多普勒声雷达测风与直接测量仪器的观测比较

文中对多普勒声雷达测风和325 m铁塔上风速、风向仪及超声风速仪的测量值进行了观测比较。结果表明,当信噪比大于1时,两种方法测量的平均风速、风向的相关较好,风速、风向廓线较为接近;声雷达测量的垂直风速平均值和均方根差比超声风速仪的测量值略偏大。这与国外进行的观测比较结果一致。 需要指出,声雷达和直接测量仪器的观测比较中存在一定差异,特别是对比每一次的观测值就可以看出,在某些情况下还存在明显差异。进一步分析声雷达测风产生偏差的原因,对误差做出合理的订正是十分必要的。     

Oxygen budget of a perennially ice-covered Antarctic lake

A bulk O2 budget for Lake Hoare, Antarctica, is presented. Five years of seasonal data show the lake to be persistently supersaturated with O2. Oxygen is carried into the lake in glacial meltstreams and is left behind when this water is removed as ice by ablation and sublimation. A diffusive loss of O2 from the lake through the summer moat is suggested. Measured values of the total O2 in the water column indicate that the time scale of O2 turnover is much longer than a year. Based on these results we suggest that the amount of O2 in the water does not change significantly throughout the year and that the lake is also supersaturated with N2.     

中尺度对流系统产生强降水的临近预报方案

一、前言国家环境卫星、数据和情报服务处(NESDIS)在业务上应用卫星资料估算降水量的工作已有十多年了.在此工作的基础上,NESDIS现正在开发一个暴洪估算模型和临近预报方案(PROFFENS).临近预报方案包括现在天气的详细描述以及未来0-12小时的短期预报两部分(Scofield和Weiss,1977).PROFFENS的研制包括分析降了多少雨以及预报未来0-12小时内将出现多少     

输入海洋的大气化学物质

引言 数十年来,海洋科学界一直关注着对进入海洋的源于大自然及人类的物质的估算和过程的了解.在这一领域早期的工作集中于由河流和江川带入海洋的明显的物质输入,随后的研究考查了下水道排放、倾倒等直接输入途径.然而近十至二十年来,已经搞清楚大气层不仅是将自然物质和污染物质从陆地输往海岸和海洋的一个重要途径,在有些情况下甚至是主要途径.这些物质包括矿物粉尘、厂矿残渣;燃烧过程释放的含氮物质、化肥;杀虫剂及来源于各种工业及民用生产过程的其它有机化合物.     

Radar determination of the spatial structure of hydraulic conductivity

Spatial variability of hydraulic conductivity exerts a predominant control on the flow of fluid through porous media. Heterogeneities influence advective pathways, hydrodynamic dispersion, and density-dependent dispersion; they are, therefore, a key concern for studies of ground water resource development, contaminant transport, and reservoir engineering. Ground-penetrating radar contributes to the remote, geophysical characterization of the macroscale variability of natural porous media. On a controlled excavation of a glacial-fluvial sand and gravel deposit in the Fanshawe Delta area (Ontario, Canada), the hydraulic conductivity field of a 45 x 3 m vertical exposure was characterized using constant-head permeameter measurements performed on undisturbed horizontal sediment cores. Ground-penetrating radar data were collected along the excavation face in the form of both reflection and common midpoint surveys. Comparison of geostatistical analyses of the permeameter measurements and the radar data suggests thatthe horizontal correlation structure of radar stack velocity can be used to directly infer the horizontal correlation structure of hydraulic conductivity. The averaging nature of the common midpoint survey is manifest in the vertical correlation structure of stack velocity, making it less useful. Radar reflection data do not exhibit a spatial structure similar to that of hydraulic conductivity possibly because reflections are a result of material property contrasts rather than the material properties themselves.     

Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution

Planetary nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations from our LMC PN morphological survey, and including images available in the Hubble Space Telescope Data Archive and published chemical abundances, we find that asymmetry in PNe is strongly correlated with a younger stellar population, as indicated by the abundance of elements that are unaltered by stellar evolution (Ne, Ar, and S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extragalactic PNe. We also examine the relation between morphology and abundance of the products of stellar evolution. We found that asymmetric PNe have higher nitrogen and lower carbon abundances than symmetric PNe. Our two main results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNe have on average larger masses than the progenitors of symmetric PNe. The results bear on the question of formation mechanisms for asymmetric PNe-specifically, that the genesis of PNe structure should relate strongly to the population type, and by inference the mass, of the progenitor star and less strongly on whether the central star is a member of a close binary system.