Interocean circulation and heat and freshwater budgets of the South China Sea based on a numerical model

The South China Sea (SCS) interocean circulation and its associated heat and freshwater budgets are examined using the results of a variable-grid global ocean model. The ocean model has a 1/6° resolution in the SCS and its adjacent oceans. The model results from 1982 to 2003 show that the western Pacific waters enter the SCS through the Luzon Strait with an annual mean volume transport of 4.80 Sv, of which 1.71 Sv returns to the western Pacific through the Taiwan Strait and East China Sea and 3.09 Sv flows toward the Indian Ocean. The heat in the western Pacific is transported to the SCS with a rate of 0.373 PW (relative to a reference temperature 3.72 °C), while the total heat transport through the outflow straits is 0.432 PW. The net heat transport out of the SCS is thus 0.059 PW, which is balanced by a mean net downward heat flux of 17 W/m² across the SCS air–sea interface. Therefore, the interocean circulation acts as an “air conditioner”, cooling the SCS and its overlaying atmosphere. The SCS contributes a heat transport of 0.279 PW to the Indian Ocean, of which 0.240 PW is from the Pacific Ocean through the Luzon Strait and 0.039 PW is from the SCS interior gained from the air–sea exchange. The Luzon Strait salt transport is greater than the total salt transport leaving the SCS by 3.97 Gg/s, implying a mean freshwater flux of 0.112 Sv (or 3.54 × 10¹² m³/year) from the land discharge and P − E (precipitation minus evaporation). The total annual land discharge to the SCS is estimated to be 1.60 × 10¹² m³/year, the total annual P − E over the SCS is thus 1.94 × 10¹² m³/year, equivalent to a mean P − E of 0.55 m/year. The SCS freshwater contribution to the Indian Ocean is 0.096 Sv. The pattern of the SCS interocean circulation in winter differs greatly from that in summer. The SCS branch of the Pacific-to-Indian Ocean throughflow exists in winter, but not in summer. In winter this branching flow starts at the Luzon Strait and extends to the Karimata Strait. In summer the interocean circulation is featured by a north-northeastward current starting at the Karimata Strait and extending to the Taiwan and Luzon Straits, and a subsurface inflow from the Luzon Strait that upwells into the surface layer in the SCS interior to supply the outward transports.     

The seasonal variation of the upper layers of the South China Sea (SCS) circulation and the Indonesian through flow (ITF): An ocean model study

The upper layer, wind-driven circulation of the South China Sea (SCS), its through-flow (SCSTF) and the Indonesian through flow (ITF) are simulated using a high resolution model, FVCOM (finite volume coastal ocean model) in a regional domain comprising the Maritime Continent. The regional model is embedded in the MIT global ocean general circulation model (ogcm) which provides surface forcing and boundary conditions of all the oceanographic variables at the lateral open boundaries in the Pacific and Indian oceans. A five decade long simulation is available from the MITgcm and we choose to investigate and compare the climatologies of two decades, 1960–1969 and 1990–1999.The seasonal variability of the wind-driven circulation produced by the monsoon system is realistically simulated. In the SCS the dominant driving force is the monsoon wind and the surface circulation reverses accordingly, with a net cyclonic tendency in winter and anticyclonic in summer. The SCS circulation in the 90s is weaker than in the 60s because of the weaker monsoon system in the 90s. In the upper 50 m the interaction between the SCSTF and ITF is very important. The southward ITF can be blocked by the SCSTF at the Makassar Strait during winter. In summer, part of the ITF feeds the SCSTF flowing into the SCS through the Karimata Strait. Differently from the SCS, the ITF is primarily controlled by the sea level difference between the western Pacific and eastern Indian Ocean. The ITF flow, consistently southwestward below the surface layer, is stronger in the 90s.The volume transports for winter, summer and yearly are estimated from the simulation through all the interocean straits. On the annual average, there is a ∼5.6 Sv of western Pacific water entering the SCS through the Luzon Strait and ∼1.4 Sv exiting through the Karimata Strait into the Java Sea. Also, ∼2 Sv of SCS water enters the Sulu Sea through the Mindoro Strait, while ∼2.9 Sv flow southwards through the Sibutu Strait merging into the ITF. The ITF inflow occurs through the Makassar Strait (up to ∼62%) and the Lifamatola Strait (∼38%). The annual average volume transport of the ITF inflow from the simulation is ∼15 Sv in the 60s and ∼16.6 Sv in the 90s, very close to the long term observations. The ITF outflow through the Lombok, Ombai and Timor straits is ∼16.8 Sv in the 60s and 18.9 Sv in the 90s, with the outflow greater by 1.7 Sv and 2.3 Sv respectively. The transport estimates of the simulation at all the straits are in rather good agreement with the observational estimates.We analyze the thermal structure of the domain in the 60s and 90s and assess the simulated temperature patterns against the SODA reanalysis product, with special focus on the shallow region of the SCS. The SODA dataset clearly shows that the yearly averaged temperatures of the 90s are overall warmer than those of the 60s in the surface, intermediate and some of the deep layers and the decadal differences (90s − 60s) indicate that the overall warming of the SCS interior is a local effect. In the simulation the warm trend from the 60s to the 90s in well reproduced in the surface layer. In particular, the simulated temperature profiles at two shallow sites at midway in the SCSTF agree rather well with the SODA profiles. However, the warming trend in the intermediate (deep) layers is not reproduced in the simulation. We find that this deficiency is mostly due to a deficiency in the initial temperature fields provide by the MITgcm.     

Impacts of the South China Sea Throughflow on seasonal and interannual variations of the Indonesian Throughflow

Impacts of the South China Sea Throughflow (SCST) on seasonal and interannual variations of the Indonesian Throughflow are studied by comparing outputs from ocean general circulation model (OGCM) experiments with and without the SCST. The observed subsurface maximum in the southward flow through the Makassar Strait is simulated only when the SCST, which is driven by the large-scale wind, is allowed in the model. The mean volume and heat transport by the Makassar Strait Throughflow are reduced by 1.7 Sv and 0.19 PW, respectively, by the existence of the SCST in the model. The difference is particularly remarkable during boreal winter when the SCST reaches its seasonal maximum. Furthermore, the SCST is strengthened during El Niño, leading to the weakening in the southward volume and heat transport through the Makassar Strait by 0.37 Sv and 0.05 PW, respectively. These findings from the OGCM experiments suggest that the SCST may play an important role in climate variability of the Indo-Pacific Ocean.     

Annual variation of the southern boundary current in the Banda Sea

ADCP measurements in the southern Banda Sea, obtained with the bulk carrier “MS First Jupiter” from 1997 until 2000, have been analysed. The observations reveal the presence of an eastward flowing southern boundary current, bringing water from the Indonesian throughflow towards the connections with the Indian Ocean in Ombai Strait and the Timor Sea. The mean transport in the upper 300 m is estimated to be about 5 Sv, over 50% of the outflow towards the Indian Ocean in this layer through the eastern passages near Timor. The velocity in the boundary current shows a clear annual variation, more or less in phase with the annually varying inflow through Makassar Strait and the outflow near Timor. The phase of the annual variation cannot be explained by the monsoonal variation of the local winds. Therefore this annual variation of the throughflow is probably generated by large-scale forcing. A considerable reduction of the strength of the boundary current was observed in 1998, following the 1997–1998 El Niño with a delay of about half a year. On shorter time scales, Kelvin waves, entering the Banda Sea from the Indian Ocean, cause flow reversals of the boundary current.     

Simulated and observed circulation in the Indonesian Seas: 1/12° global HYCOM and the INSTANT observations

A 1/12° global version of the HYbrid Coordinate Ocean Model (HYCOM) using 3-hourly atmospheric forcing is analyzed and directly compared against observations from the International Nusantara STratification ANd Transport (INSTANT) program that provides the first long-term (2004–2006) comprehensive view of the Indonesian Throughflow (ITF) inflow/outflow and establishes an important benchmark for inter-basin exchange, including the net throughflow transport. The simulated total ITF transport (−13.4 Sv) is similar to the observational estimate (−15.0 Sv) and correctly distributed among the three outflow passages (Lombok Strait, Ombai Strait and Timor Passage). Makassar Strait carries ∼75% of the observed total ITF inflow and while the temporal variability of the simulated transport has high correlation with the observations, the simulated mean volume transport is ∼37% too low. This points to an incorrect partitioning between the western and eastern inflow routes in the model and is the largest shortcoming of this simulation. HYCOM simulates the very deep (>1250 m) overflow at Lifamatola Passage (−2.0 Sv simulated vs. −2.5 Sv observed) and indicates overflow contributions originating from the North (South) Equatorial Current in boreal winter–spring (summer–autumn). A new finding of INSTANT is the mean eastward flow from the Indian Ocean toward the interior Indonesian Seas on the north side of Ombai Strait. This flow is not robustly simulated at 1/12° resolution, but is found in a 1/25° version of global HYCOM using climatological forcing, indicating the importance of horizontal resolution. However, the 1/25° model also indicates that the mean eastward flow retroflects, turning back into the main southwestward Ombai Strait outflow, and in the mean does not enter the interior seas to become part of the water mass transformation process. The 1/12° global HYCOM is also used to fill in the gaps not measured as part of the INSTANT observational network. It indicates the wide and shallow Java and Arafura Seas carry −0.8 Sv of inflow and that the three major outflow passages capture nearly all the total Pacific to Indian Ocean throughflow.     

Three inflow pathways of the Indonesian throughflow as seen from the simple ocean data assimilation

The SODA product is used to investigate three Indonesian throughflow (ITF) branches: the flow through the Makassar Strait; through the South China Sea; and through the eastern Indonesian basins. The results reveal strong interannual variation in the Makassar Strait and the eastern Indonesian basins throughflow. Inspection of vertically integrated dynamic height (0–1000 db), a proxy of transport function, suggests that this interannual variation can be traced to the New Guinea Coastal Current, indicative of a strong influence of the South Pacific. The vertically integrated dynamic height along the south Java coast is related to variation in the North Pacific and in particular near the east coast of Mindanao Island, whereas the vertically integrated dynamic height along the coast of West Australia is related to variation in the South Pacific, and in particular near the coast of New Guinea. The integrated dynamic height difference between the Java and New Guinea coast appears to be a good proxy of ITF transport on the interannual time scale. Regression analysis shows a phase dependence of the three ITF pathways on the Nino3.4 index. Decoupling of current anomalies between the surface and subsurface layers is identified in the developing and mature phase of El Nino, reflecting different effects of local and remote forcing through oceanic pathways at the Makassar Strait and eastern Indonesian basins.     

Interpretation of interbasin exchange in an isopycnal ocean model

 This work concerns an analysis of inter-basin and inter-layer exchanges in the component ocean part of the coupled ECHAM4/OPYC3 general circulation model, aimed at documenting the simulation of North Atlantic Deep Water (NADW) and related thermohaline circulations in the Indian and Pacific Oceans. The modeled NADW is formed mainly in the Greenland– Iceland–Norwegian Seas through a composite effect of deep convection and downward cross-isopycnal transport. The modeled deep-layer outflow of NADW can reach 16 Sv near 30 °S in the South Atlantic, with the corresponding upper-layer return flow mainly coming from the “cold water path” through Drake Passage. Less than 4 Sv of the Agulhas “leakage” water contributes to the replacement of NADW along the “warm water path”. In the South Atlantic Ocean, the model shows that some intermediate isopycnal layers with potential densities ranging between 27.0 and 27.5 are the major water source that compensate the NADW return flow and enhance the Circumpolar Deep Water (CDW) flowing from the Atlantic into Indian Ocean. The modeled thermohaline circulations in the Indian and Pacific Oceans indicate that the Indian Ocean may play the major role in converting deep water into intermediate water. About 16 Sv of the CDW-originating deep water enters the Indian Ocean northward of 31 °S, of which more than 13 Sv “upwell” mainly near the continental boundaries of Africa, South Asia and Australia through inter-layer exchanges and return to the Antarctic Circumpolar Current (ACC) as intermediate-layer water. As a contrast, only 4 Sv of Pacific intermediate water is connected to “upwelling” flow southward across 31 °S while the magnitude of northward deep flow across 31 °S in the Pacific Ocean is significantly greater than that in the Indian Ocean. The model suggests that a large portion of the deep waters entering the Pacific Ocean (about 14 Sv) “upwells” continually into some upper layers through the thermocline, and becomes the source of the Indonesian throughflow. Uncertainties in these results may be related to the incomplete adjustment of the model’s isopycnal layers and the sensitivity of the Indonesian throughflow to the model’s geography and topography. Received: 12 August 1997/Accepted: 12 March 1998     

An introduction to the South China Sea throughflow: Its dynamics, variability, and application for climate

The South China Sea throughflow (SCSTF) involves the inflow through the Luzon strait and the outflow through the Karimata, Mindoro, and Taiwan straits. Recent studies have suggested that the SCSTF act as a heat and freshwater conveyor, playing a potentially important role in regulating the sea surface temperature pattern in the South China Sea and its adjoining tropical Indian and Pacific Oceans. In this introductory paper, we attempt to convey the progress that has recently been made in understanding the SCSTF. We first provide an overview of existing observations, theories, and simulations of the SCSTF. Then, we discuss its interaction with the Pacific western boundary current and Indonesian throughflow. Finally, we summarize issues and questions that remain to be addressed, with special reference to the SCSTF's dynamics, variability, and implication for climate.     

Seasonal surface ocean circulation and dynamics in the Philippine Archipelago region during 2004–2008

The dynamics of the seasonal surface circulation in the Philippine Archipelago (117°E–128°E, 0°N–14°N) are investigated using a high-resolution configuration of the Regional Ocean Modeling System (ROMS) for the period of January 2004–March 2008. Three experiments were performed to estimate the relative importance of local, remote and tidal forcing. On the annual mean, the circulation in the Sulu Sea shows inflow from the South China Sea at the Mindoro and Balabac Straits, outflow into the Sulawesi Sea at the Sibutu Passage, and cyclonic circulation in the southern basin. A strong jet with a maximum speed exceeding 100 cm s⁻¹ forms in the northeast Sulu Sea where currents from the Mindoro and Tablas Straits converge. Within the Archipelago, strong westward currents in the Bohol Sea carry the surface water of the western Pacific (WP) from the Surigao Strait into the Sulu Sea via the Dipolog Strait. In the Sibuyan Sea, currents flow westward, which carry the surface water from the WP near the San Bernardino Strait into the Sulu Sea via the Tablas Strait.These surface currents exhibit strong variations or reversals from winter to summer. The cyclonic (anticyclonic) circulation during winter (summer) in the Sulu Sea and seasonally reversing currents within the Archipelago region during the peak of the winter (summer) monsoon result mainly from local wind forcing, while remote forcing dominates the current variations at the Mindoro Strait, western Sulu Sea and Sibutu passage before the monsoons reach their peaks. The temporal variations (with the mean removed), also referred to as anomalies, of volume transports in the upper 40 m at eight major Straits are caused predominantly by remote forcing, although local forcing can be large during sometime of a year. For example, at the Mindoro Strait, the correlation between the time series of transport anomalies due to total forcing (local, remote and tides) and that due only to the remote forcing is 0.81 above 95% significance, comparing to the correlation of 0.64 between the total and local forcing. Similarly, at the Sibutu Passage, the correlation is 0.96 for total versus remote effects, comparing to 0.53 for total versus local forcing. The standard deviations of transports from the total, remote and local effects are 0.59 Sv, 0.50 Sv, and 0.36 Sv, respectively, at the Mindoro Strait; and 1.21 Sv, 1.13 Sv, and 0.59 Sv at the Sibutu Passage. Nonlinear rectification of tides reduces the mean westward transports at the Surigao, San Bernardino and Dipolog Straits, and it also has non-negligible influence on the seasonal circulation in the Sulu Sea.     

涡分辨率全球海洋环流模式LICOM模拟的吕宋海峡流场的季节变化

分析了一个1/10°的涡分辨率全球环流模式LICOM(LASG/IAP Climate system Ocean Model)对吕宋海峡附近海洋环流的模拟能力。结果表明,模拟的吕宋海峡附近上层环流及输运具有明显的季节变化特征,除6月是东向净流出外,其余月份均为西向流入,冬季流量最大。年平均流量在-3.76 Sv(1 Sv=106 m3/s),其中上层(600 m以上)流量起主要贡献,为-3.60 Sv,与目前已有的研究结果基本一致。南海通过6个海峡完成与外界的水交换,其中吕宋海峡和巴拉巴克海峡是大洋水进入南海的主要通道,其余海峡均以流出为主,流出量最大的是台湾海峡(1.99 Sv),其次是卡里玛塔海峡(1.03 Sv)。进一步分析表明,由季风引起的埃克曼输送量约占吕宋海峡流量的11%,而由季风引起的吕宋海峡压力梯度形成的西向的地转流对吕宋海峡的输运起支配作用。作为黑潮源头的太平洋北赤道流流量对吕宋海峡输运的季节变化也有一定影响。     

Validation of a regional Indonesian Seas model based on a comparison between model and INSTANT transports

The International Nusantara Stratification and Transport (INSTANT) program measured currents through multiple Indonesian Seas passages simultaneously over a three-year period (from January 2004 to December 2006). The Indonesian Seas region has presented numerous challenges for numerical modelers — the Indonesian Throughflow (ITF) must pass over shallow sills, into deep basins, and through narrow constrictions on its way from the Pacific to the Indian Ocean. As an important region in the global climate puzzle, a number of models have been used to try and best simulate this throughflow. In an attempt to validate our model, we present a comparison between the transports calculated from our model and those calculated from the INSTANT in situ measurements at five passages within the Indonesian Seas (Labani Channel, Lifamatola Passage, Lombok Strait, Ombai Strait, and Timor Passage). Our Princeton Ocean Model (POM) based regional Indonesian Seas model was originally developed to analyze the influence of bottom topography on the temperature and salinity distributions in the Indonesian seas region, to disclose the path of the South Pacific Water from the continuation of the New Guinea Coastal Current entering the region of interest up to the Lifamatola Passage, and to assess the role of the pressure head in driving the ITF and in determining its total transport. Previous studies found that this model reasonably represents the general long-term flow (seasons) through this region. The INSTANT transports were compared to the results of this regional model over multiple timescales. Overall trends are somewhat represented but changes on timescales shorter than seasonal (three months) and longer than annual were not considered in our model. Normal velocities through each passage during every season are plotted. Daily volume transports and transport-weighted temperature and salinity are plotted and seasonal averages are tabulated.     

Covariation of the Indonesian Throughflow and South China Sea Throughflow Associated with the 1976/77 Regime Shift

Changes in the Indonesian Throughflow(ITF) and the South China Sea throughflow—measured by the Luzon Strait Transport(LST)—associated with the 1976/77 regime shift are analyzed using the Island Rule theory and the Simple Ocean Data Assimilation dataset.Results show that LST increased but ITF transport decreased after 1975.Such changes were induced by variations in wind stress associated with the regime shift.The strengthening of the easterly wind anomaly east of the Luzon Strait played an important role in ...     

A diagnostic calculation of the circulation in the upper and middle layers of the Luzon Strait and the northern South China Sea during March 1992

Wind data from NCEP and hydrographic data obtained during 8–27 March 1992 have been used to compute circulation in the Luzon Strait and the northern South China Sea using three-dimensional diagnostic models with a modified inverse method. Numerical results are as follows: the main Kuroshio is located above 800 m levels. It has two intrusive branches of the Kuroshio in the areas above 400 m. One part intrudes anti-cyclonically northwestward, then flows through the area above 200 m southwest of Taiwan and into the Taiwan Strait. The other part intrudes westward and flows cyclonically in the areas north of the cyclonic eddies, then flows southward through the southern boundary of the region. The net westward volume transport (VT) through Section at 120°15′E between Luzon Island and Taiwan Island is about 3.0 Sv, net northward VT through northern boundaries into the Taiwan Strait is about 1.4 Sv and net southward VT through southern boundaries is about 1.6 Sv, which finally flows into the Karimata and Mindoro Straits. In the areas above 400 m east of 117°15′E, the circulation is mainly dominated by the basin-scale cyclonic gyre, which consists of two cyclonic eddies. However, in the areas below 400 m east of 119°00′E, the circulation is mainly dominated by basin-scale anti-cyclonic gyre. The joint effect of baroclinity and relief and interaction between wind stress and relief are important in different area respectively for the pattern of the depth-averaged flow across contours of fH⁻¹.     

Impact of the South China Sea Throughflow on the Pacific Low-Latitude Western Boundary Current: A Numerical Study for Seasonal and Interannual Time Scales

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.     

影响南海夏季风爆发年际变化的关键海区及机制初探

利用1958—2011年NCEP/ NCAR再分析资料和ERSST资料,采用Lanczos时间滤波器、相关分析、回归分析、合成分析和交叉检验等方法,研究了影响南海夏季风爆发年际变化的关键海区海温异常的来源与可能机制。结果表明,前冬(12—2月)热带西南印度洋和热带西北太平洋是影响南海夏季风爆发年际变化的关键海区。冬季热带西南印度洋(热带西北太平洋)的异常增暖是由前一年夏季El Ni?o早爆发(强印度季风异常驱动的行星尺度东-西向环流)触发、热带印度洋(西北太平洋)局地海气正反馈过程引起并维持到春季。冬季热带西北太平洋反气旋性环流(气旋性环流)及印度洋(热带西北太平洋)的暖海区局地海气相互作用使得印度洋(热带西北太平洋)海温异常维持到春末。春季,逐渐加强北移到10 °N附近的低层大气对北印度洋(热带西北太平洋)暖海温异常响应的东风急流(异常西风)及南海-热带西北太平洋维持的反气旋性环流(气旋性环流)异常,使得南海夏季风晚(早)爆发。      

Water exchange between the Bering Sea and the Pacific Ocean through the Kamchatka Strait

Hydrological and hydrochemical conditions in the Kamchatka Strait are considered, the computation of geostrophic flows is carried out, and estimations of the water exchange between the Bering Sea and the Pacific Ocean through this strait are made on the basis of the analysis of data obtained during the trip of the research vessel Miraii in August, 2004. According to the results of computations, the volume transport from the Bering Sea to the Pacific Ocean made up 10.2 Sv; mass transport, 10.4 × 10⁹ kg/s; salt transport, 0.35 × 10⁶ kg/s. The estimated value of heat transport through the strait is 11.4 × 10¹⁵ W. The Eastern Kamchatka Current carries oxygen and biogenic elements through the strait: 1222, 28, 380, and 1036 kmol/s for oxygen, phosphates, nitrates, and silicon, respectively. In total, the Bering Sea is the source of oxygen and biogenic elements for the northern part of the Pacific Ocean in the upper 500-m layer.     

Effects of tropical cyclones on large-scale circulation and ocean heat transport in the South China Sea

In this study, we investigate the influence of tropical cyclones (TCs) on large-scale circulation and ocean heat transport in the South China Sea (SCS) by using an ocean general circulation model at a 1/8° resolution during 2000–2008. The model uses a data assimilation system to assimilate observations in order to improve the representation of SCS circulation. The results reveal an unexpected deep SCS circulation anomaly induced by TCs, which suggests that effects of TC can penetrate deeper into the ocean. This deep effect may result from the near inertial oscillations excited by TCs. The inertial oscillations can propagate downward to the oceanic interior. The analyses confirm that TCs have two effects on ocean heat transport of the SCS. Firstly, the wind stress curl induced by TCs affects the structure of SCS circulation, and then changes heat transport. Secondly, TCs pump surface heat downward to the thermocline, increasing the heat injection from the atmosphere to the ocean. Two effects together amplify the outflow of the surface heat southward away the SCS through the Mindoro and Karimata Straits. The TC-induced heat transports through the Mindoro, Balabac and Karimata Straits account for 20 % of the total heat transport through three straits. An implication of this study is that ocean models need to simulate the TC effect on heat transport in order to correctly evaluate the role of the SCS through flow in regulating upper ocean circulation and climate in the Indonesian maritime continent and its adjacent regions.     

南海夏季风爆发与热带海洋海温和大气环流异常变化关系的研究

用合成和相关分析方法及SVD技术研究了南海夏季风爆发早、晚年份4～6月季风建立时期季风环流的异常及其与热带太平洋-印度洋海温的关系。结果表明,南海夏季风爆发与热带大气环流和海温变异密切相关。（1）当热带中、东太平洋—印度洋（主要在西南部）及南海海温低（高）,西太平洋—澳洲邻近海域海温高（低）时,南海夏季风爆发早（晚）。不同区域海温对季风的影响有明显的季节差异,印度洋主要为晚春至初夏（4～6月）,南海为5～6月,而热带太平洋从前冬一直持续到夏季。（2）不同的海温异常产生不同的季风环流型,南海夏季风爆发早、晚年大气环流的异常变化基本相反。南海夏季风的活动主要受印度季风环流变化的影响,与前期冬春季西太副高的强弱及位置变化密切相关。西太副高弱时,南海夏季风爆发早;反之,爆发晚。（3）热带太平洋—印度洋海温异常引起季风环流和Walker环流的异常变化可能是影响南海夏季风爆发早、晚的物理过程。     

Impacts of the MJO on Winter Rainfall and Circulation in China

Impacts of the MJO on winter rainfall and circulation in China are investigated using a real-time multivariate MJO index.Composite results using the daily rainfall anomalies and "rainy day" anomalies according to eight different MJO phases show that the MJO has considerable influence on winter rainfall in China. Rainfall anomalies show systematic and substantial changes(enhanced/suppressed) in the Yangtze River Basin and South China with the eastward propagation of the MJO convective center from the Indian Ocean to the western Pacific.When the MJO is in phase 2 and 3(MJO convective center is located over the Indian Ocean),rainfall probability is significantly enhanced.While in phase 6 and 7(MJO convective center is over the western Pacific),rainfall probability is significantly reduced. MJO in winter influences the rainfall in China mainly through modulating the circulation in the subtropics and mid-high latitudes.For the subtropics,MJO influences the northward moisture transport coming from the Bay of Bengal and the South China Sea by modulating the southern trough of the Bay of Bengal and the western Pacific subtropical high.For the mid-high latitudes,the propagation of the low frequency perturbations associated with the eastward-propagating MJO convection modulate the circulation in the mid-high latitudes,e.g.the East Asian winter monsoon and the low trough over central Asia.     

影响贵州低频强降水的主要气象因子特征

本文基于贵州低频降水和东亚水汽输送路径,对比分析低频降水多少年的水汽差异和先兆海温差异,得到主要结论有：（1）7月开始在欧亚大陆的中纬度地区开始形成“两槽一脊”的环流形势;8、9月“两槽一脊”环流形势稳固。副热带高压的西伸脊点位于120oE附近,环流形势逐渐稳定,南方地区降水有所减弱;（2）影响贵州地区水汽输送的水汽通道主要为为孟加拉湾、南海和西北太平洋,尤其是从孟加拉湾经中南半岛进入的西南风水汽输送和南半球经南海的越赤道气流;（3）低频强降水年频次多年与拉尼娜事件从准备到爆发再衰弱的不同位相期相对应,低频强降水年频次少年与厄尔尼诺事件从准备到爆发再衰弱的不同位相期相对应