乌兰布和沙漠降水入渗补给对气候变化的响应

为探究地下水补给对气候变化的响应,以乌兰布和沙漠为例,基于氯质量平衡法,通过野外打钻和室内离子分析,重建区域地下水补给历史和短时间尺度的气候变化过程。结果表明：降水对沙漠地区的地下水补给非常小,对比周边地区记录发现,地下水补给呈现出由西向东逐渐增大的趋势,且一定程度上反映出贺兰山对季风气流的阻挡作用,在相关季风较弱年份,贺兰山西侧降水补给弱于东侧。过去600年来本地区的气候波动大,1455-1500 AD、1600-1650 AD是气候较为干旱的时期,18世纪末至19世纪初是环境演化一个重要的时间界限,自此以后的漫长时间,干旱化进程进一步加剧,尤其是1920-1930 AD,区域极端干旱。本研究也验证了处于季风边缘沙漠地区降水入渗补给对气候变化所呈现出的响应差异。     

湖南资水流域切变线天气形势下中β尺度对流系统的数值模拟研究

本文对湖南资水流域700hPa层呈现相似切变线天气形势的两次天气过程进行了研究,其中一次是2001年6月19日08BST出现大暴雨,另一次是2001年8月13日08 BST至14日08 BST仅出现小雨,文中对这两个个例进行中尺度数值模拟,对比分析了这两个个例演变过程的差异,并对6月19日中β尺度对流系统在暴雨强盛期的动力结构特征和热力结构特征作了详细分析。研究结果表明6月19日在演变过程中生产的中β尺度对流系统引发了这次暴雨,而8月13日虽然有类似于6月19日的切变线,但是没有形成中β尺度对流系统,也就没有引发暴雨。由此表明,相似的700hPa形势可以有根本不一样的演变,而暴雨的发生与中β尺度对流系统的生产和发展有十分密切的关系。     

飞机人工增雨空地传输网络系统

利用陕西省人工影响天气中心和西安精博科技有限公司共同研制的飞机增雨空地传输系统,于2002～2003年在增雨飞机上进行了25架次的试验。该系统的结构特点是：采用无线和有线相结合的传输模式,克服了短波通信中信号不稳定的现象,达到了语音和数据传输基本正常。经对2003年9月19日增雨飞机上接收的温度、湿度、飞行高度、飞机轨迹图与地面实时接收的上述数据对比分析,发现在同一时间所传输的数据与飞机上的数据基本吻合,地面指挥人员能及时了解到增雨飞机的各种情况。该飞机增雨空地传输系统能实现地面指挥人员与空中作业人员的实时通话和数据传输,实际运行情况良好。     

基于VGOS单基线的UT1测定能力评估

对2021年VLBI (Very Long Baseline Interferometry)全球观测系统(VLBI Global Observing System,VGOS)单基线开展的1 h世界时(Universal Time, UT1)加强观测数据进行分析,结果表明, VGOS单基线测得的UT1与IERS (International Earth Rotation Service) C04序列提供的UT1之差的RMS (Root Mean Square)为25.3μs,优于传统S/X双频段UT1加强观测(Intensive observation, INT1)试验的28.2μs,且UT1的平均形式精度提高1倍.因VGOS单基线1 h观测数目比INT1多1倍,其测得的UT1受极移误差的影响更加稳定,每100μas的极移误差将对UT1引入2.8μs的偏移.此外分析了VGOS 30 min观测数据,除平均形式精度变差外, UT1测量结果与1 h结果相当,表明VGOS单基线30 min观测可用于UT1的超快速服务.同时分析和评估了2021年国内佘山与南山13 m VGOS基线的UT1加强观...     

秦巴山地盛夏连阴雨中的局地强降水数值模拟及诊断分析

秦巴山地局地强降水是青藏高原东部典型的气象灾害之一,对当地工农业生产影响极大.采用常规气象观测资料分析了秦巴山地2005年7月1～10日连续10天降水过程,侧重分析了7月8日夜间的一次局地强降水,并利用wRF-V2.1中尺度非静力模式对7月8日的局地强降水过程进行了数值模拟和诊断分析.结果表明:此次连阴雨天气是在西太平洋副热带高压稳定少动的大尺度环流背景下产生的,中尺度低空急流对中尺度低涡系统的发生发展有加强和促进作用,低层辐合和高层辐散是降水系统发展的动力条件.     

Agrochemical and polychlorobyphenyl (PCB) residues in the Mekong River delta, Vietnam

An environmental survey on pesticide residues and polychlorobyphenyl compounds (PCBs), encompassing more than 70 polar and non-polar compounds quantifiable by the techniques used, was performed in the Mekong River delta based on analyses of water, sediment and bivalve mollusc samples. Few polar compounds, such as diazinon and fenotrothion, were detected in water but a high number of non-polar chlorinated compounds, such as DDT, HCH, endosulfan and PCBs, were detected in sediments and biota. The highest concentrations measured were of DDT with an average 6.3 ng g(-1) dry weight (range 0.32-67 ng g(-1)) in sediments and 38.6 ng g(-1) (range 5.5-123 ng g(-1)) in molluscs' soft tissues. Amongst chlorinated compounds, DDT concentrations were followed in decreasing order by those of PCB, endosulfan, hexachlorocyclohexane and chlordane. Residues of organochlorine compounds originate from local usage of agrochemicals although with a likely contribution also of atmospheric deposition of residues (not measured) originated elsewhere. Concentrations of PCB and pesticide residues in the aquatic environment of the Mekong River delta are lower than values reported for other regions of Vietnam and Asia. Nevertheless, current concerns about the effects of chlorinated compounds on public health advise improved control of chemical residue discharges in order to abate environmental contamination.     

景观生态系统的空间结构：概念、指标与案例

空间结构分析是景观生态学研究的重要内容和基本特色之一。讨论了景观生态系统的空间结构概念,提出斑,廓,基,缘是空间结构的四个主要元素。认为对景观生态系统空间结构的分析,可以分三个不同的等级层次进行,一是宏观尺度的整体空间构架,二是中观尺度几种典型的空间组合型;三是空间元素的基本形态特征。     

The Stability and Existence Condition of Nonlinear Travelling Wave Solution in Basic Uniform Flow

Summary  Nonlinear waves in a stratified atmosphere with basic uniform flow are studied by adopting geostrophic momentum approximation (cf. Hoskins, 1975) and the method of travelling wave solution. A nonlinear equation containing a unique variable of vertical p velocity is derived from a complete system of equations considering frictionless and adiabatic fluid. The stability of the solution for the nonlinear equation is discussed then. Furthermore, the approximate cnoidal wave solution, solitary wave solution and their existence condition are obtained. Received July 8, 1998 Revised December 1, 1998     

Modelling bivariate extreme precipitation distribution for data‐scarce regions using Gumbel–Hougaard copula with maximum entropy estimation

A new method of parameter estimation in data scarce regions is valuable for bivariate hydrological extreme frequency analysis. This paper proposes a new method of parameter estimation (maximum entropy estimation, MEE) for both Gumbel and Gumbel–Hougaard copula in situations when insufficient data are available. MEE requires only the lower and upper bounds of two hydrological variables. To test our new method, two experiments to model the joint distribution of the maximum daily precipitation at two pairs of stations on the tributaries of Heihe and Jinghe River, respectively, were performed and compared with the method of moments, correlation index estimation, and maximum likelihood estimation, which require a large amount of data. Both experiments show that for the Ye Niugou and Qilian stations, the performance of MEE is nearly identical to those of the conventional methods. For the Xifeng and Huanxian stations, MEE can capture information indicating that the maximum daily precipitation at the Xifeng and Huanxian stations has an upper tail dependence, whereas the results generated by correlation index estimation and maximum likelihood estimation are unreasonable. Moreover, MEE is proved to be generally reliable and robust by many simulations under three different situations. The Gumbel–Hougaard copula with MEE can also be applied to the bivariate frequency analysis of other extreme events in data‐scarce regions.     

Climate tipping-point potential and paradoxical production of methane in a changing ocean

The global warming potential of methane (CH₄) is about 30 times stronger than that of carbon dioxide (CO₂) over a century timescale. Methane emission is hypothesized to have contributed to global climate change events and mass extinctions during Earth’s history. Therefore, the study of CH₄ production processes is critically important to the understanding of global climate change. It has been a dogma that biogenic CH₄ detectable in the oceans originates exclusively from the anaerobic metabolic activity of methanogenic archaea in hypoxic and anoxic environments, despite reports that many oxic surface and near-surface waters of the world’s oceans are CH₄-supersaturated, thereby rendering net sea-to-air emissions of CH₄. The phenomenon of CH₄ production in oxic marine waters is referred to as the “ocean methane paradox”. Although still not totally resolved, recent studies have generated several hypotheses regarding the sources of CH₄ production in oxic seawater. This review will summarize our current understanding of the importance of CH₄ in the global climate and analyze the biological processes and their underpinning mechanisms that lead to the production of CH₄ in oxic seawater environments. We will also tentatively explore the relationships of these microbial metabolic processes with global changes in climate and environment.