Search

An interdecadal change in the air-sea interaction over the South China Sea (SCS) after the late 1990s has been identified using a local contemporaneous precipitation-sea surface temperature (SST) and precipitation-SST tendency relationship. During 1979-1998, there is a negative precipitation-SST relationship over the SCS, with a larger magnitude over the northeastern SCS (NESCS) than over the southwestern SCS (SWSCS). The remote effect of warmer SST over the tropical Indian Ocean plays a crucial role in a strong anticyclone and suppressed rainfall over the SCS and western North Pacific. Due to greater mixed-layer depth over the SWSCS than over the NESCS, entrainment heat flux makes a larger contribution to a positive precipitation-SST tendency over the SWSCS than over the NESCS. The cloud-radiation effect has a dominant and positive contribution to the SST tendency over the NESCS, whereas it has a negative contribution to SST tendency over the SWSCS. In contrast, the precipitation-SST correlation becomes weakly negative over the NESCS and significantly positive over the SWSCS during 1999-2013. The CESM-CAM5 model demonstrates that cooler SST over the tropical central-eastern Pacific (TCEP) triggers a weak anticyclone, slightly suppressing rainfall over the SCS. The cloud-radiation effect still contributes mostly to a positive SST tendency over the NESCS. Warmer SST over the SWSCS induces an increase in surface evaporation and low-level moisture convergence and causes enhanced rainfall. That offsets the remote effect of TCEP SST and results in a negative precipitation-SST tendency with negative cloud-radiation feedback. The interdecadal change in remote forcing to SCS rainfall around the late 1990s is related to the evolution of TCEP SST anomalies from the preceding winter to summer, which is possibly modulated by the phase of the Pacific Decadal Oscillation. [ABSTRACT FROM AUTHOR]

Conductivity-temperature-depth observations, objectively analyzed data, and model output are used to investigate the variability of subsurface temperature in the South China Sea (SCS) during 1948-2010. Two extreme subsurface warm events are identified during 1998/99 and 2006/07, with no corresponding extreme surface warming except in 1998. Mixed-layer heat budget analysis reveals that the lack of significant heat input from surface net heat flux or from current advection is responsible for the absence of extreme surface warming during 1999, and 2006/07. The surface net heat flux alone cannot explain the first phases of subsurface warming during 1998/99 and 2006/07. Warm advection from the southern SCS in 1998/99 and from the Kuroshio intrusion in 2006/07, induced by anomalous ocean currents, is likely the major contributor to warming of the subsurface water. During the second phase of warming, the surface net heat flux plays a damping role to cool the subsurface water, and the warm advection induced by anomalous SCS western boundary currents from the southern SCS leads to extremely warm subsurface water anomalies. The results show the importance of the Pacific western boundary currents, especially the Kuroshio, in maintaining extreme subsurface warm events in the SCS. [ABSTRACT FROM AUTHOR]

We examined regional empirical equations for estimating the surface concentration of particulate organic carbon (POC) in the South China Sea. These algorithms are based on the direct relationships between POC and the blue-to-green band ratios of spectral remotely sensed reflectance, R ( λ)/ R(555). The best error statistics among the considered formulas were produced using the power function POC (mg/m)=262.173 [ R(443)/ R(555)]. This formula resulted in a small mean bias of approximately −2.52%, a normalized root mean square error of 31.1%, and a determination coefficient of 0.91. This regional empirical equation is different to the results of similar studies in other oceanic regions. Our validation results suggest that our regional empirical formula performs better than the global algorithm, in the South China Sea. The feasibility of this band ratio algorithm is primarily due to the relationship between POC and the green-toblue ratio of the particle absorption coefficient. Colored dissolved organic matter can be an important source of noise in the band ratio formula. Finally, we applied the empirical algorithm to investigate POC changes in the southwest of Luzon Strait. [ABSTRACT FROM AUTHOR]

This study investigates the interdecadal changes in summertime tropical cyclone (TC) frequency over the South China Sea (SCS) during 1979-2010. Based on changepoint detection algorithms and spectral analysis, two inactive TC periods (period 1: 1979-93 and period 3: 2003-10) and one active TC period (period 2: 1994-2002) have been identified, with a dominant spectral peak of approximately 9-10 yr. Correlation analysis further reveals a significant negative relationship between TC frequency and the zonal sea surface temperature gradient (ZSG) between the northern Indian Ocean (NIO) and the western North Pacific (WNP) at both interannual and interdecadal time scales. That is, a positive ZSG between the NIO and the WNP tends to suppress cyclogenesis over the SCS, whereas a negative ZSG is generally favorable for SCS TC formation. The negative connection between cyclogenesis and ZSG may be explained by the influences of the ZSG on atmospheric circulations as well as Madden-Julian oscillation (MJO) activity over the SCS, which reveal prominent contrasts during the study periods. A positive ZSG between the tropical Pacific and the Indian Ocean induces an anomalous Walker-like circulation, which results in an anomalous subsidence and boundary layer divergence over the northern SCS. This also suppresses the moisture as well as MJO activity over the SCS, leading to a significant reduction in TC frequency during inactive periods 1 and 3. In contrast, a negative ZSG induces surface westerlies and favorable environmental conditions for TCs, thereby greatly enhancing SCS cyclogenesis during period 2. [ABSTRACT FROM AUTHOR]

This study examines the impact of the cold tongue (CT) El Niño and the warm pool (WP) El Niño on tropical cyclone (TC) genesis over the South China Sea (SCS) from 1965 to 2010. During Sept-Oct-Nov (SON), the TC genesis exhibits clear interannual variability. SON TC genesis is significantly related with the WP Niño index, but not with the CT Niño index. It is found that in the past two decades the SCS TC genesis varies coherently with the WP Niño index on a timescale of approximately 4 years, which is in accordance with the recent increase in WP El Niño events. The distinctly different atmospheric teleconnection patterns related to the CT and WP El Niño over the SCS are responsible for these relationships. CT El Niño can induce anticyclone anomalies over the SCS and the western tropical Pacific WP. However, WP El Niño can result in dipolar patterns with anticyclone anomalies over the SCS and cyclone anomalies over the western tropical Pacific WP at low- and mid-level. These WP El Niño-related large-scale circulation anomalies enlarge the low-level northerlies over the SCS. This in turn enhances the vertical wind shear and thus suppresses TC genesis over the SCS. [ABSTRACT FROM AUTHOR]

We propose a bio-optical inversion model that retrieves the absorption contributions of phytoplankton and colored detrital matter (CDM), as well as the phytoplankton size classes (PSCs), from total minus water absorption spectra. The model is based on three-component separation of phytoplankton size structure and a genetic algorithm. The model performance was tested on two independent datasets (the NASA bio-Optical Marine Algorithm Dataset (NOMAD) and the northern South China Sea (NSCS) dataset). The relationships between the estimated and measured values were strongly linear, especially for a (412), and the Root Mean Square Error (RMSE) of the CDM exponential slope ( S) was relatively low. Next, the inversion model was directly applied to in-situ total minus water absorption spectra determined by an underwater meter during a cruise in September 2008, to retrieve the phytoplankton size structure in the seawater. By comparing the measured and retrieved chlorophyll a concentrations, we demonstrated that total and size-specific chlorophyll a concentrations could be retrieved by the model with relatively high accuracy. Finally, we applied the bio-optical inversion model to investigate changes in phytoplankton size structure induced by an anti-cyclonic eddy in the NSCS. [ABSTRACT FROM AUTHOR]

A previously developed model was modified to derive three phytoplankton size classes (micro-, nano-, and pico-phytoplankton) from the overall chlorophyll- a concentration, assuming that each class has a specific absorption coefficient. The modified model performed well using in-situ data from the northern South China Sea, and the results were reliable and accurate. The relative errors of the size-fractioned chlorophyll- a concentration for each size class were: micro-: 21%, nano-: 41%, pico-: 26%, and nano+pico: 23%. The model was then applied on ocean color remote sensing data to examine the distribution and variation of phytoplankton size classes in northern South China Sea on a large scale. [ABSTRACT FROM AUTHOR]

Using hydrographic data sampled during four successive late summer-early autumn cruises in 2004-2007, vertical stratification along transects in the lee of Taiwan Island was analyzed to investigate upper ocean responses to orographically induced dipole wind stress curl (WSC). Results indicate that mixed-layer depth (MLD) and its relationship with thermocline depth varied under different local wind forcings. Average MLD along the transects from the 2004 to 2007 cruises were 18.5, 30.7, 39.2 and 24.5 m, respectively. The MLD along the transects deepened remarkably and resulted in thermocline ventilation in 2005 and 2006, whereas ventilation did not occur in 2004 and 2007. Estimates indicate that frictional wind speed was the major factor in MLD variations. To a large degree, the combined effects of frictional wind speed and Ekman pumping are responsible for the spatial pattern of MLD during the cruises. [ABSTRACT FROM AUTHOR]

This paper discusses projections of heavy rainfall events in China during the 21st century based on daily precipitation data from the Fourth Assessment Report's (AR4) Coupled General Circulation Models (CGCM). Results show that all three experimental scenarios (scenarios A2, A1B, and B1) project consistent changes in frequency and intensity of heavy rainfall at the end of 21st century. In the regions of Northeast China and North China, there are no significant changes in frequency but there are remarkable increases in intensity of heavy rainfall, indicating that enhanced intensity is the main contributor to increased ratios of heavy rainfall to total annual precipitation in these regions. In regions of the lower reaches of Yangtze River and South China, increases in the amount of heavy rainfall are closely associated with increased frequency and increased intensity. Projected frequencies of heavy rainfall at the end of 21st century increase by 30.9 ∼ 56.6% in the Yangtze River and 35.9 ∼ 50.2% in South China compared to the period of 1980-1999, and projected intensities increase by 1.0 ∼ 5.7% and 2.8 ∼ 6.3%, respectively. Additionally, the ratios of heavy rainfall to total annual precipitation increase by 2.3 ∼ 5.4% in the Yangtze River and 1.8 ∼ 3.8% in South China. The significant increases of heavy rainfall ratios indicate that as the climate warms, heavy rainfall events are expected to increase at rates that are much faster than increases in total precipitation amounts, indicating that China will experience increased amounts of flooding. These results are substantially consistent among the three IPCC (Intergovernmental Panel on Climate Change) scenarios. The increased probability of heavy rainfall events in China is closely connected with increased transportation of water vapour from the Arabian Sea and the South China Sea. Additionally, atmosphere stratification has become increasingly unstable, which has provided a favorable background for the initiation of heavy rainfall at the end of the 21st century. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) genesis over the South China Sea (SCS) during 1965-2004 was analyzed. The locations of TC genesis display evident seasonal changes, with the mean position of formation situated north of 15°N in summer (June-July-August) and south of 15°N in autumn (September-October-November). The TC genesis in summer underwent dramatic interdecadal variations, with more and less TC frequency during 1965-1974/1995-2004 and 1979-1993, respectively. In contrast, a significant interannual variation of TC genesis with a period of ∼4 years was observed in autumn. This study investigated the relationship of SCS TC genesis to the East Asian jet stream (EAJS) and the western North Pacific subtropical high (WNPSH) on an interdecadal time scale. Analysis and comparison of the impacts of the EAJS and the WNPSH on vertical wind shear changes indicate that changes in the WNPSH and EAJS intensity rather than EAJS meridional location are responsible for changes in TC genesis on an interdecadal time scale. Corresponding to a weaker EAJS, anomalous Rossby wave energy at upper levels displays equatorward propagation at midlatitudes and poleward propagation in the subtropics. This induces anomalous convergence and divergence of wave activity fluxes in East Asia around 30°N and the SCS, respectively. The anomalous divergence of wave activity fluxes reduces easterlies at upper levels over the SCS, which is favorable to TC genesis. [ABSTRACT FROM AUTHOR]

The objective of this research is to explore the impacts of El Niño-Southern Oscillation (ENSO) on a possible connection between winter monsoon and summer monsoon over South China. In boreal winter, the strong or weak northerly anomalies due to the East Asian winter monsoon (EAWM), sweep across the continent to the costal regions, which might be favorable for the occurrence of an ENSO event. In boreal summer, South China tends to experience less (more) rainfall and more (less) temperature extremes which might be in the mature phase of a warm (cold) ENSO event. It is also found that more frequent cold surges might be followed by less temperature extremes in the coming year. The possible connection might be that the western Pacific subtropical high after a strong (weak) EAWM year would move northward (southward) through the modification of a ENSO event; this northward (southward) western Pacific subtropical high might result in earlier (later) south China summer monsoon onset and lead to a strong (weak) summer monsoon in the coming year. [ABSTRACT FROM AUTHOR]

Prior studies have revealed that, as a part of the Pacific tropical gyre, the South China Sea throughflow (SCSTF) is strongly influenced by the Pacific low-latitude western boundary current (LLWBC). In this study, ocean general circulation model (OGCM) experiments with and without connection to the South China Sea (SCS) were performed to investigate the impact of the SCSTF on the Pacific LLWBC. These model experiments show that if the SCS is blocked, seasonal variability of the Kuroshio and Mindanao Current becomes stronger, and the meridional migration of the North Equatorial Current (NEC) bifurcation latitude is enhanced. Both in seasonal and interannual time scales, stronger Luzon Strait transport (LST) induces a stronger Kuroshio transport combined with a southward shift of the NEC bifurcation, which is unfavorable for a further increase of the LST; a weaker LST induces a weaker Kuroshio transport and a northward shifting NEC bifurcation, which is also unfavorable for the continuous decrease of the LST. [ABSTRACT FROM AUTHOR]

Ocean colour remote sensing is used as a tool to detect phytoplankton size classes (PSCs). In this study, the Medium Resolution Imaging Spectrometer (MERIS), Moderate Resolution Imaging Spectroradiometer (MODIS), and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) phytoplankton size classes (PSCs) products were compared with in-situ High Performance Liquid Chromatography (HPLC) data for the South China Sea (SCS), collected from August 2006 to September 2011. Four algorithms were evaluated to determine their ability to detect three phytoplankton size classes. Chlorophyll-a (Chl-a) and absorption spectra of phytoplankton (aph(λ)) were also measured to help understand PSC’s algorithm performance. Results show that the three abundance-based approaches performed better than the inherent optical property (IOP)-based approach in the SCS. The size detection of microplankton and picoplankton was generally better than that of nanoplankton. A three-component model was recommended to produce maps of surface PSCs in the SCS. For the IOP-based approach, satellite retrievals of inherent optical properties and the PSCs algorithm both have impacts on inversion accuracy. However, for abundance-based approaches, the selection of the PSCs algorithm seems to be more critical, owing to low uncertainty in satellite Chl-a input data [ABSTRACT FROM AUTHOR]

Abstract: Analyses of tropical cyclone (TC) occurrence dates in the South China Sea (SCS) for the past 60 yrs indicate a trend toward an earlier occurrence of the first annual TC in the SCS. On the other hand, a significant increasing trend in sea surface temperature (SST) in early summer (May–June) has been observed in the SCS. The negative correlation between the first annual TC occurrence date and SST in early summer during the period 1945–2009 suggests that the earlier occurrence of the first annual TC is related not only to the increasing of SST in the SCS, but also to the variability of SST in the Niño3.4 region. Quantitative analysis of the SCS TC occurrence date and SST by quantile regression also reveals such a relationship and confirms that the SCS early-season TCs tend to occur earlier when SSTs in the SCS and Niño3.4 region are increasing. Since the SCS SST anomalies are influenced by the El Niño-Southern Oscillation (ENSO), the relationship between the first annual TC occurrence date and ENSO-related large-scale atmospheric circulation including 850-hPa relative vorticity (RV), vertical wind shear (VWS), and moist static energy (MSE) in early summer are also investigated. It is found that variations of VWS and MSE have influences on first annual SCS TC occurrence dates, although there is not a statistically significant relationship between 850-hPa RV and first annual SCS TC occurrence date. These results suggest that the earlier occurrence of the first annual TC in the SCS is influenced not only by local SST, but also by ENSO through the alternation of early summer VWS and MSE in the SCS. [Copyright &y& Elsevier]

Abstract: The interannual variability of upper ocean heat content (OHC) in the South China Sea (SCS) for the period of 1987–2006 and its response to ENSO events are investigated. It is found that the variability has a good correspondence with ENSO events, but with opposite phase. Negative OHC anomalies appear during ENSO warm phases, while positive OHC anomalies occur during ENSO cool phases. In addition, negative (positive) OHC anomalies propagate westward obviously during ENSO warm (cool) phases in the northern SCS. In contrast, OHC anomalies in the southern SCS do not exhibit distinct westward propagation during ENSO events. To explore why the OHC anomalies cannot propagate westward in the southern SCS, the interannual variability of oceanic and atmospheric anomaly fields including wind stress curl (WSC), horizontal wind stress, latent heat flux (LHF) and sea level pressure (SLP) is investigated. The results show that after a mature phase of ENSO warm (cool) event, negative (positive) OHC anomalies first appear in the northern SCS, which comes from the western Pacific through Luzon Strait. Then cyclonic (anticyclonic) wind stress anomalies occur in the northern SCS, which leads to positive (negative) WSC anomalies. Meanwhile, positive (negative) LHF anomalies which correspond to oceanic heat loss (gain) occur in this region. The effects of WSC and LHF, combined with the westward propagating negative (positive) OHC anomalies from the western Pacific, may contribute to rapid growth and propagation of the OHC anomalies in the northern SCS. On the contrary, the negative (positive) WSC and LHF anomalies associated with positive (negative) SLP in the southern SCS seem to be the important processes responsible for the weakening and non-propagation of the OHC anomalies in the southern SCS after a mature phase of ENSO warm (cool) event. [Copyright &y& Elsevier]