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Ocean currents in the southern East China Sea (ECS) are complex and have long lacked systematic observational data. Observations from coastal radars in northern Taiwan, along with several drifters and satellite data, reveal a detailed ECS surface flow structure and thermal front. Drifter trajectories followed the seasonal flow field and were oscillatory and trapped due to strong tidal currents. Three drifters crossed the oceanic front off the northern coast of Taiwan following the tidal motion with a rapid change in the sea surface temperature by 2.5°C, which was recorded within a small distance of 500 m. A significant seasonal water mass exchange cycle occurred in the southern ECS. Starting in October, the Kuroshio Current intrudes onto the ECS shelf, causing the formation of a southwestward Northern Taiwan Coastal Current that mixes with the China Coastal Current to form a southward flow in the northern Taiwan Strait. Beginning in March, the ocean current off northwestern Taiwan shifts northward and then gradually flows eastward into the Kuroshio region. With satellite‐derived and model‐simulated surface currents contradicting each other over long periods of time, hourly coastal radar data have not only successfully explained the spatiotemporal variations in the sea surface temperature, salinity, and chlorophyll concentration observed by satellites but have also resolved the long‐standing disputes over the surface currents in the southern ECS. Plain Language Summary: In the southern East China Sea (ECS), the ocean surface currents observed by satellite altimeters and estimated based on numerical models have considerably differed for a long time, especially in winter. The data observed by shore‐based high‐frequency radar have yielded new discoveries. Beginning in October, the Kuroshio Current intrudes onto the ECS shelf and pushes Kuroshio waters with high temperatures, high salinities, and low chlorophyll concentrations to the west, causing the current from northern Taiwan to flow southwestward into the Taiwan Strait (TS). Then, starting in March, ocean currents off northwestern Taiwan turn northward, and the water off northern Taiwan is pushed eastward back to the Kuroshio region. These flow field variations cause a significant oceanic front in the 121°E−122°E area in the southern ECS. We deployed four surface velocity program (SVP) drifters to observe the ocean flow and used virtual drifters to simulate the distribution probability of the track in each month. The drifters basically followed the movement direction of the seasonal flow field but could have been affected by the significant tidal currents and become trapped. With this study, we aim to better understand the southern ECS environment from a geophysical perspective. Key Points: Coastal radar data and long‐term multisatellite data are used to observe the formation of oceanic fronts driven by ocean currentsThe Kuroshio Current's intrusion of the shelf causes the Northern Taiwan Coastal Current to flow southward along western Taiwan in winterVirtual drifter experiments present the possible trajectories of and seasonal changes in near‐surface ocean currents [ABSTRACT FROM AUTHOR]

Recent satellite sea surface height (SSH) and sea surface temperature (SST) observations have shown that abnormal eddies, that is, warm cyclonic eddies and cold anticyclonic eddies occur sporadically in some regions, which triggers an essential question on the spatiotemporal distribution of abnormal eddies in the global ocean. In this study, a deep learning framework was developed to systematically mine information from the synergy of satellite‐sensed global SSH and SST data over the 1996–2015, 20‐year period. Abnormal eddies account for a surprising one‐third of total eddies and are active along the Equatorial Current and high unstable currents. Normal (abnormal) eddies are stronger in winter (summer) in the North Hemisphere and vice versa in the Southern Hemisphere. The annual mean amplitudes of normal eddies are larger than that of abnormal eddies. Crucially, the daily number of normal (abnormal) eddies increased (decreased) 9.68 (11.80) every year. Plain Language Summary: Mesoscale eddies are broadly distributed in the global ocean and play a significant role in transporting energy, heat, and mass. This study is the first to demonstrate characteristics of both normal eddies (cold cyclonic eddies and warm anticyclonic eddies) and abnormal eddies (warm cyclonic eddies and cold anticyclonic eddies) in the global ocean. The study developed a deep learning‐based model to detect normal and abnormal eddies from the synergy of 20‐year satellite‐derived global sea surface height and sea surface temperature observations. Abnormal eddies account for a surprising one‐third of total eddies in the global ocean. Besides, the increase of normal eddies' number and the decrease of abnormal eddies' number are proposed to be related with the long‐term variation trend of ocean currents in the global ocean. Key Points: Abnormal eddies (warm cyclonic eddies and cold anticyclonic eddies) account for a surprising one‐third of total eddies in the global oceanThe spatiotemporal variabilities of abnormal eddies are significantly different from those of normal eddies in the global oceanThe daily number of normal (abnormal) eddies has an increasing (decreasing) trend during 1996–2015 [ABSTRACT FROM AUTHOR]

Tidal current‐induced cyclonic eddies cause cold‐water upwelling and periodic sea surface temperature (SST) drops around the coral reef area in Nanwan Bay, which is located at the southern tip of Taiwan. This study used Himawari‐8 satellite data and tide gauge and coastal ocean dynamics application radar (CODAR) data to analyze the characteristics of the SST drops and cyclonic eddy propagation and used an oceanic general circulation model (OGCM) to simulate the tidal current flowing process. According to the CODAR data analysis, the mixed primary semidiurnal tide had an average current velocity of 0.3–0.4 m s−1 throughout the bay, and the average life cycle of a cyclonic eddy is 6.6 hr, with a propagation speed of 0.35 m s−1. The SST drop during the spring tide period was greater than that during the neap tide period, and the SST dropped in both summer and winter. The average daily SST drop in the summer reached 2 °C with a maximum observed value of 4.7 °C, and the SST drop rate was 0.3–0.5 °C hr−1. The annual mean chlorophyll‐a concentration was 0.25 mg m−3. This study explored the special properties of the Nanwan Bay coral reef area from the perspective of ocean physics to allow ecologists to facilitate the implementation of long‐term conservation and monitoring programs. Plain Language Summary: In recent years, the increased global sea temperatures have caused severe coral bleaching; however, Nanwan Bay has suffered a comparatively smaller impact. To understand why, we analyzed satellite and radar data. We found that Nanwan Bay experienced an almost daily sea surface temperature (SST) drop during the summer and that this periodic variation was caused by a cyclonic eddy upwelling cold water to the surface. In the summer, the SST drop was 2 °C on average and dropped at a rate of 0.3–0.5 °C hr−1. The observational record indicated that the water cooled as much as 4.7 °C in 1 day. These eddies were caused by the unique topography in this area of the bay; they survived an average of 6.6 hr and moved at a rate of 0.35 m s−1. The formed eddies disappeared in the bay or flowed southward out of the bay. With this study, we hope to help marine ecologists understand the Nanwan Bay environment from a geophysical perspective so that they have sufficient background knowledge when investigating coral biology and coral reef ecology in the future. Key Points: Himawari‐8 satellite and coastal radar data are used to analyze the characteristics of eddy‐induced sea surface temperature drop in a bayIn summer, ebb current‐induced cyclonic eddies cause 2 °C sea surface temperature drops that reduce thermal stressThe average life cycle of eddies was 6.6 hr with propagation speed of 0.35 m s−1, which was close to the tidal currents around the bay [ABSTRACT FROM AUTHOR]

In this study, we for the first time observed two subsurface cyclonic eddies (SCEs) in the southeastern Tropical Indian Ocean. One SCE (SCE‐C) was observed along 8°S transect during the cruise conducted in July 2016. Another SCE (SCE‐A) was also observed near 8°S but by an Argo float in November 2005. The SCE‐C had a maximum thickness of about 500 m (300–800 m) and a radius of ~90 km, while the SCE‐A has a vertical extent of 700 m (200–900 m) and a radius larger than 110 km. The water trapped by SCE shows a three‐compartment structure. Both the two SCEs are characterized by stratified water with negative lens structure and cause prominent temperature/salinity/spiciness anomalies in a wide density range. As the water carried by SCEs is stratified, we can trace the SCE origin by finding an area sharing the same water property with the SCE on different density surfaces. The result suggests that the two SCEs originate from the southwest coast of the Sumatra Island. Considering the topography and hydrologic characteristics of the SCE origin, we speculate that the SCEs are generated due to topography‐induced South Java Undercurrent instability. Plain Language Summary: Subsurface eddies usually have long lifespans and can carry fluid parcels and transport them far away from the eddy origin. However, compared with surface eddies, subsurface eddies are poorly observed because they usually have small or no surface signatures. In this study, we for the first time observed two subsurface cyclonic eddies (SCEs) in the southeastern tropical Indian Ocean. The SCEs were characterized by stratified water with negative lens structure. Further analysis suggested that the SCEs should be generated off southwest coast of the Sumatra Island due to topography‐induced South Java Undercurrent instability and move southwestward. These results provide new insight into the SCEs in the southeastern tropical Indian Ocean. Key Points: Two subsurface cyclonic eddies are observed in the southeastern Tropical Indian OceanThe subsurface cyclonic eddies are characterized by stratified water and cause prominent water property anomalies in a wide density rangeThe subsurface cyclonic eddies should be generated off southwest coast of the Sumatra due to topography‐induced undercurrent instability [ABSTRACT FROM AUTHOR]

Field observations were conducted along three west‐east transects in the East China Sea Kuroshio Front in July 2017. The microstructure observations results show that the surface turbulence kinetic energy (TKE) dissipation rates in the northern and southern transects are about 2 orders larger than those in the middle transect. The sea surface temperature, mixed layer depth, and the submesoscale motions (with horizontal scales smaller than 30 km) also suggest the surface turbulences are more active in the northern and southern transects. The current velocity data and sea level anomaly show that the middle transect was located at the northern edge of a cyclonic eddy. The eddy‐generated cross‐front geostrophic current was observed to flow toward the opposite direction of the cross‐front Ekman transport and believed to counteract the Ekman buoyancy flux (EBF)‐induced turbulence enhancement. The TKE dissipation rates can be well scaled by a scaling considering the EBF and the wind in the northern and southern transects but wind scaling only in the middle transect, suggesting the EBF does not contribute to the surface turbulence in the middle transect. An improved empirical scaling considering the cross‐front geostrophic current is defined and can scale the TKE dissipation rates better, indicating an eddy plays a key role in surface turbulent mixing in the East China Sea Kuroshio front. Plain Language Summary: Ocean surface boundary layer is an important mediator for air‐sea interaction. Recent field observations have shown that the turbulence mixing within the ocean surface boundary layer can be significantly elevated at the front when the cross‐front Ekman transport carries dense cold water over less dense warm water. Our observations show that the mesoscale eddy also plays an important role in the surface turbulence at the front by generating cross‐front geostrophic current. This result may have important implications on the ocean model and climate forecast. Key Points: Expected Ekman buoyancy flux‐induced surface turbulence enhancement was not observed in the Kuroshio FrontEddy‐generated cross‐front geostrophic current counteracted the Ekman buoyancy flux‐induced surface turbulence enhancementNewly defined empirical scaling considering geostrophic current can better scale observed turbulent dissipation rates [ABSTRACT FROM AUTHOR]

Multi-sensor data from different satellites were analysed to study the interannual variability of the cold domes northeast of Taiwan. From the empirical orthogonal function analysis of along-track satellite altimeter data and sea surface temperature, both revealed a cold dome phenomenon located at approximately 122°36´E and 25°24´N, and their principal components demonstrated a variation of 4-6 years. The cold dome variation correlates best with the Oceanic Niño index and poorly with Pacific Decadal Oscillation index. The forcing could be wind stress curl and Kuroshio volume transport, which produce an upwelling around the Men-Hua Canyon. Positive wind stress curl and the on-shelf water transport of the Kuroshio Current through the North Men-Hua Canyon increase the chance of the cold dome formation which may be responsible for the interannual variability of cold domes. [ABSTRACT FROM AUTHOR]

The intraseasonal variability of the winter western boundary current (WBC) in the South China Sea (SCS) is investigated using satellite data and mooring observations. The intraseasonal intensification of the northeasterly wind enhances the cross-shelf sea-level gradient, and, thus, causes the basin-scale cyclonic circulation to spin up within around one week. The Southern Cyclonic Gyre in the southwestern SCS further strengthens due to the intensified inertial recirculation of the WBC. Complex empirical orthogonal function analysis reveals that the large sea-level fluctuation around the downstream WBC can mainly be explained by two dominant modes. The first mode is related to intraseasonal variations of the wind field and its spatial field represents the response of the WBC to the westward Rossby waves originated from the interior basin, while the second mode reflects the southward propagation of mesoscale signals along the WBC. Mooring observations recorded the accelerations of the southward WBC three times in winter 2004/2005. While the first two could be linked to the wind intensification, the third one was associated with a cyclonic eddy closely next to the WBC. Initially, this eddy propagated from the Luzon Strait, where active mesoscale processes associated with the Kuroshio intrusion act as important disturbance sources for the SCS. [ABSTRACT FROM PUBLISHER]

Using cruise observations and reanalysis data, this study analyzes the effects of wind, freshwater, and turbulent mixing on the two upwellings: one is off the eastern coast of Hainan Island (HEU) and the other is off the northeastern coast of Hainan Island (HNEU). During the cruise in 2009, the HNEU occurred with southwesterly to southeasterly wind. The relative large values of turbulent kinetic energy dissipation rate and diffusivity estimated from the Thorpe scale indicate that the upwelling water is further uplifted to the surface by strong turbulent mixing in the HNEU region. But the HEU was not observed under the southeasterly wind. During the cruise in 2012, the HNEU disappeared in the upper layer with freshwater covered and southeasterly wind, while the apparent HEU only accompanied with southwesterly wind. To obtain the general characteristics, we define three types of upwelling patterns, i.e., the intensified HEU, the intensified HNEU, and both HEU and HNEU in one day, using the reanalysis data. The composites of sea surface temperature (SST), wind, and precipitate for each upwelling pattern identify that the HNEU is associated with the prevailing southeasterly wind and can be limited in the lower layer when it is covered by freshwater. But the HEU is mainly driven by southwesterly wind but is not remarkably affected by freshwater. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) data derived from satellite and in situ measurements are used to study the thermal variability in the South China Sea (SCS). Time-frequency-energy distributions, periods of variability, and trends are computed by the Hilbert-Huang transform method. The SST trend from 1982 to 2005 is 0.276°C per decade in the SCS which is higher than 0.144°C per decade in the western Pacific warm pool (WPWP). The warm pool (SST ≥ 28°C) area in the SCS has increased by 0.20 × 10 km per decade. The SST and area of the warm pool in the SCS are strongly correlated, respectively, with the SST and area of the WPWP with a time lag of 1 month, suggestive of a strong connection between these two warm pools. Once the annual cycle is eliminated, decadal oscillations dominate the variability of SST and warm pool area in the SCS. [ABSTRACT FROM AUTHOR]

An objective classification method is developed to distinguish the water masses of Kuroshio and South China Sea (SCS) by using an artificial neural network (ANN). Sea surface temperature (SST) and ocean-color data obtained from the Moderate Resolution Imaging Spectroradiometer in two specified areas to the east and west of Luzon, representing the Kuroshio and SCS waters, respectively, are used to train, validate, and test the ANN model. The water masses of Kuroshio and SCS can be distinguished correctly with a high success rate of over 99%. The model is then applied to the Luzon Strait, and the result of water mass classification agrees well with the temperature-salinity characteristics derived from a cruise in May and June of 2006. The performance is good in summertime when the SST or ocean color has a rather uniform spatial distribution and the traditional method of front detection by using a threshold value is inappropriate. [ABSTRACT FROM PUBLISHER]

The Kuroshio Current has its origin in the northwestern Pacific, flowing northward to the east of Taiwan and the northern part of Luzon Island. As the Kuroshio Current flows northward, it quasi-periodically intrudes (hereafter referred to as Kuroshio intrusion (KI)) into the northern South China Sea (SCS) basin through the Luzon Strait. Despite the complex generation mechanisms of KI, the purpose of this study is to improve our understanding of the effects of KI through the Luzon Strait on the regional atmospheric and weather variations. Long-term multiple satellite observations, including absolute dynamic topography, absolute geostrophic currents, sea surface winds by ASCAT, multi-scale ultra-high resolution sea surface temperature (MURSST) level-four analysis, and research-quality three-hourly TRMM multi-satellite precipitation analysis (TMPA), was used to systematically examine the aforementioned scientific problem. Analysis indicates that the KI is interlinked with the consequential anomalous precipitation off southwestern Taiwan. This anomalous precipitation would lead to ~560 million tons of freshwater influx during each KI event. Subsequently, independent moisture budget analysis suggests that moisture, mainly from vertical advection, is the possible source of the precipitation anomaly. Additionally, a bulk formula analysis was applied to understand how KI can trigger the precipitation anomaly through vertical advection of moisture without causing an evident change in the low-level flows. These new research findings might reconcile the divisiveness on why winds are not showing a synchronous response during the KI and consequential anomalous precipitation events. [ABSTRACT FROM AUTHOR]

The spatial and temporal variability of the Kuroshio surface axis northeast of Taiwan Island is investigated using 24 years of surface geostrophic currents derived from satellite altimeter data from 1993 to 2016. The Kuroshio surface axis is derived by an extraction method with three selected parameters, including the length of the subsidiary line, the intervals between two adjacent points, and the distance between the two adjacent subsidiary lines. The empirical mode decomposition analysis on the 24-year Kuroshio axes reveals that the mean periods of intra-seasonal and inter-annual variability, which are the two dominant components, are about 3.2 months and 1.3 years, respectively. The self-organizing map analysis reveals that the variation of Kuroshio axis northeast of Taiwan Island has four best matching unit (BMU) patterns: straight-path (BMUS), meandering-path (BMUM) and two transition stages (BMUT1 and BMUT2). The straight-path pattern shows strong seasonality: more likely occurring in summer. The meandering-path pattern is less frequent than straight-path pattern. During a typical period from November 26, 2012 to January 27, 2013, which is chosen as an independent example, the analysis on the satellite altimeter and sea surface temperature data shows that the patterns of the Kuroshio axis change successively in order of BMUT1→BMUM→BMUT2→BMUS, i.e., the Kuroshio axis migrates from the meandering-path to the straight-path pattern. During the typical period the warm water intrusion and a mesoscale eddy occur at the second stage corresponding to BMUM and migrate northwestward gradually at the last two stages corresponding to BMUT2 and BMUS. The transient order appears only during this typical period but it is not common for the whole study period. The monthly mean relatively vorticity is calculated and analyzed to evaluate the impact of the eddies on the Kuroshio surface axis variability, the results show that the anticyclonic (cyclonic) eddies can promote the Kuroshio surface axis to present the meandering-path (straight-path) pattern because of the potential vorticity conservation. The impacts of the anticyclonic eddies and the cyclonic eddies on the variability of the Kuroshio surface axis are opposite. The long-term day-to-day detection contributes to improving understanding the variability of Kuroshio surface axis northeast of Taiwan Island. [ABSTRACT FROM AUTHOR]

Chlorophyll- a (Chl- a) is an essential ecological indicator, and affected by processes such as typhoons, mesoscale eddies, and Rossby waves. However, the impact of more frequent and widespread precipitation events on Chl- a seems to be overlooked. This study utilized remote sensing data and reanalysis data to investigate the response of Chl- a to 240 precipitation events in the central South China Sea from 2005 to 2019. The results indicate that precipitation events have a significant impact on Chl- a concentration. Following a precipitation event in 2019, the Chl- a concentration in the affected area increased by approximately 0.22 mg m−³ from the 3rd to the 7th day. The reasons for the increase in Chl- a concentration were the vertical mixing induced by wind stirring and the upwelling caused by wind stress curl, which transported nutrients to the euphotic zone, lowering the sea surface temperature and triggering a proliferation of phytoplankton. Additionally, dissolved nutrients in precipitation provided a nutrient source for Chl- a growth. The contributions of nutrient supply, wind speed, and wind stress curl to the increase in Chl- a concentration during precipitation events were 18%, 37%, and 45%, respectively. Precipitation events enhanced marine primary productivity, playing a crucial role in deepening our understanding of ocean-atmosphere interactions and their impact on marine ecosystem. • Higher chlorophyll-a concentration blooms are observed in summer and winter in the South China Sea. • The contributions of precipitation, wind speed, and wind stress curl to the increment of chlorophyll-a concentration are 18%, 37%, and 45%, respectively. • The strongest chlorophyll-a response after winter rainfall events occurs in 2013 and 2019. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we use multi-satellite remote sensing data and Regional Ocean Model System (ROMS) to examine the physical and biological responses to Typhoon Nakri during a period from 1 to 8 June 2008 in the western North Pacific. From satellite observations, we find remarkable surface cooling (∼5°C) and distinct phytoplankton enhancement after Nakri passage. It is interesting to note that in contrast to the well-documented rightward bias of the surface cooling response, the maximum biological response to Nakri occurred on the left of the Nakri’s track rather than the right side, where the most distinct cooling response occurred. To reveal the dynamic mechanism for this unusual phenomenon, we have done numerical experiments with and without the influence of preexisting cyclonic circulation and previous typhoon. The results from simulations show that both the physical and biological responses to Nakri are greatly affected by the preexisting cyclonic circulations. The discrepancy between the locations of maximum physical and biological responses mainly results from the advanced uplift and current advection of nutrient fields by previous typhoon Rammasun, which passed through the area about two weeks before Nakri. [Copyright &y& Elsevier]

Typhoon Fungwong, a category-2 but deadly typhoon in the 2008 Pacific typhoon season, made landfall first on Taiwan and then on Southeast China. During its approach toward Taiwan, it triggered an extreme sea surface temperature (SST) drop of 12.5 °C, which was the strongest SST drop recorded by Longdong buoy northeast of Taiwan coast from 1998 to 2017. In this study, including moored buoy temperature measurements, Argo float temperature profiles, satellite-observed SSTs, and a suite of numerical experiments performed using the Regional Ocean Modeling System were used to unveil the detailed processes of how Fungwong triggered such an extreme cooling. Subsequently, the source of the cold waters feeding the extreme cooling, possible mechanisms triggering the cooling, and consequential effects of cooling on the ambient ocean environment were systematically investigated. Results show that the extreme cooling was triggered mainly by a process of uplift of subsurface cold water tied to shore-ward Kuroshio intrusion driven by easterly/northeasterly winds and consequential entrainment mixing, while coastal upwelling driven by persistent longshore (southerly) winds plays a minor role. Nevertheless, the southerly winds still help the enhancement of entrainment mixing and thus the sea surface cooling. Finally, modeled float trajectories with temperature tracers identified where the cold water goes and indicate that the temperature drop might extend all the way toward the south end of Japan (Kyushu) along the flowing path of Kuroshio. • Typhoon Fungwong (2008) triggers an extreme sea surface cooling of 12.5 °C. • It is one of the strongest cooling responses ever recorded by in-situ instruments. • How Fungwong triggers such an extreme cooling was systematically resolved. • Combined effect of Kuroshio intrusion and enhanced entrainment triggers it. • Newly formed cold water impacts oceanic environment along Kuroshio downstream. [ABSTRACT FROM AUTHOR]

The Yellow and Bohai Seas (YBS) are shallow marginal seas located at the temperate latitudes of the western North Pacific. The seasonal bottom water temperature variation in the YBS can be greater than 20 °C and therefore generates significant seafloor heat flux, which significantly changes both the sediment temperature profile and heat content of the overlying water column. In this study, we investigated the seafloor heat flux driven by bottom water temperature variation in the YBS using a high-resolution numerical ocean model and a one-dimensional sediment temperature model. The results showed that seafloor heat flux in the area shallower than 50 m was on the order of 10 W/m2. The seafloor heat flux was larger than the lateral heat flux driven by circulation and ranked second only to surface net heat flux accounting for the most important forcing mechanism of ocean heat content variation in the coastal YBS. The accumulated seafloor heat flux during the sediment cooling/warming season could warm/cool the overlying water column by about 1 °C in the coastal YBS where the depth is shallower than 30 m. The depth of sediment affected by seafloor heat flux (seasonal sediment temperature variation >0.1 °C) could be as deep as 10 m. The complex spatial–temporal distribution of seafloor heat flux generated a complex distribution of sediment temperature and sound speed, which may have an important effect on acoustic wave propagation in the YBS. • Bottom water temperature variation generates significant seafloor heat flux. • Seafloor heat flux is on the order of 10 W/m2 in the coastal Yellow and Bohai Seas. • Seafloor heat flux affects ocean heat content significantly. • Seafloor heat flux generates complex sediment sound speed distribution. [ABSTRACT FROM AUTHOR]

This study analyzes the monthly variability of thermocline in the South China Sea (SCS) and the response of thermocline depth (TD) to ENSO events. The study is based on 51-year (1960-2010) monthly seawater temperature and surface wind stress data from Simple Ocean Data Assimilation (SODA), together with heat flux, precipitation and evaporation data from the National Centers for Environmental Prediction (NCEP), the National Oceanic and Atmospheric Administration (NOAA) and the Woods Hole Oceanographic Institution, respectively. The results reveal that the upper boundary depth, lower boundary depth, thickness and intensity of thermocline in the SCS show remarkable monthly variability. Being averaged for the deep basin of SCS (deeper than 200 m), the upper boundary depth deepens gradually from May to the following January and then shoals from February to May, while the lower boundary depth varies little throughout the whole year. Further diagnostics indicates that the monthly variability of the upper boundary depth is mainly caused by the buoyancy flux and wind stress curl. It is also indicated that the response of the SCS TD to the El Niño or La Niña events is in opposite phase. On one hand, the spatial-averaged TDs in the SCS appear as negative and positive anomalies during the mature phase of the El Niño and La Niña events, respectively. On the other hand, from June of the El Niño year to the subsequent April, the spatial patterns of TD in the north and south of 12°N appear as negative and positive anomalies, respectively, but present positive and negative anomalies for the La Niña case. However, positive and negative TD anomalies occur almost in the entire SCS in May of the subsequent year of the El Niño and La Niña events, respectively. [ABSTRACT FROM AUTHOR]