西北太平洋海面高度异常对热带气旋的响应

采用一种海面高度异常(Sea Level Anomaly,SLA)对热带气旋响应的合成分析方法,即根据热带气旋的路径位置和运动方向对海面高度异常进行插值、旋转和平均,得到不同热带气旋强度下,以热带气旋最佳路径点为原点的海面高度异常场.利用该方法,基于Aviso卫星高度计数据和中国气象局热带气旋最佳路径数据,得到了199...     

热带太平洋海面高度年代际变化的研究

采用SODA海面高度(SSH)数据研究热带太平洋海域的年代际变化.结果表明,热带太平洋海面高度场存在与太平洋年代际涛动(PDO)时间过程基本一致的年代际变化,但是SSH异常的空间分布与SST异常的是不同的.热带海域年代际变化的典型空间分布:海面高度异常在热带海域存在东西方向的反向变化,在西太平洋只有1个变化中心,而在东太平洋形成2个对称于赤道的变化中心.热带太平洋海面高度的年代际变化有2个基本周期:13 a左右的周期和30 a以上时间尺度的气候转型周期.其中13 a周期的年代际变化与ENSO年际过程无关,是热带太平洋年代际变化的重要组成部分.由于数据时间长度的限制,气候转型的时间尺度还不明确,也不清楚其是否有明显的周期性.比较热带东西太平洋年代际变化的特征,可以发现以气候转型期的年代际信号在东西太平洋几乎是同时发生的,而13 a左右周期的年代际信号在赤道附近却存在自西向东方向的传播.     

热带太平洋冬季海面气象特征分析

本文主要根据1985—1986年冬季热带太平洋大面积海洋气象调查资料,初步分析了热带太平洋中、西部海区海面气象要素基本特征。指出热带太平洋海面气象要素随经度而变化的规律性是比较明显的。一般是以170°E为界,其东、西两侧变化趋势基本相反,离开赤道越远,要素的经向变化越显著,在赤道上要素的经向变化最小。并指出北太平洋副热带高压及西太平洋赤道辐合带是形成上述规律的主要原因。     

热带太平洋-南海-印度洋海面风与海面温度年际变化整体耦合的主模态

利用COADS资料和相关分析、经验正交函数分解、奇异值分解和小波分析等方法对热带太平洋-南海-印度洋的海表面温度(SST)及海面风场(SSW)进行了研究,确定了热带太平洋、南海以及印度洋作为1个整体时海面风场及海面温度场相互作用的主模态。在把热带太平洋、南海和印度洋作为整体的情况下,研究了该模态的时空分布特征。各种方法研究均表明,该模态在热带太平洋上为ENSO模态;在热带印度洋上为对应于ENSO态的印度洋“单极型”模态;在南海则表现为整个海盆尺度上的一致型。     

热带太平洋要素场与ENSO的非线性相关特征分析

为进一步揭示热带太平洋海气系统要素场之间的非线性相关特征,基于Hadley提供的海温场资料和美国国家环境预报中心(NCEP)和美国国家大气研究中心(NCAR)提供的海面风场和海面气压场资料,采用经验正交(EOF)分解和非线性典型相关分析法(NLCCA),分析了海温、海面风场和海面气压场三要素场之间的非线性相关性。结果表明,西太平洋暖池的异常暖状态和热带太平洋的西风异常与ENSO的非线性之间存在着密切关联。进一步引入奇异值分解方法(SVD),将其与NLCCA方法相结合,分析了热带太平洋海温场与海面风场、海面气压场耦合变化的关键影响区及其异性相关的分布特征。分析表明,热带太平洋西风异常和西太副高与ENSO循环之间存在较好的相关性。具体表现在:海温在中东太平洋地区出现异常增暖时,有助于加强东南亚地区的对流发展,促使东南亚地区季风的提前爆发;而东北太平洋副热带高压强度变化对北太平洋中部Nam ias海区海温距平的东西向振荡具有重要作用。研究为ENSO循环的非线性特性提供了有力的证明,也为ENSO的预测研究奠定了相关基础。     

散射计海面风场资料在远洋航天气象保障中应用方向探讨

结合目前远洋航天气象保障中关注重点及存在的弱点,创新尝试引入高精度散射计海面风场资料,探讨散射计海面风场资料在远洋航天气象保障中应用的可行方向,主要包括应用于诊断海面风场气候统计特征、应用于诊断热带气旋生成预报预警、应用于诊断热带气旋内部结构特征、结合数学非线性时间序列预报方法应用于站点海面风和海面风场预报,总结相关方向关键技术的国内外研究进展,为下一步散射计海面风场资料在远洋航天气象保障中的深入应用及国内海洋二号卫星散射计资料的应用提供理论基础和方向支撑。     

用TOPEX/POSEIDON高度计数据分析热带大西洋海面高度距平的低频变化

利用1992年10月~2002年7月的TOPEX/POSEIDON(T/P)卫星高度计月平均格点数据分析了热带大西洋(15°S~25°N,5°~50°W)海面高度距平的低频变化。由热带大西洋大约10 a海面高度距平变化的标准差分析得到:在赤道附近海区(2°~5°N,25°~45°W)、非洲沿岸海区(11°~16°N,16°~18°W)海面高度波动剧烈。对海面高度距平进行经验正交函数(EOF)分析,得到EOF的3个模态分别占有方差比例为51.5%,13.2%和7.9%。第一模态揭示的是热带辐合带(ITCZ)的季节性迁移导致海面高度距平沿着ITCZ平均位置经向倾斜的1 a周期变化,第一模态还显示了太阳辐射的季节差异引起南北两个海盆海面高度的整体升降。第二模态描述了中心分别位于(3°N,40°W)和(7°N,45°W)附近两个涡漩的变化。第三模态表征的是几内亚海湾上升流和赤道北部下降流在6~7月强度达到最大。对EOF时间系数曲线的经验模态分解(EMD),结果表明热带大西洋低频变化包含的成分主要有:0.5,1,2,4和6 a。其中1 a周期是热带大西洋海面高度变化最主要的周期成分,0.5 a周期和2 a周期也是热带大西洋海面高度变化的重要形式;而4 a和6 a周期所占的比例较小。另外EMD方法还分解出1997~1998年太平洋El Nino事件对热带大西洋海面高度的影响。     

南海中北部热带气旋强度突变的天气气候特征分析

本文对1960-2002年在南海中北部活动的热带气旋进行分析统计,发现有如下气候特征：南海中北部平均每年有6.7个热带气旋,有4.9个热带气旋强度发生突变,其中有3%的热带气旋只发生突然增强,72%的热带气旋只发生突然减弱,25%的热带气旋既发生突然增强又发生突然减弱过程.强度突然减弱发生在4-12月,主要集中在登陆和登陆后的陆地区域,分布较广;强度突然增强发生在4-11月,主要出现在珠江口以西至海南岛东部海面、东沙群岛和西沙群岛海面.     

影响西太平洋台风形成的大尺度环流条件

根据全球热带气旋频率的统计^[1],这些频率有明显的年际变化。在过去二十年中全球热带气旋数年变化的百分率为其平均数的-13%-+23%,最多和最少年热带气旋数差达28个,相当于全球年平均热带气旋数(79)的35%。目前认为有三个原因可能影响热带气旋频率:大尺度环流,海面温度和地球以外的因子。     

西北太平洋热带气旋频数及生成位置的气候变化研究进展

自20世纪70年代末期以来,西北太平洋的热带气旋在全球变暖的背景下主要发生了两种宏观的气候变化：一个是热带气旋生成频数呈现年代际减少,尤其是在东南部海域;另一个则是其生成与活动位置等总体特征有向西北偏移的趋势。本文对这两个方面的研究进展进行了概述。近些年的研究表明,垂直风切变的增强可能是夏秋季热带气旋频数减少的最主要原因,这与太平洋-印度洋海面温度变化导致的大尺度环境变化有密切联系。同样有研究认为北大西洋海面温度的多年代际振荡对近期西北太平洋热带气旋生成频数的减少也非常重要。但西北太平洋西部强热带气旋的频数呈现出增加的趋势,这可能与东亚近海海面温度的显著升高有关,尽管这种变化是否可信仍有争议。近20年来,西北太平洋热带气旋活动普遍出现西北移倾向,包括生成位置和路径位置,这种变化可能受到了ENSO变异及20世纪90年代末期太平洋气候突变的调控。同时,热带环流的极向扩张又导致了热带气旋的有利环境向北扩张,因此西北太平洋热带气旋活动也出现极向迁移的趋势。     

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.     

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。     

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.     

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.     

Estimation of Sediment Properties during Benthic Impact Experiments

Sediment properties, such as water content and density, have been used to estimate the dry and wet weights, as well as the volume of sediment recovered and discharged, during benthic impact experiments conducted in the Pacific and Indian Oceans. The estimates show that the weights of dry (355-1332 t) and wet sediment (1651-4888 t) recovered during the experiments, are not only a function of the total duration and distance covered during the experiment, but also depend on water content and density of the sediment. Estimation of dry sediment and its volumetric ratio in the discharge, are key parameters for calculating the discharged volume. The estimated volume of wet sediment recovered (1427-4049 m 3 ) as well as discharged (2693-6951 m 3 ) during the experiments, provide important inputs to evaluate the sediment resettlement and migration. Using these estimates, the average depth of excavation on the seafloor, can also been calculated. However, the stages of sediment recovery and discharge are expressed differently in some of the experiments. In order to standardize these, different stages have been identified, and definitions of certain terms have been suggested, for use in the future. The methods of calculating different properties, as well as weight and volume of discharged sediment are described in the paper for use in other applications concerning deep-sea discharges.     

A Tidal Flow Model for the Gulf of Kachchh, India

A vertically integrated model has been used to study the tidal circulation and currents in the Gulf of Kachchh along the west coast of India. The model is fully nonlinear and uses a semiexplicit finite difference scheme to solve the basic hydrodynamic equations on a staggered grid. The model is forced by prescribing the tides along the open boundary of the model domain. The flow is simulated both with and without the presence of the proposed tidal barrage across the Hansthal Creek in the Gulf of Kachchh. The results show a considerable change in the behavior of the tidal flow in the presence of the barrage.