中国近50年寒潮冷空气的时空特征及其与北极海冰的关系

利用中国具有较长时间序列的527个站点1961—2010年的日平均温度观测资料,美国国家环境预报中心和国家大气研究中心(NCEP/NCAR)再分析资料以及伊利莱诺斯大学的海冰密集度资料,分析了我国近50年来寒潮的时空变化及与其相联系的海冰和大气环流异常的关系。结果表明,中国寒潮冷空气活动频数存在两个主要模态,第一模态表现在中国北方冷空气活动频数呈年代际减少趋势,1980年之前寒潮冷空气频数偏多,1990年后寒潮冷空气频数偏少;第二模态表现为我国南方冷空气频数的年际振荡特征。第一模态寒潮冷空气频数的减少主要与全球变暖有关,北极海冰的减少使得1980年代后期北极涛动加强,并激发出欧亚遥相关波列进而影响我国的寒潮冷空气活动。第二模态则与近些年来夏季北极海冰的快速融化以及北极大气出现偶极子型环流异常有关,通过激发跨极型和类欧亚遥相关波列影响到后冬的中国南方寒潮冷空气活动增多。     

东亚冬季气温的年际变化特征及其与海温和海冰异常的关系

通过谐波分析的方法,对东亚31个冬季(1980—2010年)的气温提取年际变化分量(周期小于8a部分)进行EOF分析。结果发现:在年际变化的时间尺度上,东亚冬季气温表现为高纬模态和低纬模态2个主要模态,它们一起可以解释总方差73%的变化。进一步分析表明,在年际变化尺度上,与气温变化的高纬模态相联系的大气环流表现为显著的北极涛动(AO)负位相分布,海平面气压场上西伯利亚高压和阿留申低压北移,对流层中层东亚大槽西移,高层西风急流向西北方向移动;副热带北太平洋和阿拉斯加湾的海表面温度(SST)变化呈偶极子振荡分布,这种准两年的周期振荡对这一模态的出现有一定的预示意义。而与气温变化的低纬模态相联系的大气环流表现为类AO正位相分布,与之相关的西伯利亚高压和阿留申低压南移,对流层中层东亚大槽东移,高层的西风急流则是向东南方向移动;赤道东太平洋的SST异常可能对这一模态的形成有一定的作用,而东亚近海的SST则更多是被动地改变。此外,海冰异常变化与东亚冬季气温变化的联系主要体现在:在前夏和前秋,东西伯利亚海-波弗特海海冰异常减少(增加)对应着随后东亚冬季气温变化的高纬模态(低纬模态),而冬季东亚气温变化的高纬模态(低纬模态)又与后期春季北极东半球的海冰异常增加(减少)具有较好的相关性,此外白令海和鄂霍次克海的海冰异常变化是伴随东亚冬季气温变化产生的。     

北太平洋热带的低频振荡——北方涛动

北方涛动是近几年在北太平洋热带地区发现的一种东西向的大气涛动.本文试图对北方涛动的空间结构和时间变化(包括季节变化和年际变化)的基本特征及其与热带太平洋海温、降水、信风和沃克环流等的联系作进一步的分析研究.经验正交函数(EOF)分析的结果,不仅进一步证实了北方涛动存在的真实性,而且还揭示了它的大尺度特征及其在北太平洋大气环流年际变化中占有头等重要的地位.据延伸的1921-1946年资料的分析表明,北方涛动仍然非常明显,说明它不是某一时期特有的现象,而是北太平洋热带地区大气环流固有的一种低频振荡.北方涛动3-4年的年际振荡与热带太平洋海温、降水、信风和沃克环流关系密切.并且它在这一频带与南方涛动发生强烈的耦合.我们认为,东赤道太平洋之所以是全球热带海洋中海温年际变化最大的地区,以及该区的海气相互作用之所以能够产生世界性年际气候变化最强的信号,可能与它们之间强烈的耦合作用不会没有关系.     

北极超强气旋活动及其大气环流特征

北极极端气旋过程能够反映北极气候变化特征并对北极水文气象要素的调节具有重要影响,其活动及大气环流形势特征值得关注。利用美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)与美国国家大气研究中心(National Center for Atmospheric Research,NCAR)提供的逐日再分析资料定义北极超强气旋(Arctic Super Cyclone, ASC)过程,结合美国国家冰雪数据中心(National Snow and Ice Data Center, NSIDC)基于NCEP/NCAR再分析资料追踪识别的北半球气旋及特征资料,分析了ASC的活动特征及其大气环流特征。结果表明:判别ASC的北极最低气压5%阈值具有显著的冬季低夏季高的单峰型季节变化特征,冬季ASC的强度远强于夏季;ASC多从大西洋扇区经北欧海?巴伦支海?喀拉海输入到极区,也存在少部分极区原生或太平洋扇区输入;ASC多生成于两大洋急流轴或急流出口区北侧,极少数生成于大陆或中低纬度,且绝大多数在极区消亡难以回到中纬度。极区原生ASC频数占总数约1/3,整体没有显著增减趋势,但长生命史ASC频数以0.49次/(10 a)的趋势增多,表明其持续时间增长。ASC频数与北极涛动(Arctic Oscillation, AO)在冬季相关性很好,其大气环流形势回归场中极区海平面出现低压低温异常,高空极涡加深且两大洋急流偏北,中纬度急流主轴偏弱;ASC的生成发展不仅有利于AO向正位相转变,同时AO正位相下也有利于ASC活动的增强,ASC活动是AO位相变化的潜在指标。     

北半球中高纬度大气环流主模态的季节演变及其与北极海冰变化的联系

利用31a(1979—2009)气候月平均的海平面气压(SLP)资料,提出1种与北半球中高纬度环流转变相适应的分季法。并根据这个客观分季方法,通过SEOF分析,发现大气环流主模态的季节演变有着典型的北极涛动(AO)空间结构,其时间系数在1990年代中期发生转型。500hPa上纬向波的涡度有着南北反位相的分布特征,冬季正涡度的区域对应着气旋性环流,其覆盖范围广,而夏季正涡度区域更偏北,可见AO在冬季增强,夏季减弱。北半球SLP异常的EOF分解第一模态为北极涛动(AO),第二模态是偶极异常(DA);将这2个模态称之为北半球中高纬度大气环流异常的优势模态。通过计算优势模态与海冰面积的超前滞后相关性,发现AO依然是控制海冰变化的前期大气环流异常的模态,而DA则可能是海冰快速变化后期大气环流的主导模态。     

秋季西北太平洋热带气旋累积能量的年际变化及其预报

秋季是西北太平洋热带气旋平均强度最强的季节,热带气旋累积能量(accumulated cyclone energy,ACE)是热带气旋平均强度的表征指标,基于1979—2015年日本气象厅最佳路径热带气旋数据集,以及美国冰雪中心海冰数据和哈得来环流中心海温数据,利用回归分析和多元逐步回归等方法,对秋季西北太平洋ACE指数进行了分析和预报。研究表明:秋季西北太平洋ACE指数具有显著的年际变化特征,与厄尔尼诺-南方涛动(ENSO)有关,最大和最小值分别出现在1991年的厄尔尼诺年和1999年的拉尼娜年,在厄尔尼诺发展年的秋季ACE一般较强,而在拉尼娜衰减年的秋季热带气旋强度则较弱; ACE指数变化受来自北极海冰变化强迫中纬度异常波列的影响及其受到厄尔尼诺海温模态的调制;由于海冰在波弗特海的异常增多,强迫对流层高层夏季出现类似北半球环球遥相关型异常波列,波列正压下传,使得夏秋季西北太平洋副热带高压东退北移;副热带高压活动的变化和太平洋海温的异常分布影响了局地的环流,热带气旋生成源地弱的垂直风切变区域偏东和涡度显著增大有利于热带气旋在暖海洋上发展强盛。最后进行建模预报,预报效果为0.69。若单独使用海温或海冰作为唯一要素来预报,预报效果将大大降低。     

长江流域夏季极端高温的年代际变化特征及其与大西洋多年代际振荡的关系

本文基于地面观测资料和NCEP/NCAR再分析数据,利用经验正交函数分析、线性回归分析等方法对1960—2016年夏季(6—8月)长江流域的极端高温(Extreme High Temperature,EHT)事件的强度、暖昼、暖夜发生日数的年代际特征及其对应大气环流进行分析,并探讨了EHT事件与大西洋多年代际振荡(Atlantic Multidecadal Oscillation,AMO)的关系。结果表明,中国夏季长江流域的极端高温事件存在明显的年代际变化特征,其中1960—1970年和2002—2016年为暖时期,1971—2001年为冷时期。相较于冷时期,暖时期在高温强度、暖昼和暖夜的发生日数方面均明显偏暖。针对于该极端高温年代际特征的成因,研究结果表明,暖时期位于长江流域北部的对流层中高层异常反气旋和偏北偏西的西太平洋副高有利于该地区下沉运动的增强,进而有利于极端高温的出现。同时,在对流层低层,位于中国东部的异常反气旋将低纬地区的暖湿气流携带至长江流域,这也有利于长江流域EHT事件的发生。此外,进一步分析表明,AMO与长江流域夏季EHT事件在年代际尺度上存在明显的关系,AMO超前中国夏季长江流域的EHT事件6~8 a,这对预测中国长江流域极端高温事件具有一定的指示作用。     

南方涛动年际变化的周期

一、前言自从半个世纪前沃克发现并命名了“南方涛动”(SO)以来,许多气象学家和海洋学家相继对南方涛动现象进行了大量研究。到60年代后期,许多学者又把它与厄尔尼诺(ElNino)现象联系起来,统称为厄尔尼诺/南方涛动(ENSO)现象。已有的研究结果表明:南方涛动远远不是仅仅涉及到东南太平洋上的高压带与北澳大利亚到印度尼西亚低压带间海平面气压波动,它已被看成是全球尺度的年际气候变化的一个最突出的标志,并且它和热带海平面的气压变化、季风降雨及北美和热带以外的其他地区的冬季环流变化有关。此外,还有的研究把它与印度的干旱、北半球的大气平均温度、渔业捕获量和农业     

中国近海海表温度变化的极端特性及其气候特征研究

本文基于1982–2017年日再分析数据,分析了中国近海海表温度变化的极端特性、历史演变、空间格局及可能影响,并探讨了与全球变化和区域气候变率的关联性。近30多年来,中国近海海表总体升温明显,尤以春季长江口附近及以南的外部近岸海域升温最为显著,线性升温速率高达0.2°C/(10 a)。相比而言,沿岸海域对气候变暖暂缓的响应可能更为明显;极端高(低)温强度以显著增强(减弱)为主,尤以春(夏)季幅度最大。沿岸海域春季极值温差增强显著,易通过物候变化引起生物迁移和赤潮等生态灾害突发、频发;北部海域极端事件持续天数大于南部,其中,黄海、东海极端高温持续天数增加显著,可能对渔业资源产生较大影响。受气候变暖暂缓影响,极端低温持续天数亦显著增加;极端高温在长江口附近,台湾海峡和南海北部等海域累积频次上升显著,未来极端海洋热浪事件可能持续增加,将对南海珊瑚礁等产生较大影响。极端低温累积频次以显著降低为主。然而长江口及以南沿岸极端低温在冬春季增强明显,可能对红树林等产生一定影响;太平洋年代际振荡(PDO)暖位相期间,ENSO暖事件得到增强,易引起中国近海海表极端低温的频发。北极涛动(AO)正位相时,限制了极区冷空气向南扩展,中国近海海表极端高温频次趋于增加,其危险性增强。     

三沙市海域海平面变化

使用1993-2011年的台站和卫星高度计资料详细分析了三沙市海域近19 a的海平面变化特征及规律。结果表明:三沙市周边海域海平面存在明显的季节变化,且区域特征明显。海平面变化除了明显的年和半年周期,2~3 a、4~7 a和准9 a的周期也较显著。海平面长期变化呈现明显的波动上升趋势,且空间分布上区域特征显著,西沙群岛南部海域海平面上升趋势最强,西沙群岛北部与中沙群岛西部次之,南沙群岛东部海平面上升速率较快,南沙群岛西部上升趋势最弱。受大气环流等异常气候事件的影响,1998年和2010年海平面的年际变化波动较大,年变化振幅显著偏高。未来三沙市海平面将继续上升,预计2030年、2050年、2070年和2100年海平面将比常年分别升高约11 cm、20 cm、30 cm和45 cm。     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance.     

A Review of Some Environmental Issues Affecting Marine Mining

This article reviews information recently available from existing marine and coastal mining for responses to environmental issues affecting marine mining at different depths. It is particularly but not exclusively concerned with those issues affecting seabed biodiversity impact and recovery. Much information has been gathered in the past 10 years from shallow mining operations for construction aggregate, diamonds, and gold, from coastal mines discharging tailings to shallow and deep water, and from experimental deep mining tests. The responses to issues identified are summarized in a series of eight tables intended to facilitate site-specific consideration. Since impacts can spread widely in the surface mixing layer SML, and can affect the biologically productive euphotic zone, the main issues considered arise from the depth of mining relative to the SML of the sea. Where mining is below the SML, the issue is whether it is environmentally better to bring the extraction products to the surface vessel for processing (and waste discharge), or to process the extraction products as much as possible on the seabed. Responses to the issues need to be sitespecific, and dependent on adequate preoperational environmental impact and recovery prediction. For deep tailings disposal from a surface vessel, there are four important environmental unknowns: (1) the possible growth of "marine snow" (bacterial flocs) utilizing the enormous quantities of fine tailings particles (hundreds or thousands of metric tons per day) as nuclei for growth, (2) the possibility that local keystone plankton and nekton species may migrate diurnally down to and beyond the depth of deep discharge and hence be subjected to tailings impact at depth, (3) the burrow-up capability of deep benthos and their ability to survive high rates of tailings deposition, and (4) the pattern and rate of dispersion of a tailings density current through the deep water column from discharge point to seabed. Actions to obtain relevant information in general and site-specifically are suggested.     

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement.     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

Determination of In Situ Sediment Shear Strength from Advanced Piston Corer Pullout Forces

The advanced piston corer (APC) has been used by the Ocean Drilling Program since 1985 for recovering soft sediments from the ocean floor. The pullout force measured on extracting the core barrel from the sediment is shown to correlate with the average shear strength of the sediment core measured in the ship's laboratory. A simple rule of thumb is derived relating the shear strength of the sediment to the pullout force. Multiple APC holes at individual sites allow the consistency of the pullout measurements to be assessed. The effects of different operational procedures during APC coring are also explored. Although generally applicable, the correlation between pullout force and laboratory measurements of shear strength breaks down for some APC holes, possibly because of the disturbance of some sediment types during the APC coring process. A better understanding of the physical process of APC coring, and its effect on the properties of the sediment both inside and immediately outside the core barrel, would indicate what confidence can be put on the measurement of pullout force as a way of evaluating the in situ shear strength of deep sea sediments.     

《Acta Oceanologica Sinica》Vol. 33(2014) contents

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INFORMATION FOR AUTHORS

<正>Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.The journal publishes scholarly papers on marine science and technology,including physics,chemistry,biology,