ENSO对华东地区春季降水影响的不对称性

利用1958—2019年的观测和再分析数据集,对冷、暖两类厄尔尼诺-南方涛动（El Niño-Southern Oscillation,ENSO）事件与后期华东地区春季降水之间的关系进行了分析。结果表明：（1）在暖ENSO事件中,华东春季降水量与前冬季ENSO海面温度异常存在较强的正相关关系。在冷ENSO事件中,这种强正相关向内陆地区西移,主要集中在江西和湖南。（2）暖ENSO事件通常会导致浙江、江苏和福建等沿海省份春季降水量过剩,而冷ENSO事件往往导致江西和湖南降水偏少。这归因于ENSO对大气环流的非线性影响。（3）与暖ENSO事件相比,冷ENSO事件引起的海面温度异常中心明显西移,造成异常低层大气环流的西移,最终导致华东降水的西移效应。（4）通过分析和发现,强调了华东春季降水对ENSO的非线性响应,这对华东地区的季节性气候预测具有重要意义。     

春季青藏高原感热通量对不同海区海温强迫的响应及其对我国东部降水的影响

本文利用在青藏高原适用性较好的ERA-interim地表感热通量资料,研究了1981-2010年青藏高原春季地表感热通量的年际变率与前期不同海区海温强迫的联系,以及这种联系对我国东部降水可能造成的影响。结果表明,春季青藏高原地表感热通量的年际变化有两个主要的模态,分别与前期太平洋以及印度洋海温有密切联系。与冬季ENSO事件相应的赤道中东太平洋海温强迫可以激发一个向极向西的波列,通过改变青藏高原南侧的环流和降水异常,形成一个纬向偶极型分布的高原感热第一模态,其对应的时间序列主要表现为准5 a的振荡,与ENSO事件的周期较为吻合;而春季印度洋的三极型海温分布可以强迫出一个跨越南北半球的波列,使青藏高原主体表现为东风异常,减弱背景西风,从而形成一个青藏高原主体与周围反相关的回字形感热第二模态,其主要呈现5~7 a的振荡周期。ENSO事件以及印度洋海温分布分别与青藏高原春季感热两个主模态相联系,并且冬春季海温与高原春季感热主模态对我国东部春季降水有协同影响,对于我国北方降水异常而言,高原的贡献相对海洋更重要。     

北半球冬季南太平洋海表温度异常的主要模态及其与ENSO的关系

利用新版本的NOAA扩展重构的海温资料,研究了1950/1951年-2008/2009年北半球冬季(12月-翌年2月平均)南太平洋海温异常的主要模态,并探讨了海温主要模态在年际和年代际时间尺度上与ENSO的关系。研究结果表明:北半球冬季南太平洋海温变化主要存在两个模态,第1模态基本反映了南太平洋海温异常南－北的反相变化特征,第2模态基本反映了南太平洋海温异常东－西的反相变化特征。两个模态的年代际周期均比其年际周期显著,其中第1模态的主要年代际周期为11~16 a,第2模态的主要年代际周期为18~24 a。主要模态与ENSO关系的分析表明,第1模态与同期ENSO事件的关系最显著,主要显示其对ENSO的响应,而第2模态对滞后其1 a的ENSO事件存在一定的影响。为进一步研究它们的年际和年代际关系特征,分别对它们进行滤波后的分析表明,在年际时间尺度上,南太平洋海温两个主模态同ENSO事件的关系与滤波前的基本一致;在年代际时间尺度上,第1模态的年代际变化可能对ENSO的年代际变化存在一定的响应,而第2模态可能不仅对前期的ENSO事件存在一定的响应,还可能对后期的ENSO事件存在一定程度的影响作用。     

一次“双谷”型ENSO冷事件的成功预测

2011年春季利用基于Morlet小波分析的余弦函数叠加法对中东太平洋的ENSO冷事件(La Nina)未来发展进行预测,结果成功地预测出了一次呈现"双谷"型的ENSO冷事件发展过程。此方法拟合的1980年1月—2011年2月的Nino3.4指数序列与原序列的相关系数为0.68;对2000—2011年间7次ENSO事件预测结果检验,发现提前3、6、9和12个月时Nino3.4指数的平均预报相关系数(R)分别为0.79,0.81,0.83和0.64,平均预报技巧得分(SS)分别为0.87,0.80,0.80和0.27。此方法具有计算简便,易于运行,预报时效稳定的特点,特别在提前6—9个月时对ENSO的预测仍有较好效果。     

台湾西南部海域风应力旋度偶极子的季节和年际变化分析

利用1995~2013年间NCEP风场资料,分析研究了台湾西南部海域风应力旋度偶极子的季节和年际变化特征,及其受ENSO事件的影响,结果表明:台湾西南部海域风应力旋度偶极子的分布存在明显季节变化,其分布期主要集中于每年10月至次年4月,夏季台湾海峡不存在风应力旋度偶极子的分布;风应力旋度偶极子的强度异常要滞后ENSO 1个月,当厄尔尼诺事件发生时,风应力旋度偶极子的分布强度较正常年份要弱,而当拉尼娜事件发生时,风应力旋度偶极子的分布强度较正常年份要强;风应力旋度偶极子的分布还存在准16.0个月和准45.3个月的显著年际变化周期,其变化同ENSO循环密切相关.     

中国东南春季降水异常特征及其与ENSO关系的年代际变化

利用中国160站观测降水资料和美国NOAA ERSST海温资料以及NCEP/NCAR再分析资料,研究了中国东南地区春季降水异常特征及其与ENSO关系的年代际变化。结果表明:东南春季降水异常具有全区一致性,在1950年代末之前有不显著的上升趋势,之后一直呈现下降趋势,其中在1960年代初至1970年代初下降趋势显著,1980、1990年代趋势较为平稳,1999年之后下降趋势增加。在过去64年中,中国东南春季降水与ENSO有显著的相关关系,即在El Ni珘no事件发生的次年春季,东南地区一般降水偏多,其主要机制为ENSO通过影响西北太平洋异常反气旋进而影响中国东南地区春季降水,并且利用前冬季Ni珘no3区海温指数可提前4个月较好地预测东南地区春季降水。进一步分析表明,东南春季降水与ENSO的相关关系具有年代际差异:在1969—1990年间两者相关性较好;而在1951—1968年和1991—2014年间,两者相关性较弱。在不同时间段内,与东南春季降水相应的春季环流系统有较大差异,ENSO作为影响因子的重要性也发生变化。在1951—1968年,影响降水的环流系统主要位于中高纬度,而西北太平洋反气旋位置较为偏东,难以影响到中国东部地区;在1969—1990年,副高和西北太平洋异常反气旋是影响东南春季降水的主要环流系统,反气旋西侧气流是提供水汽的主要来源;在1991—2014年,东南春季降水受到高低纬环流系统共同影响,来自印度洋西风气流和西北太平洋反气旋西侧气流共同为降水提供水汽,ENSO的作用减弱。因此,在中国东南春季降水预测中必须根据不同年代际背景考虑ENSO作为预报因子的可靠性。     

淮河流域5～6月降水的年际及年代际变化

对淮河流域降水异常进行分析对于预测黄海绿潮具有重要意义。选取淮河流域10个站,长江流域15个站,通过对国家气象信息中心1951~2011年的逐月降水数据进行分析,研究淮河流域和长江流域5~6月平均降水异常。2000~2010年,淮河流域5~6月降水呈现增加趋势,与长江流域降水呈反位相变化。分别对淮河流域5~6月平均降水异常与印度洋偶极子指数(Dipole Mode Index,DMI),以及太平洋年代际振荡(the Pacific Decadal Oscillation,PDO)指数做相关性分析,结果表明:淮河流域5~6月平均降水异常与6个月前的DMI指数达到最大正相关,与20个月前的北太平洋(20°N以北)SST呈现明显的负相关,与PDO指数达到最大负相关。这表明,PDO、DMI指数对淮河流域5~6月降水异常的年代际、年际变化具有明显的指示作用。     

ENSO事件中热带太平洋上层海洋热含量变化分析

利用1955-2001年海洋上400m层的热含量资料，分析了20世纪60年代以来全部El Nino／La Nina事件期间上层海洋热含量异常的空间分布规律和传播特性，发现如下3个重要观测事实：(1)在ENSO循环期间存在着关于赤道对称的南北2个热含量异常信号的闭合传播路径；(2)北半球的信号闭合回路非常清晰，而南半球回路较为混乱；(3)这种闭合回路在El Nino／La Nina年份表现得非常明显，但在其它年份可能由于海洋或大气的条件不匹配而中途夭折。上述观测事实对于ENSO研究具有重要价值，其物理机制值得进一步探讨。     

太平洋年代际涛动对ENSO与华南冬季降水关系的可能影响

基于中国160站冬季降水资料、NCEP/NCAR再分析资料以及NOAA SST资料,本文分析了太平洋年代际涛动(PDO)不同位相时期ENSO事件对华南冬季降水影响的差异。结果表明:在PDO正位相时期,El Nio年华南冬季降水显著增加,而La Nia年华南冬季降水没有明显变化;在PDO负位相时期,El Nio年华南冬季降水增加虽然显著,但仅是PDO正位相时期的一半,而La Nia年华南冬季降水显著减少,这说明PDO对ENSO事件影响华南冬季降水具有调制作用,且El Nio(La Nia)事件对华南冬季降水的影响在PDO不同位相时期具有不对称性。前人研究指出,El Nio(La Nia)事件主要通过西北太平洋异常反气旋(气旋)影响华南冬季降水。本文分析发现,在PDO正位相时期,El Nio年西北太平洋异常反气旋北侧西南气流影响华南,造成降水增加,而La Nia年西北太平洋异常气旋位置向南推,对华南地区影响很小;在PDO负位相时期,El Nio年西北太平洋异常反气旋位置东移,对华南影响不大,而La Nia年华南地区基本为西北太平洋异常气旋北侧东北风异常所控制,从而使降水减少。由此可见,PDO不同位相时期El Nio(La Nia)事件影响华南冬季降水异常差异的主要原因是西北太平洋异常反气旋(气旋)的差异造成的。此外,源自孟加拉湾低槽南侧的西风水汽输送异常在PDO不同位相时期El Nio(La Nia)年份也存在非对称性的差异。     

热带太平洋次表层三维海温距平场的EOF分析

应用太平洋次表层海温距平资料构造了一个立体的西低东高的四级阶梯模型,使用EOF方法对此模型进行时空分解,重点讨论了分解结果与ENSO循环的关系,并对Nino 3距平指数进行试预报,结果表明,用 EOF分解的第一主分量代表暖池-厄尔尼诺(拉尼娜)模态,第二主分量代表次表层温度距平的东西运移模态,厄尔尼诺事件正是东西运移模态突变的结果.时滞相关分析估算,一次ENSO循环的平均周期约为41个月,厄尔尼诺、拉尼娜模态与温度距平的东西运移模态的位相差平均约为9.7个月.应用逐步回归方法得到超前Nino 3距平指数3、6和12个月的3个预报方程.预报结果表明,第一、第二时间系数对Nino 3距平指数均具有一定的预报价值,预报时效可达1 a左右.     

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.     

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。     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone.     

Flow Cytometric Analysis of Coastal Lagoon Bacterioplankton and Picophytoplankton: Fixation and Storage Effects

The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics.     

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.     

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,