基于多源融合卫星高度计观测数据的南海海浪有效波高的季节变化研究

The seasonal variability of the significant wave height(SWH) in the South China Sea(SCS) is investigated using the most up-to-date gridded daily altimeter data for the period of September 2009 to August 2015. The results indicate that the SWH shows a uniform seasonal variation in the whole SCS, with its maxima occurring in December/January and minima in May. Throughout the year, the SWH in the SCS is the largest around Luzon Strait(LS) and then gradually decreases southward across the basin. The surface wind speed has a similar seasonal variation, but with different spatial distributions in most months of the year. Further analysis indicates that the observed SWH variations are dominated by swell. The wind sea height, however, is much smaller. It is the the largest in two regions southwest of Taiwan Island and southeast of Vietnam Coast during the northeasterly monsoon, while the largest in the central/southern SCS during the southwesterly monsoon. The extreme wave condition also experiences a significant seasonal variation. In most regions of the northern and central SCS, the maxima of the 99 th percentile SWH that are larger than the SWH theoretically calculated with the wind speed for the fully developed seas mainly appear in August–November, closely related to strong tropical cyclone activities.Compared with previous studies, it is also implied that the wave climate in the Pacific Ocean plays an important role in the wave climate variations in the SCS.     

Impacts of a wind stress and a buoyancy flux on the seasonal variation of mixing layer depth in the South China Sea

The seasonal variation of mixing layer depth(MLD) in the ocean is determined by a wind stress and a buoyance flux.A South China Sea(SCS) ocean data assimilation system is used to analyze the seasonal cycle of its MLD.It is found that the variability of MLD in the SCS is shallow in summer and deep in winter,as is the case in general.Owing to local atmosphere forcing and ocean dynamics,the seasonal variability shows a regional characteristic in the SCS.In the northern SCS,the MLD is shallow in summer and deep in winter,affected coherently by the wind stress and the buoyance flux.The variation of MLD in the west is close to that in the central SCS,influenced by the advection of strong western boundary currents.The eastern SCS presents an annual cycle,which is deep in summer and shallow in winter,primarily impacted by a heat flux on the air-sea interface.So regional characteristic needs to be cared in the analysis about the MLD of SCS.     

路经南海热带气旋迅速加强的年代际变化

本文利用中国气象局热带气旋资料中心最佳路径数据集、美国国家环境预报中心/美国国家大气研究中心大气再分析数据集和国家海洋信息中心的海洋再分析数据集,研究了路经南海热带气旋迅速加强(Rapid Intensification, RI)的年代际变化。在1951–2017年期间,路经南海的热带气旋主要发生在6–12月,其中发生RI的热带气旋集中在7–12月,且RI呈现年代际变化,这种变化和太平洋年代际振荡(Pacific Decadal Oscillation, PDO)显著相关。在正PDO年,RI频数较少且主要分布在菲律宾群岛东部和南海北部;而在负PDO年,RI频数较多且分布在菲律宾群岛东部的大范围区域。路经南海热带气旋RI的年代际变化与PDO对大尺度海洋大气变量的调制有关。回归分析显示热带气旋潜热对路经南海热带气旋RI频数的年代际变化影响最大,而相对湿度的影响相对较小,垂直风切变的影响很小。     

LICOM模拟的南海贯穿流及其对南海上层热含量的影响

利用SODA(Simple Ocean Data Assimilation)数据、XBT(Expendable Bathythermograph)观测数据和绕岛环流理论(island rule)诊断计算结果评估了一个涡相容(eddy-permitting)全球海洋环流模式——LICOM对南海贯穿流及南海上层热含量的模拟能力,同时利用模式输出探讨了南海贯穿流对南海上层热含量的影响。NEC(North Equatorial Current)分叉的垂向结构、南海内区环流的季节和吕宋海峡体积输送的年际变化等分析结果都表明,LICOM能获取西北太平洋-印尼海域环流和南海贯穿流的合理模拟结果。模式模拟的南海上层热含量季节变化与观测及同化数据都表现出良好的一致性,尤其在南海内区。相关分析表明,吕宋海峡热输送主要控制着南海内区上层的热含量变化,两者呈显著负相关,这进一步证实了南海贯穿流作为一支冷平流调制着南海上层热含量变化的重要事实。     

The characteristic differences of tropical cyclones forming over the western North Pacific and the South China Sea

The best track dataset of tropical cyclones in the western North Pacific (WNP) and the South China Sea (SCS) from 1977 to 2005 during the satellite era, the NCEP/NCAR reanalysis dataset and the extended reconstructed sea surface temperature dataset are employed in this study. The main climatological characteristics of tropical cyclone formation over the WNP and the SCS are compared. It is found that there is obviously different for the locations of tropical cyclone origins, achieving the lowest central pressure and termination points between over the WNP and over the SCS. The annual number of tropical cyclones forming over the SCS is obviously less than over the WNP, and there is a significant negative correlation with the correlation coefficient being -0.36 at the 5% significance level between over the WNP and over the SCS. The mean speed of tropical cyclone moving is 6.5 m /s over the WNP and 4.6 m /s over the SCS. The mean lowest central pressure of tropical cyclones is obviously weaker over the SCS than over the WNP. The tropical cyclone days per year, mean total distance and total displacement of tropical cyclone traveled over the WNP are all obviously longer than those over the SCS. Tropical cyclone may intensify to Saffir-Simpson hurricane scale 5 over the WNP, but no tropical cyclone can intensify to Saffir-Simpson hurricane scale 3 over the SCS. The changing ranges of the radii(R15,R16) of the 15.4 m /s winds them and the 25.7 m /s winds over the WNP are obviously wider than those over the SCS, and the median values of the radii over the WNP are also larger than those over the SCS. For the same intensity of tropical cyclones, both radii have larger medians over the WNP than over the SCS. The correlations of annual mean tropical cyclone size parameters between over the WNP and over the SCS are not significant. At the same time, the asymmetric radii of tropical cyclones over the WNP are different from those over the SCS.     

基于ROMS模式利用集合最优插值同化沿轨海表面高度异常数据的研究

The ensemble optimal interpolation （EnOI） is applied to the regional ocean modeling system （ROMS） with the ability to assimilate the along-track sea level anomaly （TSLA）. This system is tested with an eddy-resolving system of the South China Sea （SCS）. Background errors are derived from a running seasonal ensemble to account for the seasonal variability within the SCS. A fifth-order localization function with a 250 km localization radius is chosen to reduce the negative effects of sampling errors. The data assimilation system is tested from January 2004 to December 2006. The results show that the root mean square deviation （RMSD） of the sea level anomaly decreased from 10.57 to 6.70 cm, which represents a 36.6% reduction of error. The data assimilation reduces error for temperature within the upper 800 m and for salinity within the upper 200 m, although error degrades slightly at deeper depths. Surface currents are in better agreement with trajectories of surface drifters after data assimilation. The variance of sea level improves significantly in terms of both the amplitude and position of the strong and weak variance regions after assimilating TSLA. Results with AGE error （AGE） perform better than no AGE error （NoAGE） when considering the improvements of the temperature and the salinity. Furthermore, reasons for the extremely strong variability in the northern SCS in high resolution models are investigated. The results demonstrate that the strong variability of sea level in the high resolution model is caused by an extremely strong Kuroshio intrusion. Therefore, it is demonstrated that it is necessary to assimilate the TSLA in order to better simulate the SCS with high resolution models.     

南海沿海季节性海平面异常变化特征及成因分析

Based on sea level, air temperature, sea surface temperature(SST), air pressure and wind data during 1980–2014,this paper uses Morlet wavelet transform, Estuarine Coastal Ocean Model(ECOM) and so on to investigate the characteristics and possible causes of seasonal sea level anomalies along the South China Sea(SCS) coast. The research results show that:(1) Seasonal sea level anomalies often occur from January to February and from June to October. The frequency of sea level anomalies is the most in August, showing a growing trend in recent years. In addition, the occurring frequency of negative sea level anomaly accounts for 50% of the total abnormal number.(2) The seasonal sea level anomalies are closely related to ENSO events. The negative anomalies always occurred during the El Ni?o events, while the positive anomalies occurred during the La Ni?a(late El Ni?o) events. In addition, the seasonal sea level oscillation periods of 4–7 a associated with ENSO are the strongest in winter, with the amplitude over 2 cm.(3) Abnormal wind is an important factor to affect the seasonal sea level anomalies in the coastal region of the SCS. Wind-driven sea level height(SSH) is basically consistent with the seasonal sea level anomalies. Moreover, the influence of the tropical cyclone in the coastal region of the SCS is concentrated in summer and autumn, contributing to the seasonal sea level anomalies.(4) Seasonal variations of sea level, SST and air temperature are basically consistent along the coast of the SCS, but the seasonal sea level anomalies have no much correlation with the SST and air temperature.     

Sub-seasonal variability of Luzon Strait Transport in a high resolution global model

The Luzon Strait is the main impact pathway of the Kuroshio on the circulation in South China Sea (SCS). Based on the analysis of the 1997–2007 altimeter data and 2005–2006 output data from a high resolution global HYCOM model, the total Luzon Strait Transport (LST) has remarkable subseasonal oscillations with a typical period of 90 to 120 days, and an average value of 1.9 Sv into SCS. Further spectrum analysis shows that the temporal variability of the LST at different depth is remarkable different. In the upper layer (0–300 m), westward inflow has significant seasonal and subseasonal variability. In the bottom layer (below 1 200 m), eastward outflow exhibits remarkable seasonal variability, while subseasonal variability is also clear. In the intermediate layer, the westward inflow is slightly bigger than the eastward outflow, and both of them have obvious seasonal and subseasonal variability. Because the seasonal variation of westward inflow and eastward outflow is opposite, the total transport of intermediate layer exhibits significant 50–150 days variation, without obvious seasonal signals. The westward Rossby waves with a period of 90 to 120 days in the Western Pacific have very clear correlationship with the Luzon Strait Transport, this indicates that the interaction between these westward Rossby waves and Kuroshio might be the possible mechanism of the subseasonal variation of the LST.     

“21世纪海上丝绸之路”风能资源时空变化评估

利用1979—2021 年的 ERA5 再分析资料,采用经验正交函数分解法、Mann-Kendall 趋势检验法等统计方法,对“21 世纪海上丝绸之路”相关海区的海表风场与风能密度的空间分布特征、季节变化特征以及长期变化趋势进行分析。结果表明：(1)研究海域风能密度在不同季节表现出很大的空间差异,夏季的阿拉伯海和孟加拉湾,冬季的中国南海,以及全年的热带南印度洋风能资源都极为丰富。(2)研究时段内,中国南海北部及附近海域、阿拉伯海西部、孟加拉湾西部以及热带西北印度洋风能密度等级整体较高。(3)研究海域的风能密度以年变化特征为主,其中中国南海风能密度的季节变幅最大且在春、秋两季表现出明显的转换特征。(4)在研究海区中,结合水深条件与风能密度时空变化特征的评估结果,可以重点关注台湾海峡、吕宋海峡、中南半岛东南沿海、阿拉伯海西部近岸海域及热带西北印度洋近岸大陆架海域风能资源的开发利用,加强其他海域风能资源的储备。此研究可为“21 世纪海上丝绸之路”风能资源的中长期开发规划提供依据。     

南海深水海盆环流和温跃层深度的季节变化

受南海季风和复杂地形的影响,南海环流场具有复杂的空间结构和明显的季节变化,同时此海域又是中尺度涡多发海域,这些特征必然对南海温跃层深度的水平分布及季节变化有显著影响。首先,基于GDEM(General-ized Digital Environmental Model)的温、盐资料和利用P矢量方法计算并分析了南海的表层环流和多涡结构的空间分布特征和季节变化规律。在此基础上,分析了南海温跃层深度的空间分布特征和季节变化规律。结果表明,南海环流和多涡结构对南海温跃层具有显著的影响。     

对吕宋海峡深水瀑布的重新认识

On the basis of the latest version of a U.S. Navy generalized digital environment model(GDEM-V3.0) and World Ocean Atlas(WOA13), the hydraulic theory is revisited and applied to the Luzon Strait, providing a fresh look at the deepwater overflow there. The result reveals that:(1) the persistent density difference between two sides of the Luzon Strait sustains an all year round deepwater overflow from the western Pacific to the South China Sea(SCS);(2) the seasonal variability of the deepwater overflow is influenced not only by changes in the density difference between two sides of the Luzon Strait, but also by changes in its upstream layer thickness;(3) the deepwater overflow in the Luzon Strait shows a weak semiannual variability;(4) the seasonal mean circulation pattern in the SCS deep basin does not synchronously respond to the seasonality of the deepwater overflow in the Luzon Strait.Moreover, the deepwater overflow reaches its seasonal maximum in December(based on GDEM-V3.0) or in fall(October–December, based on the WOA13), accompanied by the lowest temperature of the year on the Pacific side of the Luzon Strait. The seasonal variability of the deepwater overflow is consistent with the existing longest(3.5 a) continuous observation along the major deepwater passage of the Luzon Strait.     

Local origins of interdecadal Pacific variability in the tropical and North Pacific Ocean: evidence from a comparative study of coral oxygen isotope records

Interdecadal Pacific variability (IPV) is commonly observed in both the tropical and mid-latitude Pacific Ocean, and has a widespread influence on surface climate in the Pan-Pacific Basin. This variability is recorded by climate proxies such as geochemical parameters preserved in corals. However, the origins of IPV remain uncertain. To shed light on this, interdecadal variations in two long coral δ¹⁸O records from Nauru Island and the South China Sea (SCS), respectively located in the tropical Pacific and the mid-latitude North Pacific Ocean, were investigated. The interdecadal fluctuations in the δ¹⁸O series from Nauru Island (tropical Pacific) match those of the NINO3.4 index reasonably well (r=–0.30, n=96, p=0.0015), but are not correlated with those of the Pacific decadal oscillation (PDO) index (r=–0.17, n=96, p=0.05). The δ¹⁸O time series from the SCS (northwestern Pacific), by contrast, co-vary with the PDO index (r=–0.30, n=156, p=0.0007), but are out of phase with the NINO3.4 index at the interdecadal timescale (r=0.04, n=156, p=0.31). The impact on the interdecadal variability of processes occurring outside the growth region of corals is generally weak. The results thus do not support a tropical origin of IPV, but demonstrate that the interdecadal variability in the tropical Pacific and the North Pacific originates predominantly from local coupled ocean–atmosphere processes within these regions. The results also suggest that tropical–extratropical interactions played a role in IPV between 1920 and 1940, which indicates that IPV is a complex climatic phenomenon that involves multiple forcing mechanisms.     

The influence of 30~60 d oscillation on the development of the South China Sea summer monsoon

Using the National Center for Enviromental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and NOAA satellite-obser ved outgoing long-wave radiation (OLR) data, the development of the South China Sea (SCS) summer monsoon and intraseasonal (30-60 d) oscillation (ISO) have been examined. The results show that there exists obvious interannual variability of intraseasonal oscillaiton. Using the 16 a time series of filtered OLR averaged over the SCS, an index is defined to define ““onset events““ over the SCS on the ISO time scales. Of the 16 a examined here, 10 shows a strong ISO signal in the onset of monsoon convection over the SCS. In these cases, the ISO initially suppresses the seasonal development of southwesterly and cyclonic circulation over the SCS before the ISO onset. As the ISO propagates northeastward, the low frequency cyclonic circulation anomaly occurs in the SCS and the low frequency southwesterly wind and convection over here dramatically intensify. The northeast progression of the ISO anomaleis plays a role in the initial suppression and then acceleration of the seasonal cycle of the SCS summer monsoon.     

Recent progress in studies of the South China Sea circulation

The South China Sea (SCS) is a semi-enclosed marginal sea with deep a basin. The SCS is located at low latitudes, where the ocean circulations are driven principally by the Asia-Australia monsoon. Ocean circulation in the SCS is very complex and plays an important role in both the marine environment and climate variability. Due to the monsoon-mountain interactions the seasonal spatial pattern of the sea surface wind stress curl is very specific. These distinct patterns induce different basin-scale circulation and gyre in summer and winter, respectively. The intensified western boundary currents associated with the cyclonic and anticyclonic gyres in the SCS play important roles in the sea surface temperature variability of the basin. The mesoscale eddies in the SCS are rather active and their formation mechanisms have been described in recent studies. The water exchange through the Luzon Strait and other straits could give rise to the relation between the Pacific and the SCS. This paper reviews the research results mentioned above.     

Seasonal and interannual variability of carbon cycle in South China Sea: A three-dimensional physical-biogeochemical modeling study

The South China Sea (SCS) exhibits strong variations on seasonal to interannual time scale, and the changing Southeast Asian Monsoon has direct impacts on the nutrients and phytoplankton dynamics, as well as the carbon cycle. A Pacific basin-wide physical-biogeochemical model has been developed and used to investigate the physical variations, ecosystem responses, and carbon cycle consequences. The Pacific basin-wide circulation model, based on the Regional Ocean Model Systems (ROMS) with a 50-km spatial resolution, is driven with daily air-sea fluxes derived from the National Centers for Environmental Prediction (NCEP) reanalysis between 1990 and 2004. The biogeochemical processes are simulated with the Carbon, Si(OH)₄, Nitrogen Ecosystem (CoSINE) model consisting of multiple nutrients and plankton functional groups and detailed carbon cycle dynamics. The ROMS-CoSINE model is capable of reproducing many observed features and their variability over the same period at the SouthEast Asian Time-series Study (SEATS) station in the SCS. The integrated air-sea CO₂ flux over the entire SCS reveals a strong seasonal cycle, serving as a source of CO₂ to the atmosphere in spring, summer and autumn, but acting as a sink of CO₂ for the atmosphere in winter. The annual mean sea-to-air CO₂ flux averaged over the entire SCS is +0.33 moles CO₂ m⁻²year⁻¹, which indicates that the SCS is a weak source of CO₂ to the atmosphere. Temperature has a stronger influence on the seasonal variation of pCO₂ than biological activity, and is thus the dominant factor controlling the oceanic pCO₂ in the SCS. The water temperature, seasonal upwelling and Kuroshio intrusion determine the pCO₂ differences at coast of Vietnam and the northwestern region of the Luzon Island. The inverse relationship between the interannual variability of Chl-a in summer near the coast of Vietnam and NINO₃ SST (Sea Surface Temperature) index in January implies that the carbon cycle and primary productivity in the SCS is teleconnected to the Pacific-East Asian large-scale climatic variability.     

台风威马逊入侵南海的路径分析

1409号台风威马逊是自1973年以来登陆华南地区的最强台风,其在登陆前,临岸急剧增强。每年初夏,尽管南海的海洋环境有利于台风的增长,但是由于西太平洋副热带高压(以下简称副高)的引导作用,大部分台风路径会偏离南海。本文分析结果表明,在2014年初夏,副高的位置相对过去几十年的平均位置更偏向西南方,因此,台风威马逊在副高的引导下穿过菲律宾进入南海海域。南海的高温海水为其强度陡增提供了有利条件,威马逊在短短26 h内急剧增长为超强台风。前人研究结果显示,近些年来副高的位置明显向西延伸,如果这种西向延伸的趋势一直保持或者继续,那么在初夏可能会有更多的热带风暴进入南海并且得以加强,华南地区或将面临更多灾难性台风的袭击。     

Patterns of upper layer circulation variability in the South China Sea from satellite altimetry using the self-organizing map

Patterns of the South China Sea (SCS) circulation variability are extracted from merged satellite altimetry data from October 1992 through August 2004 by using the self-organizing map (SOM). The annual cycle, seasonal and inter-annual variations of the SCS surface circulation are identified through the evolution of the characteristic circulation patterns. The annual cycle of the SCS gener- al circulation patterns is described as a change between two opposite basin-scale SW-NE oriented gyres embedded with eddies: low sea surface height anomaly (SSHA) (cyclonic) in winter and high SSHA (anticyclonic) in summer half year. The transition starts from July--August (January--February) with a high (low) SSHA tongue east of Vietnam around 12°～14° N, which de- velopa into a big anticyclonic (cyclonic) gyre while moving eastward to the deep basin. During the transitions, a dipole structure, cyclonic (anticyclonic) in the north and anticyclonic (cyclonic) in the south, may be formed southeast off Vietnam with a strong zonal jet around 10°～12° N. The seasonal variation is modulated by the interannual variations. Besides the strong 1997/1998 e- vent in response to the peak Pacific El Nino in 1997, the overall SCS sea level is found to have a significant rise during 1999～ 2001, however, in summer 2004 the overall SCS sea level is lower and the basin-wide anticyclonic gyre becomes weaker than the other years.     

南海暖水季节和年际变化的初步研究

南海暖水具有明显的季节和年际变化。利用气候平均的COADS资料和NCEP大气资料分析了南海暖水的季节变化及其与海面净热通量的关系,以及由此引起的南海地区大气环流的变化。发现海面净热通量在南海暖水的季节变化过程中起到了主要的作用;冬季无暖水存在时,最大上升气流位于赤道及以南地区的印尼群岛附近,夏季最大上升气流北移到了南海暖水上空,南海暖水上空对流强烈,成为大气的对流活动中心。利用50年逐月的SODA海温资料进行垂直方向的3次样条插值,定义并计算南海暖水的强度指数,分析南海暖水的年际变化,并对南海暖水的几个异常暖年份作了合成分析,探讨了暖水年际变化的形成因素。     

Modeling the long-term variability of phytoplankton functional groups and primary productivity in the South China Sea

Primary productivity (PP) and phytoplankton structure play an important role in regulating oceanic carbon cycle. The unique seasonal circulation and upwelling pattern of the South China Sea (SCS) provide an ideal natural laboratory to study the response of nutrients and phytoplankton dynamics to climate variation. In this study, we used a three-dimensional (3D) physical–biogeochemical coupled model to simulate nutrients, phytoplankton biomass, PP, and functional groups in the SCS from 1958 to 2009. The modeled results showed that the annual mean carbon composition of small phytoplankton, diatoms, and coccolithophores was 33.7, 52.7, and 13.6 %, respectively. Diatoms showed a higher seasonal variability than small phytoplankton and coccolithophores. Diatoms were abundant during winter in most areas of the SCS except for the offshore of southeastern Vietnam, where diatom blooms occurred in both summer and winter. Higher values of small phytoplankton and coccolithophores occurred mostly in summer. Our modeled results indicated that the seasonal variability of PP was driven by the East Asian Monsoon. The northeast winter monsoon results in more nutrients in the offshore area of the northwestern Luzon Island and the Sunda Shelf, while the southwest summer monsoon drives coastal upwelling to bring sufficient nutrients to the offshore area of southeastern Vietnam. The modeled PP was correlated with El Niño/Southern Oscillation (ENSO) at the interannual scale. The positive phase of ENSO (El Niño conditions) corresponded to lower PP and the negative phase of ENSO (La Niña conditions) corresponded to higher PP.     

基于ROMS模型数值研究南海温跃层的季节变化

On the basis of the regional ocean modeling system （ROMS）, the seasonal variations of the thermocline in the South China Sea （SCS） were numerically investigated. The simulated hydrodynamics are in accordance with previous studies： the circulation pattern in the SCS is cyclonic in winter and anticyclonic in summer, and such a change is mostly driven by the monsoon winds. The errors between the modeled temperature profiles and the observations obtained by cruises are quite small in the upper layers of the ocean, indicating that the ocean status is reasonably simulated. On the basis of the shapes of the vertical temperature profiles, five thermocline types （shallow thermocline, deep thermocline, hybrid thermocline, double thermocline, and multiple thermocline） are defined herein. In winter, when the northeasterly monsoon prevails, most shallow shelf seas in the northwest of the SCS are well mixed, and there is no obvious thermocline. The deep region generally has a deep thermocline, and the hybrid or double thermocline often occurs in the areas near the cold eddy in the south of the SCS. In summer, when the southwesterly monsoon prevails, the shelf sea area with a shallow thermocline greatly expands. The distribution of different thermocline types shows a relationship with ocean bathymetry： from shallow to deep waters, the thermocline types generally change from shallow or hybrid to deep thermocline, and the double or multiple thermocline usually occurs in the steep regions. The seasonal variations of the three major thermocline characteristics （the upper bound depth, thickness, and intensity） are also discussed. Since the SCS is also an area where tropical cyclones frequently occur, the response of thermocline to a typhoon process in a short time scale is also analyzed.