Momentum transport of wave zero during March: A possible predictor for the Indian summer monsoon

Analysis of monthly momentum transport of zonal waves at 850 hPa for the period 1979 to 1993, between ‡S and ‡N for January to April, using zonal (u) and meridional (v) components of wind taken from the ECMWF reanalysis field, shows a positive correlation (.1% level of significance) between the Indian summer monsoon rainfall (June through September) and the momentum transport of wave zero TM(0) over latitudinal belt between 25‡S and 5‡N (LB) during March. Northward (Southward) TM(0) observed in March over LB subsequently leads to a good (drought) monsoon season over India which is found to be true even when the year is marked with the El-Nino event. Similarly a strong westerly zone in the Indian Ocean during March, indicates a good monsoon season for the country, even if the year is marked with El-Nino. The study thus suggests two predictors, TM(0) over LB and the strength of westerly zone in the Indian Ocean during March.     

MODELING THE FATE AND TRANSPORT OF HYDROPHOBIC ORGANIC COMPOUNDS IN AN UNSTEADY RIVER-ESTUARINE SYSTEM

1 INTRODUCTION Extensive literature (Brown et al., 1985; Sawhney et al., 1981; Bierman and Swain, 1982; Connolly, 1980; Lopez-Avila and Hites, 1980; O扖onnor, 1988) described lots of sorbed pollutants or toxic substances in bed sediments of rivers, even after the effluent was halted for a long time. This is particularly true for hydrophobic organic compounds that can be sorbed on the particles and accumulated in the river bed sediments (Karickhoff et al., 1979). Pollution events of…     

The nature of calcareous deposits along pan margins in eastern central Namibia

In a region along the western margin of the Kalahari in eastern Namibia and western Botswana, many pan basins have mainly calcareous deposits along part of their margins. These are typically lined by low vertical scarps. In Namibia, these pans are mainly located in dry river beds. The petrographical study of these deposits demonstrates that they consist of lacustrine sediments that have to a varying extent been affected by early‐diagenetic processes and by the formation of late‐diagenetic features. The original composition of the deposits ranges from highly calcareous sediments, typically with ostracod, diatom and charophyte remains, to entirely non‐calcareous diatomites. The deposits generally show an upward increase in total carbonate content, which is mainly a synsedimentary feature. The early‐diagenetic processes that affected the deposits include the formation of orthic siliceous nodules. At a later stage, secondary calcite enrichment occurred, leaving only the silica‐impregnated sections unaffected. This enrichment partly accounts for the upward increase in total carbonate content in some profiles and often resulted in the development of a highly calcareous surface horizon. Sepiolite and amorphous silica that are part of the groundmass of the deposits may also partly have formed at this stage. Late‐diagenetic features include various forms of secondary calcite and silica. This study of pan basins in eastern central Namibia indicates that a lacustrine rather than purely pedogenic origin should also be considered for calcareous deposits that commonly occur along pan margins in other parts of southern Africa. Copyright © 2002 John Wiley & Sons, Ltd.     

Screening model for volatile pollutants in dual porosity soils

This paper develops mass fraction models for transport and fate of agricultural pollutants in structured two-region soils. Mass fraction index models, based on a semi-infinite domain solution, are derived that describe leaching at depth, vapor losses through soil surface, absorption, and degradation in the dynamic- and stagnant-water soil regions. The models predict that leaching is the result of the combined effect of the upward vapor-phase transport relative to downward advection, residence time relative to half-life, dispersion, and lateral diffusive mass transfer. Simulations show that leached fraction of volatile compounds does not always decrease monotonically with increased residence time relative to the pollutant half-life, as a result of complex interactions among the different physical and biochemical processes. The results show that leaching, volatilization, and degradation losses can be affected significantly by lateral diffusive mass transfer into immobile-water regions and advection relative to dispersion (i.e. Peclet number) in the mobile-water regions. It is shown that solute diffusion into the immobile phase and subsequent biochemical decay reduces leaching and vapor losses through soil surface. Potential use of the modified leaching index for the screening of selected pesticides is illustrated for different soil textures and infiltration rates. The analysis may be useful to the management of pesticides and the design of landfills.     

坝上高原安固里淖粒度年纹层与环境变化

在安固里淖湖心区获取一未扰动沉积物样柱，分析发现了由冬季风搬运物与湖心沉积共同形成的粒度年纹层，建立了纹层年表，恢复了安固里淖湖区8507aB.P，以来的环境变化过程。8507-5429aB.P。冬季风活动较弱，后期的所波动；5429-3244aB.P.冬季风活动较强，3244-2494aB.P。冬季风活动减弱；2494-1165aB.P。冬季风活动略有增强；1165aB.P以来，冬季风活动减弱。安固里小淖粒度年纹层反映的冬季风变化情况与我国北方地区同期的环境变化和海平面变化有很好的对应关系。     

应用遥感技术分析廉州湾悬沙的动态特征

该文依据美国陆地卫星 (Landsat)接收的MSS、TM资料 ,得到廉州湾海区表层悬沙分布的解译图 ,分析廉州湾及湾外海区水流流场特征、悬沙的分布及输移扩散特征 ,并就潮流、径流等水动力对湾内悬沙运动、滩槽冲淤的作用和影响进行了讨论     

山东月湖的沉积物分布特征及搬运趋势

1998年 11～ 12月和 1999年 8～ 9月各一个月对月湖进行的野外工作 ,共取得表层沉积物样品 131个 ,应用激光粒度仪并结合传统的筛分法对这些样品进行粒度分析 ,进行矩法计算获得粒度参数。采用Gao命名方法 ,将沉积物划分出 5种主要类型。利用Gao -Collins粒径趋势分析模型 ,计算该区沉积物粒径趋势所显示的沉积物净搬运方向 ,结果表明 ,沉积物从四周向湖中心搬运 ,同时显示湾顶的西部和北部、涨潮三角洲以及湖心等地貌单元是沉积的优势区域。     

GIS与土壤溶质运移模型结合研究进展

地理信息系统对土壤溶质模型研究而言，使用者的要求与GIS所能提供的功能之间，还存在巨大的差距。出于对环境问题的关注，土壤中水分及溶质运移的规律及其对环境的影响，成为当前研究的热点。随着对土壤溶质运移模型研究的深入，一方面由于田间土壤特性具有很大的空间变异；另一方面，在实际应用中，往往溶质运移的宏观特征而非微观特征，具有更重要的意义。将溶质运移模型与GIS技术结合，定量研究空间尺度的溶质运移，成为溶质运移研究的必然发展趋势。由于计算机软硬件技术的发展，GIS正处于一个高速发展的时期。将GIS与溶质运移模型相结合，或者进一步，以GIS理论和技术为基础，建立基于GIS的溶质运移模型，将对溶质运移的规律及其对环境的影响，做出更深入和准确的描述。     

三种被动式积沙仪积沙效率的野外实验研究

积沙仪积沙效率的高低直接影响近地表输沙率的测定，从而影响着风沙地貌的研究和风沙工程设计，对目前三种常用积沙仪在相同条件下（同一下垫面、相同风速）的积沙进行了野外观测。结果表明：（1）相同条件下，楔形积沙仪积沙量远远大于其它两种；（2）近地面积沙量随高度分布上，楔形积沙仪能更好地反映风沙流结构；（3）与其它两种积沙仪相比，楔形积沙仪所采集沙子中的小粒径颗粒含量明显多于其它两种积沙仪结果，而较大粒径颗粒的含量呈相反趋势，造成这些差异的原因在于楔形积沙仪采用的流线型构造和网状结构，从而对风沙流的阻挡程度较小，今后应推广楔形积沙仪的使用。