Correspondence Between Astronomical Periods and Sedimentary Cycles

The term of geological cycle was used firstly inHutton's" The Earth Theory" in 1788 (Williams,1980). The geological cycles including tectonic cycles and sedimentary cycles have been describedwidely since than. Some researchers have perceivedthat the geolo…     

有机碳同位素示踪古环境变化研究

对有机碳同位素示踪环境变化的原理、研究对象、取得的进展和存在的问题等进行了详细研究，认识到C～H键比C-O键有利于富集^12C，从而导致生物或有机碳δ^13C为极低的负值，使有机碳与无机碳之间存在显著的碳同位素差异。光合作用类型的不同使植物分为C3，C4和CAM3种类群，并导致不同类群的植物具有不同的碳同位素组成，C3植物δ^13C=-20‰～-32‰，平均-28‰，而C4植物δ^13C=-9‰～-17‰，平均-14‰。气候环境的差异影响了光合作用的类型和强度，使不同环境的植物类群特征不同，不仅造成植物组合的碳同位素组成不同，而且导致不同食性的动物牙齿等化石的碳同位素组成的差异，甚至相应的无机碳同位素的变化，因此生物链及其衍生物的碳同位素研究也就成为反演某一地区或某一时期气候环境的有效手段。被作为研究对象的地质记录可分为有机和无机两类，有机类主要包括树轮等植物化石、牙齿等动物化石、煤等陆相沉积有机质、海相沉积有机质、土壤(前者的衍生物)，这些研究对象分别适合于目的不同的环境研究，并获得了较好的效果。进而发现有机碳同位素在研究重大生物灭绝事件、C4植物起源、地球早期生命起源、地外生命存在与否、矿产资源形成时的有机质作用等问题上将有重要作为。     

热带西太平洋热状况年代际和年际变化特征分析

采用谐波分析和EOF分析方法,对比研究了暖池区域表层热状况(海表温度距平SST'表征)和浅层热状况(热含量距平HS'和次表层海温距平ST'表征)在1月和7月的年代际、年际尺度时空特征.分析结果表明:⑴不同季节的年代际、年际尺度SST'和HS'都存在两个显著模态,HS'1月的年代际、年际尺度结构最简单,而SST'7月的年代际和1月年际结构最复杂;⑵ 1970年代末和1980年代初发生的年代际跃变HS'晚于SST', 且SST'(HS')呈增温(减少)趋势;⑶ HS'的年际异常与ENSO关系密切,而SST'与ENSO关系不显著.     

近30年夏季亚欧大陆中高纬度阻塞高压的统计特征

文中利用1970～2001年NCEP再分析500 hPa逐日高度场资料,根据阻塞高压的天气学定义,采用客观统计方法检索出近32 a亚欧中高纬度392个阻塞高压个例,对其进行了气候学分析.结果表明,亚欧中高纬地区夏季阻塞高压活动频繁,10 d以下的过程占绝对多数,地理分布主要集中在45～70°N之间,纬向上可划分5个高发区,其中乌拉尔山和贝加尔湖东部阻高活动频次最高,同时,每个区域中又存在着相应的阻高活跃区.亚欧中高纬地区夏季阻高活动具有明显的季节内变化特征.6月份,阻塞活动多发生在乌拉尔山地区和鄂霍次克海地区,以双阻为主要形势;7月份,欧洲区和贝加尔湖地区的阻塞活动有所增多,尤其贝加尔湖东部地区增多明显,而乌拉尔山地区的阻塞形势明显减少,鄂霍次克海地区的阻塞活动位置向北移动,多发生在60°N以北,双阻形势逐渐减弱,贝加尔湖地区的中阻形势有所增强.8月份,阻塞形势主要存在于贝加尔湖东西两区,中阻形势占据主导地位.亚欧中高纬地区夏季阻塞高压活动年际变化特征也很突出,且这种年际振荡有明显的地理差异.另外,研究表明亚洲北部的阻高活动多以稳定型为主,移动型阻高个例仅占6.6%.移动型阻高以起源于乌拉尔山地区最多,移距最长,生命期最长.偶极子类阻高多集中在贝加尔湖东部与乌拉尔山地区,约占该地区总阻高频次的62.0%和49.7%,平均生命期分别达到7 d/次和9 d/次以上.     

一种台风海面非对称风场的构造方法

针对台风数值预报中由于采用对称模型而导致预报误差的现实，通过引入非对称分布的台风最大风速、最大风速半径等因子，在得到台风报告中7级风和10级风的半径的基础上，利用最佳权系数方案来得到非对称的台风外围风速分布因子，从而对Chan and Williams 1987年提出的切向风廓线方案进行改造，进而得到了台风海面非对称风场的计算式。检验表明，该方法能够描述台风海面风场的非对称分布，具有较好的应用前景。     

冬春季切变类冰雹发生条件的对比分析

本文以 1996年 12月 31日和 1981年 5月 1日为例 ,对冬、春季节发生在江苏的较大范围的切变类冰雹天气过程作了对比分析。结果指出 ,无论冬季或春季当高原东部有深槽东移 ,冷暖空气在江淮地区交汇 ,地面抬升系统为暖切 ,并有大气层结不稳定 (Δθse( 50 0 - 850 ) <0℃ =中心和较强的风向和风速垂直切变、85 0hPa西南急流轴、85 0hPa最大水汽通量轴线、5 0 0和 85 0hPa正涡度中心等相配置时 ,就可能导致江苏地区较大范围强对流天气的发生。     

Enhancement of the method of summer precipitation forecasting

The physical-synoptic principles of the automated method of summer precipitation forecasting introduced into operational prognostic practice in 2006 by the decree of the Central Methodical Commission of the Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) are presented. Beside that, improved modifications of this method, which are automatically updated, are shown. Validation of those updates based on observational data collected in 2004 has shown improvement of all major criteria of forecasts efficiency. The performed improvement is based on the more detailed quantitative realization of mechanism of various showers formation (including heavy rainfalls).     

Authigenic iron and titanium oxides in triassic red beds: (St. Bees Sandstone), Cumbria,Northern England

Authigenic iron and titanium oxides occur in three main textural varieties in the St. Bees Sandstone, a Triassic red bed succession in Cumbria. These are: (a) overgrowths of haematite, titaniferous haematite, anatase, and rutile which generally occur on detrital host grains of similar compositions. The overgrowths may occur as syntaxial rim cements or rhombohedral and prismatic projections and are always in optical continuity, (b) discrete crystals of anatase (including octahedrite) and haematite 10-40 μm in size occur in pore spaces, and (c) fine grained ( < 1 μm) pigmentary haematite occurs as grain coatings around detrital grains and in the interstitial matrix. The euhedral nature and pore-filling habit clearly indicate the authigenic origin of these iron- and titanium oxides. All three textural varieties are believed to have been precipitated from ground waters containing dissolved ferrous and titanium ions. These ions were derived from the intrastratal solution of detrital iron and titanium bearing grains including ferromagnesian silicates and iron-titanium oxides. The precipitation of iron oxides from migrating ground waters in the manner described here goes some way to explaining how thick, uniformly red successions can be formed.     

Formation Mechanism of Mud Bank Along the Southwest Coast of India

Mud bank formation during the southwest monsoon along the southwest coast of India remains an enigma to the researchers and coastal community in spite of several earlier studies. The present study attempts to unravel the mystery through a high-frequency, season-long time-series observation at Alappuzha, located at the southern part of the west coast of India, a region of frequent occurrence of mud bank. Using 7-month-long weekly time-series observation, we identified strong winds and high waves associated with onset of the southwest monsoon and subsequent three episodic atmospheric low-pressure events (LPEs).With the help of in situ time-series data, we show that the strong winds and high waves associated with southwest monsoon pre-conditions the near shore bottom sediment to bring it into suspension. The high amplitude waves associated with the southwest monsoon, while propagating from the deep water to shallow water region, interact with the bottom initiating bottom-sediment movement and its suspension due to wave refraction and shoaling. The sporadic occurrence of the atmospheric LPEs enhances the process of suspension of bottom sediment in the near shore region leading to the formation of fluid mud. Simulations with a cohesive sediment transport model yielded realistic estimates of sediment transport, in the presence of an onshore current, a pre-requisite for transporting the fluid mud toward the coast. The prevailing onshore upwelling current during the southwest monsoon provides the favorable pre-requisite conditions for transporting the fluid mud through depression channel network towards the coast. Once sufficient quantity and thickness of fluid mud is accumulated in the near shore region, it acts as a wave damper for subsequent high monsoon waves, as indicated by the time-series wave data, leading to the formation of tranquil mud bank region. Depression channel networks extending from the shelf to the coast off Alappuzha, Kochi, Ponnani, Beypore, and Ullal were found in the bathymetric charts, thus explaining why mud banks occur only at few locations in spite of the prevalence of similar monsoon conditions.