西太平洋暖池热盐结构的季节变化

Using the 28°C isotherm to define the Western Pacific Warm Pool(WPWP), this study analyzes the seasonal variability of the WPWP thermohaline structure on the basis of the monthly-averaged sea temperature and salinity data from 1950 to 2011, and the dynamic and thermodynamic mechanisms based on the monthly-averaged wind,precipitation, net heat fluxes and current velocity data. A DT=–0.4°C is more suitable than other temperature criterion for determining the mixed layer(ML) and barrier layer(BL) over the WPWP using monthly-averaged temperature and salinity data. The WPWP has a particular thermohaline structure and can be vertically divided into three layers, i.e., the ML, BL, and deep layer(DL). The BL thickness(BLT) is the thickest, while the ML thickness(MLT) is the thinnest. The MLT has a similar seasonal variation to the DL thickness(DLT) and BLT.They are all thicker in spring and fall but thinner in summer. The temperatures of the ML and BL are both higher in spring and autumn but lower in winter and summer with an annual amplitude of 0.15°C, while the temperature of the DL is higher in May and lower in August. The averaged salinities at these three layers are all higher in March but lower in September, with annual ranges of 0.41–0.45. Zonal currents, i.e., the South Equatorial Current(SEC)and North Equatorial Counter Current(NECC), and winds may be the main dynamic factors driving the seasonal variability in the WPWP thermohaline structure, while precipitation and net heat fluxes are both important thermodynamic factors. Higher(lower) winds cause both the MLT and BLT to thicken(thin), a stronger(weaker)NECC induces MLT, BLT, and DLT to thin(thicken), and a stronger(weaker) SEC causes both the MLT and BLT to thicken(thin) and the DLT to thin(thicken). An increase(decrease) in the net heat fluxes causes the MLT and BLT to thicken(thin) but the DLT to thin(thicken), while a stronger(weaker) precipitation favors thinner(thicker)MLT but thicker(thinner) BLT and DLT. In addition, a stronger(weaker) NECC and SEC cause the temperature of the three layers to decrease(increase), while the seasonal variability in salinity at the ML, BL, and DL might be controlled by the subtropical cell(STC).     

赤道东印度洋和孟加拉湾障碍层厚度的年际变化及其影响机制

Interannual variability(IAV) in the barrier layer thickness(BLT) and forcing mechanisms in the eastern equatorial Indian Ocean(EEIO) and Bay of Bengal(BoB) are examined using monthly Argo data sets during 2002–2017. The BLT during November–January(NDJ) in the EEIO shows strong IAV, which is associated with the Indian Ocean dipole mode(IOD), with the IOD leading the BLT by two months. During the negative IOD phase, the westerly wind anomalies driving the downwelling Kelvin waves increase the isothermal layer depth(ILD). Moreover, the variability in the mixed layer depth(MLD) is complex. Affected by the Wyrtki jet, the MLD presents negative anomalies west of 85°E and strong positive anomalies between 85°E and 93°E. Therefore, the BLT shows positive anomalies except between 86°E and 92°E in the EEIO. Additionally, the IAV in the BLT during December–February(DJF) in the BoB is also investigated. In the eastern and northeastern BoB, the IAV in the BLT is remotely forced by equatorial zonal wind stress anomalies associated with the El Ni?o-Southern Oscillation(ENSO). In the western BoB, the regional surface wind forcing-related ENSO modulates the BLT variations.     

热带大西洋年际和年代际变率的时空结构模拟

使用美国夏威夷大学发展的中等复杂程度海洋模式(IOM)在给定表面强迫条件下模拟了热带大西洋上层海洋年际和年代际变率的时空结构.利用NCEP的41a(1958～1998年)逐月平均表面资料作为强迫场,积分海洋模式41a作为控制试验,并利用模式分别做动量(风应力)通量和热量通量无异常变化的平行试验,与控制试验作比较.对3组试验模拟上层海洋变率状况的比较,并按年际和年代际时间尺度分别分析,揭示表面风应力和热通量异常对海表面温度和温跃层深度变化的影响,并比较了其影响的相对重要性.结果表明模式成功地模拟出了热带大西洋上层海洋的变率.模式模拟的海表面温度年际变化主要表现为弱ENSO型,年代际变化表现为南、北大西洋变化相反的偶极子型.在年际时间尺度上,热力强迫和动力强迫对海表温度变化都有贡献,其中赤道外海表面温度异常(SSTA)变化主要由热通量异常引起,而近赤道SSTA的变化主要由动量异常强迫引起.在年代际时间尺度上,热通量强迫的作用远比动量强迫重要.模式不仅能够模拟SST在年际和年代际时间尺度上的变率,还能够模拟温跃层深度在年际和年代际时间尺度上的变率.年际和年代际时间尺度上,温跃层深度的变率主要由动量异常决定,热通量异常强迫的贡献很小.     

Coastal upwelling events along the southern coast of Java during the 2008 positive Indian Ocean Dipole

To understand the coastal upwelling system along the southern coast of Java, we investigated ocean temperature and salinity obtained from an Argo float. In 2008, a positive Indian Ocean Dipole (IOD) event began to develop in early May and anomalously cool SST developed around south of Java from May to September. During the peak of the IOD, an Argo float successfully observed vertical structure of temperature and salinity within 90 km from Java. The float observed two intraseasonal-scale temperature cooling events in July and August, with significant upward movements of the thermocline more than 90 m. Concurrent with the signals, anomalous southeasterly alongshore winds, lowering of local SST and sea level, and upward expansion of high-salinity water were also observed. During the event in August, vertical velocity estimated by the anomalous wind stress agreed well with the observations. These results indicate that the Argo float observed the coastal upwelling, which was enhanced by the 2008 positive IOD, along the southern coast of Java.     

孟加拉湾上层地转环流周年变化的遥感研究

应用1993～2003年TOPEX/Poseidon卫星测高数据结合历史水文资料,反演了孟加拉湾海面动力地形的平均周年变化,探讨了孟加拉湾上层环流季节特征和演变规律.结果显示,虽然孟加拉湾的大气环流受季风支配年周期波动显著,但表层环流形态的周年演变却呈3个不同的阶段.1～4月间(东北季风后期)湾内受一个海盆尺度的强大反气旋式环流的支配,湾口为西向流;5月西南季风骤起,印度季风漂流越过印度半岛南端出现在湾口,湾内反气旋环流弱化,在其南北两侧各出现一气旋式涡,构成5～9月间南北相间的三涡结构;10月东北季风再起,湾口漂流再次转向,10～12月间湾内则为海盆尺度的弱气旋式环流.受上述环流格局影响,位于西边界的印度沿岸流亦呈相应的3个阶段变化.分析表明,孟加拉湾风应力旋度的变化是造成湾内环流3个阶段演变的主要原因.本地风场和来自赤道海域的外强迫的共同驱动形成了孟加拉湾环流周年演变的独特规律.     

Mesoscale wind stress–SST coupling in the Kuroshio extension and its effect on the ocean

Mesoscale perturbations (with a size of 100–1000 km) of wind stress magnitude, divergence and curl in the Kuroshio Extension (KE) are observed to tightly link to those of sea surface temperature (SST), and downwind and crosswind SST gradients, respectively. Based on long-term satellite observational data, their empirical relationships are established, which are further used to represent mesoscale wind stress–SST coupling in an ocean model that is based on the Regional Oceanic Modelling Systems (ROMS). The strength of mesoscale perturbations of wind stress and SST is observed to display a consistent seasonal variability, with the maximum appeared in winter while the minimum appeared in summer. This seasonal variability characteristic is also successfully simulated by ROMS with high resolution. Through comparing two experiments with and without the mesoscale wind stress–SST coupling, it is found that the mesoscale wind stress perturbation (τ _MS) has a negative feedback on SST perturbation (SST_MS). Analyses of sensitivity experiments suggest that the τ _MS acts to inhibit SST_MS mainly by means of surface heat flux. The τ _MS –SST_MS coupling also exerts influences on the ocean mean state and seasonal variability of SST in the KE. The effect of τ _MS on the SST is distinct in autumn and winter when the mesoscale perturbations are most active. Analyses of sensitivity experiments demonstrate that the τ _MS can affect the long term mean SST through either way of surface heat flux or momentum flux.     

赤道东印度洋和孟加拉湾障碍层厚度的季节内和准半年变化

利用2002—2015年ARGO网格化的温度、盐度数据, 结合卫星资料揭示了赤道东印度洋和孟加拉湾障碍层厚度的季节内和准半年变化特征, 探讨了其变化机制。结果表明, 障碍层厚度变化的两个高值区域出现在赤道东印度洋和孟加拉湾北部。在赤道区域, 障碍层同时受到等温层和混合层变化的影响, 5—7月和11—1月受西风驱动, Wyrtki急流携带阿拉伯海的高盐水与表层的淡水形成盐度层结, 同时西风驱动的下沉Kelvin波加深了等温层, 混合层与等温层分离, 障碍层形成。在湾内, 充沛的降雨和径流带来的大量淡水产生很强的盐度层结, 混合层全年都非常浅, 障碍层季节内变化和准半年变化主要受等温层深度变化的影响。上述两个区域障碍层变化存在关联, 季节内和准半年周期的赤道纬向风驱动的波动过程是它们存在联系的根本原因。赤道东印度洋地区的西风(东风)强迫出向东传的下沉(上升)的Kelvin波, 在苏门答腊岛西岸转变为沿岸Kelvin波向北传到孟加拉湾的东边界和北边界, 并且在缅甸的伊洛瓦底江三角洲顶部(95°E, 16°N)激发出向西的Rossby波, 造成湾内等温层深度的正(负)异常, 波动传播的速度决定了湾内的变化过程滞后于赤道区域1~2个月。     

南海表层水温年际变化的大尺度特征

通过对COADS海洋气象资料的分析,得出南海表层水温(SST)年际变化的若干大尺度特征.结果表明:南海SST年际具有一定的准周期性,其显著周期为24～30个月;南海SST年际变化与年循环之间有着一种锁相关系,关键位相在于北半球冬春季节;南海典型冷暖年份合成SST距平场的时空结构十分相似;在年际时间尺度上,南海SST和南方涛动指数有反相关系,与经向风海面热收支之间有同位相关系;南海暖池面积指数的年际变化与南海SST年际变化一致.     

Seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean based on WHOI flux product

The mean seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean is examined using the Woods Hole Oceanographic Institution(WHOI) flux product.The most turbulent heat fluxes occur during winter seasons in the two hemispheres,whose centers are located at 10°~20°N and 5°～15°S respectively.In climatological ITCZ,the turbulent heat fluxes are the greatest from June to August,and in equatorial cold tongue the turbulent heat fluxes are the greatest from March to May.Seasonal variability of sensible heat flux is smaller than that of latent heat flux and mainly is dominated by the variations of air-sea temperature difference.In the region with larger climatological mean wind speed(air-sea humidity difference),the variations of air-sea humidity difference(wind speed) dominate the variability of latent heat flux.The characteristics of turbulent heat flux yielded from theory analysis and WHOI dataset is consistent in physics which turns out that WHOI's flux data are pretty reliable in the tropical Atlantic Ocean.     

Coupled seasonal variability in the South China Sea

The present study documents the relationship between seasonal variations in sea surface temperature (SST) and precipitation in the South China Sea (SCS) region. There are strong interactions between the atmosphere and ocean in the seasonal variations of SST and precipitation. During the transition to warm and cold seasons, the SST tendency is primarily contributed by net heat flux dominated by shortwave radiation and latent heat flux with a complementary contribution from ocean advection and upwelling. The contribution of wind-driven oceanic processes depends on the region and is more important in the northern SCS than in the southern SCS. During warm and cold seasons, local SST forcing contributes to regional precipitation by modulating the atmospheric stability and lower-level moisture convergence. The SST difference between the SCS and the western North Pacific influences the convection over the SCS through its modulation of the circulation pattern.     

北部湾温度锋的季节与年际变化

采用8a(1991—1998)的卫星遥感海水表面温度资料(AVHRR SST)对北部湾温度锋的季节变化与年际变化规律进行了探讨。北部湾海区温度锋的季节态强弱趋势为春季最强，夏季、冬季次之，秋季最弱。在年际时间尺度上，温度锋强度与SST距平(SSTA)存在响应关系，表现在：1)SST正距平对应较弱的锋面产生，负距平对应较强的锋面产生，这种相关性在冬季表现得最为明显；2)锋面的强弱与SSTA绝对值存在正相关关系，即SSTA变化越大，锋面越强。在冬季，温度锋强度与海面风经向分量相关，在偏北风异常情况下，锋面较强；反之，锋面较弱。     

海面温度变化影响台风"海棠"强度的数值研究

通过对台风"海棠"5 d的数值模拟,研究海表温度(SST)变化对台风强度的影响。与NCEP月平均海表温度相对比,在中尺度大气模式中引入热带测雨卫星(TRMM)微波成像仪(TMI)/先进微波扫描辐射计(AMSR-E)来考察SST对台风"海棠"路径和强度的影响。研究结果表明,每天变化SST的试验模拟的台风强度和路径整体效果不错;模拟的台风路径不敏感于SST的变化,而台风强度的变化不仅取决于由于台风移动引发的SST冷却的幅度大小,而且取决于SST冷却区域的相对位置。在台风"海棠"强烈发展过程中,台风中心右侧冷却区对台风中心气压影响很小;台风强烈发展过后,SST冷却区开始影响台风强度,但造成台风中心气压下降幅度不大,6 h内台风中心气压减弱约3.9 hPa。海面热量通量和海面风速与SST的分布都有良好的相关性:在SST变化为正值的暖水区,感热通量和潜热通量都是一个正的通量分布的极值区,并有风速极大值区域存在;在台风右侧相应的冷却区,则存在着负的通量异常和风速极小值区域。     

Annual cycle of stratification and tidal fronts in the Bohai Sea: A model study

In general, competition between buoyancy mechanisms and mixing dynamics largely determines the water column structure in a shelf sea. A three dimensional baroclinic ocean model forced by surface heat fluxes and the 2.5 order Mellor-Yamada turbulence scheme is used to simulate the annual cycle of the temperature in the Bohai Sea. The difference between the sea surface temperature (SST) and sea bottom temperature (SBT) is used to examine the evolution of its vertical stratification. It is found that the water column is well-mixed from October to March and that the seasonal thermocline appears in April, peaks in July and then weakens afterwards, closely following the heat budget. In addition, the Loder parameter based on the topography and tidal current amplitude is also computed in order to examine tidal fronts in the BS, which are evident in summer months when the wind stirring mechanism is weak.     

印度洋波浪诱导的水体输运效应及其对赤道SST异常的影响

波浪诱导的水体输运会对海洋产生大尺度影响。结合波浪大尺度效应的研究现状和印度洋涌浪分布的事实,利用ECMWF-CERA20的波浪、海表面温度(SST)及风场数据,采用多种统计分析方法,研究了波浪输运与赤道印度洋SST的潜在关系。结果显示:中高纬度波浪输运异常的低频信号在空间、周期上与赤道SST异常均有高度相似性;Stokes漂流纬向、经向异常呈现出南—北、东—西的振荡,其第二模态时间序列与印度洋偶极子(Indian Ocean Dipole,IOD)指数存在强相关性并在La Ni a次年的负IOD事件中达到最高:相关系数在ACC区域纬向异常超前6个月时接近0.6,中纬度区域经向异常在超前3个月时达到0.7。在La Ni a次年的负IOD中,波浪经向输运异常的相位(超前三个月)与赤道SST异常相位呈全年反相位,经向浪致输运异常造成的东—西热量输运差异对赤道SST异常分布有不可忽略的贡献。     

孟加拉湾障碍层年际变化及其与印度洋偶极子事件的联系

利用1980-2015年SODA温盐资料,结合Argo数据分析了印度洋偶极子(IOD)事件年份孟加拉湾障碍层的变化特征及其形成机制。结果表明,IOD事件年份孟加拉湾障碍层变化显著。纯的正IOD(纯pIOD)年份及伴随型pIOD年份盛期(9-11月),除孟加拉湾内西南海域障碍层厚度略变厚约5 m外,赤道海域、安达曼海至孟加拉湾北部障碍层厚度均变薄5～15 m,此障碍层距平盛期形态在纯pIOD年份随pIOD消亡迅速消退,但在伴随型pIOD年份维持至翌年3-5月才开始弱化。纯的负IOD(纯nIOD)年份障碍层厚度变化特征与pIOD年份大体相反。进一步分析表明,IOD事件年份赤道风场距平的远地强迫造成等温层深度的变化是湾内障碍层变化的主因。在伴随型IOD年份,受ENSO事件的影响,赤道风场距平在IOD消亡后仍得以维持3个月以上,使得湾内障碍层距平形态持续更久。除赤道远地强迫外,湾内局地风场的Ekman抽吸作用以及混合盐度变化对障碍层厚度年际变化也有一定影响。     

Equatorial influence of QuikSCAT winds in an isopycnal ocean model compared to NCEP2 winds

An ocean model was used to examine whether the scatterometer winds can improve the model performance both dynamically and thermodynamically. Comparisons were done using QuikSCAT and NCEP2 winds for both the mean and variability from 2000 to 2004. The comparisons showed that the model forced by QuikSCAT winds gives more realistic mean SST, 20 °C isotherm depth (Z20), and latent heat flux than NCEP2 winds do. Sensitivity experiments indicated that QuikSCAT mean wind stress is important for the improved mean SST, Z20, and latent heat release to the atmosphere in the eastern Pacific. QuikSCAT wind speed, through its effect on the turbulent heat fluxes, is most important for the mean SST in the western Pacific. Finally, there were comparable correlations with observations of both SST and Z20 on the intra-seasonal time scale between the model forced with QuikSCAT winds and the model forced with NCEP2 winds.     

基于浮标、NCEP2及OAFlux产品的新海表感热和潜热通量对比分析

New satellite-derived latent and sensible heat fluxes are performed by using Wind Sat wind speed, Wind Sat sea surface temperature, the European Centre for Medium-range Weather Forecasting(ECMWF) air humidity, and ECMWF air temperature from 2004 to 2014. The 55 moored buoys are used to validate them by using the 30 min and 25 km collocation window. Furthermore, the objectively analyzed air-sea heat fluxes(OAFlux) products and the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis 2(NCEP2) products are also used for global comparisons. The mean biases of sensible and latent heat fluxes between Wind Sat flux results and buoy flux data are –0.39 and –8.09 W/m~2, respectively. In addition, the rootmean-square(RMS) errors of the sensible and latent heat fluxes between them are 5.53 and 24.69 W/m~2,respectively. The RMS errors of sensible and latent heat fluxes are observed to gradually increase with an increasing buoy wind speed. The difference shows different characteristics with an increasing sea surface temperature, air humidity, and air temperature. The zonal average latent fluxes have some high regions which are mainly located in the trade wind zones where strong winds carry dry air in January, and the maximum value centers are found in the eastern waters of Japan and on the US east coast. Overall, the seasonal variability is pronounced in the Indian Ocean, the Pacific Ocean, and the Atlantic Ocean. The three sensible and latent heat fluxes have similar latitudinal dependencies; however, some differences are found in some local regions.     

吕宋海峡西部深海盆内孤立波潜标观测研究

Using a net surface heat flux （Qnet） product obtained from the objectively analyzed air-sea fluxes （OAFlux） project and the international satellite cloud climatology project （ISCCP）, and temperature from the simple ocean data assimilation （SODA）, the seasonal variations of the air-sea heat fluxes in the northwestern Pa cific marginal seas （NPMS） and their roles in sea surface temperature （SST） seasonality are studied. The seasonal variations of Qnet, which is generally determined by the seasonal cycle of latent heat flux （LH）, are in response to the advection-induced changes of SST over the Kuroshio and its extension. Two dynamic regimes are identified in the NPMS： one is the area along the Kuroshio and its extension, and the other is the area outside the Kuroshio. The oceanic thermal advection dominates the variations of SST and hence the sea-air humidity plays a primary role and explains the maximum heat losing along the Kuroshio. The heat transported by the Kuroshio leads to a longer period of heat losing over the Kuroshio and its Extension. Positive anomaly of heat content corresponds with the maximum heat loss along the Kuroshio. The oceanic advection controls the variations of heat content and hence the surface heat flux. This study will help us understand the mechanism controlling variations of the coupled ocean-atmosphere system in the NPMS. In the Kuroshio region, the ocean current controls the ocean temperature along the main stream of the Ku roshio, and at the same time, forces the air-sea fluxes.     

Multidecadal climate variability in the subtropics/mid‐latitudes of the Southern Hemisphere oceans

Observations of multidecadal variability in sea surface temperature (SST), surface air temperature and winds over the Southern Hemisphere are presented and an ocean general circulation model applied towards investigating links between the SST variability and that of the overlying atmosphere. The results suggest that the dynamical effect of the wind stress anomalies is significant mainly in the neighbourhood of the western boundary currents and their outflows across the mid‐latitudes of each Southern Hemisphere basin (more so in the South Indian and South Atlantic than in the South Pacific Ocean) and in the equatorial upwelling zones. Over most of the subtropics to mid‐latitudes of the Southern Hemisphere oceans, changes in net surface heat flux (particularly in latent heat) appear to be more important for the SST variability than dynamical effects. Implications of these results for modelling and understanding low frequency climate variability in the Southern Hemisphere as well as possible links with mechanisms of decadal/interdecadal variability in the Northern Hemisphere are discussed.     

Meteorological forcing of long-term temperature variations of the Dutch coastal waters

Time series of observations of the sea surface temperature (SST) at 12 stations in the Dutch coastal zone are analyzed to establish whether an earlier published nearly 150 year long SST time series from the Marsdiep tidal inlet is representative for the whole Dutch coastal zone. The annual cycles (SST range and phase) as well as the long-term SST trends at decadal scales from other estuaries agree with the Marsdiep time series. An increasing SST trend since 1982 is a phenomenon of the whole Dutch coastal zone. In order to increase the understanding of the causes of the observed SST variability, a multiple linear regression model is constructed, which links locally determined seasonal meteorological and oceanographic forcing factors to the seasonal mean SST. The oceanographic forcing factor is the SST value from the preceding season, representing persistence due to thermal inertia of the sea. Season to season changes of the atmospheric circulation, connected with SST variability, are represented by seasonal mean wind components as forcing factors, e.g. the western winds in winter which bring relatively warm air masses to Western Europe. For the seasons where shortwave solar radiation is the dominant term in the local heat budget (spring and summer), the number of bright sun hours is used as forcing factor, roughly representing the effects of changing cloudiness. The annual mean SST, derived from the regression models for the four seasons, applied to 4 locations along the Dutch coast, correlates quite well, not only for the year to year variability (R = 0.88) but also for the longer-term SST trends (R = 0.95). An explicit local greenhouse effect is not required as separate forcing factor to explain the recent warming trend of Dutch coastal waters starting in the early 1980s; coincident variations in wind statistics and cloudiness are a sufficient explanation.