed to simulate the dramatic variations of surface air temperature, though it successfully reproduced the retreat of the summer monsoon, but weakened during the onset of the typhoon. The sensible flux simulated through the model was between the fluxes estimated through the bulk flux and eddy covariance flux. It also overestimated the latent heat flux at times, particularly after 20 September.

The observed characteristics of lower atmospheric ducts over the South China Sea (SCS) were analyzed based on Global Position Systerm (GPS) radiosonde data collected four times daily during autumn open cruises from 2006 to 2012. Duct occurrence, thickness, and strength over the SCS were about 40%, 150-m thick, and 8 M units, respectively, which were larger than during the summer monsoon period. Most ducts occurred at heights

Analyzing the observed currents at Xisha (110.3899 degrees E, 17.1038 degrees N) during May 2009 to May 2010, it is found that the kinetic energy has significant mesoscale variability, and each peak responds to large positive/negative ocean surface current curl caused by mesoscale eddies. Compared the kinetic energy with the wind stress work and the pressure work, it is also found that the barotropic pressure work which is mainly contributed by the sea surface height (SSH) corresponding to the mesoscale eddies behaves like the kinetic energy. The contribution of the mesoscale eddies to the kinetic energy can be up to 90% sometimes and reach deep level every time. Using the satellite altimeter data, the paths of mesoscale eddies contributing to the kinetic energy variability are traced back. In the winter half of the year, the mesoscale eddies propagating along the northern South China Sea shelf or across the basin from the west of the Philippines toward Xisha arrive at Xisha, influencing the kinetic energy. In the summer half of the year, the mesoscale eddies are mainly from the south, which were shed from the Vietnam coast current. And the cause for eddy shedding may be related to the relaxation of the Ekman transport anomalies.

Analyses of moored current meter data from the South China Sea (SCS) Coastal Oceanographic Process Experiment Pilot Project (SCOPE-PP) reveal that strong spatial variation in the vertical structure of coastal currents in the northern SCS (NSCS) was caused by the interaction between the Pearl River plume (PRP) and the alongshore coastal jet. Observations indicate that the NSCS coastal current was generally eastward, spreading the PRP water eastward. The lighter brackish plume residing on the top of the saline, coastal water strengthened the stratification near the surface and blocked the downward momentum transport, resulting in a strong vertical shear of the velocity at the mooring site S205. Meanwhile, the plume water raised the sea level. Because of the geostrophic balance in the across-shore direction, the eastward coastal current in the upper layer strengthened on the onshore side (near S205) and weakened on the offshore side (near S206 and S305) due to the plume water intrusion. Therefore, the vertical shear of the velocity was enhanced at S205 and reduced at S206 and S305. Moreover, because the plume varied substantially with the wind, the vertical shear of the velocity responding to the wind was different between S205 and S206. The numerical simulation during summer 2008 confirms that the PRP enhances (weakens) the vertical shear of the velocity on the onshore (offshore) side by increasing (decreasing) the upper-layer current by about 0.2 m s-1 and decreasing (increasing) the middle-layer current slightly.

The pattern of meridional overturning circulation (MOC) in the South China Sea (SCS) is studied using a numerical Lagrangian tracing method with the HYCOM+NCODA Global 1/12 degrees Analysis (GLBa0.08) data. The SCS MOC has a sandwich structure, which consists of a layer of stronger clockwise circulation above 500 m depth, a counterclockwise layer in the mid layer between 500 and 1000 m depth, and a weaker clockwise layer below 1000 m. The deep (below 1000 m depth) clockwise layer is divided into three cells, namely, the deep southern MOC cell, DSMOC; the deep middle MOC cell, DMMOC; and the unclosed deep northern MOC cell, DNMOC. The inflow through the Luzon Strait is the main source for the SCS MOCs. The upper layer Luzon Strait inflow dominates the upper SCS MOC structure but has relatively less contribution to the DNMOC, whereas the deep layer Luzon Strait inflow mainly influences the DNMOC and it mostly rises near 18 degrees N. The inflow through the Taiwan Strait mainly contributes to the upper layer MOC. Moreover, inflows from the Mindoro and Karimata straits contribute negatively to the upper MOC but play a significant role on the DSMOC. The backward integration of Lagrangian trajectories further validates that the SCS deep water comes not only from the deep inflow but also from the entrainment of the middle and upper layer inflow through the Luzon Strait. In the SCS basin, there are three northwest-southeast tilted zones where tracers upwell, which correspond to the three deep MOC cells. One possible mechanism for these upwelling zones is the interaction between the continental slope-trapped waves and the westward planetary Rossby waves.

Using surface and aerological meteorological observations obtained at the Xisha Automatic Weather Station and three moored buoys along the continental slope, characteristics of the synoptic-scale disturbances over the northern South China Sea (NSCS) are extensively studied. The power spectra of surface and aerological observations suggest a synoptic feature with a pronounced energy peak at a period of 5–8 d and a weak peak at 3–4 d. The standard deviation of the synoptic temperature component derived at Xisha Station from 1976 to 2011 indicates that the strongest variability normally exists in August all through the whole troposphere. At the interannual scale, it is found that El Nino plays an important role in regulating the synoptic disturbances of atmosphere. The vertical synoptic disturbances have a double active peak following El Nino condition. The first peak usually occurs during the mature phase of El Nino, and the second one occurs in the summer of decay year. Comparing with the summer of developing years, the summer of the decaying year of El Nino has more active and stronger synoptic disturbances, especially for the 5–8 d period variations.

The major goal of this study was to find match-ups between thermal fronts mapped from satellite sea surface temperature SST imagery and from in situ data in the southern South China Sea SSCS, using 11 ship surveys conducted by the South China Sea Institute of Oceanology SCSIO between 1987 and 1999. Fronts were automatically detected by the Cayula–Cornillon multi-image edge detection algorithm CCA applied to satellite-derived maps of the Advanced Very High Resolution Radiometer AVHRR SST obtained from the Pathfinder project 8364 twice-daily global fields with 9 km resolution between 1985 and 1996. Twice-daily near-instant frontal maps were composited without any averaging or smoothing to produce individual monthly frontal maps covering the period from January 1985 through December 1996 144 maps in total. Although the SSCS is a tropical sea with little SST difference between water masses, the CCA turned out to be an effective tool for front mapping in the SSCS. Out of the 11 ship surveys analysed in this study, four surveys produced satisfactory match-ups. The percentage of match-ups is considered reasonably high given that 1 ship surveys were not optimized to cross fronts, therefore most in situ sections missed fronts; 2 satellite measurements of SST with AVHRR are hampered by cloudiness, therefore satellite-derived frontal maps might miss some fronts masked by persistent cloudiness. Fronts are more distinct in winter, when cross-frontal SST gradients are enhanced. From oceanographic vertical sections and horizontal maps, fronts are much sharper in the subsurface layer represented here by 50 m level. Nonetheless, the CCA successfully detected SST fronts with a cross-frontal step as small as 1°C.