达尔文气压变化与蒙古东北部降水的关系研究   总被引：2，自引：1，他引：2  

王会军 《大气科学》2006,30(5):753-758

达尔文港是气象工作者非常熟悉的地名,因为南方涛动就是由达尔文和塔希提岛两个站的气压之差来定义的,达尔文港的气压(DP)可以代表澳大利亚北部海洋性大陆地区的气压.因此,作者的研究目的就是揭示该区域气压系统的变化与蒙古东北部降水的关系.结果表明,DP的正位相和区域低层大气辐散、高层大气辐合环流相关连,在亚洲对流层上层是异常西南风,对流层下层是异常偏北风,东亚季风减弱,在蒙古东北部地区的异常风为西北向,即,由内陆地区吹向西北太平洋地区,这意味着水汽由海洋向蒙古地区的输送减弱了,从而造成了降水的减少.反之亦然.  相似文献   

梅雨期中国东部降水的时空变化及其与大气环流、海温的关系   总被引：17，自引：7，他引：17  

宗海锋  张庆云  陈烈庭 《大气科学》2006,30(6):1189-1197

利用1961～2000年中国台站降水资料、 NCEP/NCAR再分析资料以及扩展重建海平面温度 (Extended Reconstructed Sea Surface Temperatures, ERSST) 资料, 采用EOF、小波变换、合成及相关方法探讨中国东部梅雨期降水的时空变化及其环流、水汽输送和海温异常特征.分析指出中国东部梅雨期 (6月11日～7月10日) 降水存在三种主要空间型: 江南北部多雨型、长江流域多雨型和江淮平原多雨型.三种降水型都存在多时间尺度特征, 由于年际和年代际振荡的周期和强度随时间的变化有不同表现, 三种雨型旱涝年出现的年份有所不同.三种雨型对应的东亚夏季风环流各子系统的强度、位置、水汽输送等也存在明显差异.梅雨期三种雨型与冬季海温的研究表明:赤道东太平洋海温偏高有利于出现江南北部降水型; 赤道印度洋、南海和西太平洋黑潮海温偏高有利于出现长江流域降水型; 北太平洋中纬度海温偏高则有利于出现江淮平原降水型.  相似文献   

Mechanical compression release device in steel bracing system for retrofitting RC frames     

H. Ghaffarzadeh M.R. Maheri 《地震工程与工程振动(英文版)》2006,5(1):151-158

1 Introduction Braced steel frames are commonly used to resist seismic loads. Their seismic behavior was extensively studied during the past decades (Bertero et al.., 1989; Roeder, 1989; Jain, 1978). Their design is governed by the buckling behavior of the bracing members (ASCE, 1994,2002; CSA, 1994). To prevent or delay the seismic buckling of compressive members in concentrically braced frames in steel structures, a great number of methods have been proposed. These include the use of sp…  相似文献   

Inertial theory of the mean Hadley circulation under the condition of nonstatic equilibrium     

CHAO Jiping  LIU Fei 《中国科学D辑(英文版)》2006,49(5):546-553

1 Introduction The mean meridional circulation plays an important role in the transportation and balance of heat, momen- tum, vortex and vapor between different latitudes. According to the data analysis, there are three circula- tions from the equator to the polar area: the Hadley circulation, a heat-driven circulation which rises around the equator and sinks at a certain latitude; the subpolar circulation, another heat-driven circulation around the polar area; and the Ferrel circulation, an i…  相似文献   

Spatiotemporal analysis of precipitation trends in the Yangtze River catchment   总被引：2，自引：2，他引：2  

Stefan Becker  Marco Gemmer  Tong Jiang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(6):435-444

Precipitation trends in the Yangtze River catchment (PR China) have been analyzed for the past 50 years by applying the Mann-Kendall trend test and geospatial analyses. Monthly precipitation trends of 36 stations have been calculated. Significant positive trends at many stations can be observed for the summer months, which naturally show precipitation maxima. They were preceded and/or followed by negative trends. This observation points towards a concentration of summer precipitation within a shorter period of time. The analysis of a second data set on a gridded basis with 0.5° resolution reveals trends with distinct spatial patterns. The combination of classic trend tests and spatially interpolated precipitation data sets allows the spatiotemporal visualization of detected trends. Months with positive trends emphasize the aggravation of severe situation in a region, which is particularly prone to flood disasters during summer. Reasons for the observed trends were found in variations in the meridional wind pattern at the 850 hPa level, which account for an increased transport of warm moist air to the Yangtze River catchment during the summer months.  相似文献   

Quantifying anthropogenic influence on recent near-surface temperature change   总被引：2，自引：0，他引：2  

M. R. Allen  N. P. Gillett  J. A. Kettleborough  G. Hegerl  R. Schnur  P. A. Stott  G. Boer  C. Covey  T. L. Delworth  G. S. Jones  J. F. B. Mitchell  T. P. Barnett 《Surveys in Geophysics》2006,27(5):491-544

We assess the extent to which observed large-scale changes in near-surface temperatures over the latter half of the twentieth century can be attributed to anthropogenic climate change as simulated by a range of climate models. The hypothesis that observed changes are entirely due to internal climate variability is rejected at a high confidence level independent of the climate model used to simulate either the anthropogenic signal or the internal variability. Where the relevant simulations are available, we also consider the alternative hypothesis that observed changes are due entirely to natural external influences, including solar variability and explosive volcanic activity. We allow for the possibility that feedback processes, other than those simulated by the models considered, may be amplifying the observed response to these natural influences by an unknown amount. Even allowing for this possibility, the hypothesis of no anthropogenic influence can be rejected at the 5% level in almost all cases. The influence of anthropogenic greenhouse gases emerges as a substantial contributor to recent observed climate change, with the estimated trend attributable to greenhouse forcing similar in magnitude to the total observed warming over the 20th century. Much greater uncertainty remains in the response to other external influences on climate, particularly the response to anthropogenic sulphate aerosols and to solar and volcanic forcing. Our results remain dependent on model-simulated signal patterns and internal variability, and would benefit considerably from a wider range of simulations, particularly of the responses to natural external forcing.  相似文献   

Seismogenic destruction of the Kamenka medieval fortress, northern Issyk-Kul region, Tien Shan (Kyrgyzstan)     

Andrey M. Korjenkov  J. Ramon Arrowsmith  Christopher Crosby  Ernes Mamyrov  Lyubov A. Orlova  Irina E. Povolotskaya  Kubatbek Tabaldiev 《Journal of Seismology》2006,10(4):431-442

A paleoseismological study of the medieval Kamenka fortress in the northern part of the Issyk-Kul Lake depression, northern Tien Shan in Kyrgyzstan, revealed an oblique slip thrust fault scarp offsetting the fortification walls. This 700 m long scarp is not related to the 1911 Kebin Earthquake (Ms 8.2) fault scarps which are widespread in the region. As analysis of stratigraphy in a paleoseismic trench and archaeological evidence reveal, it can be assigned to a major twelfth century a.d. earthquake which produced up to 4 m of oblique slip thrusting antithetic to that of the nearby dominant faults. The inferred surface rupturing earthquake apparently caused the fortress destruction and was likely the primary reason for its abandonment, not the Mongolian–Tatar invasions as previously thought.  相似文献   

Climate change and North Sea storm surge extremes: an ensemble study of storm surge extremes expected in a changed climate projected by four different regional climate models   总被引：5，自引：0，他引：5  

Katja Woth  Ralf Weisse  Hans von Storch 《Ocean Dynamics》2006,56(1):3-15

The coastal zones are facing the prospect of changing storm surge statistics due to anthropogenic climate change. In the present study, we examine these prospects for the North Sea based on numerical modelling. The main tool is the barotropic tide-surge model TRIMGEO (Tidal Residual and Intertidal Mudflat Model) to derive storm surge climate and extremes from atmospheric conditions. The analysis is carried out by using an ensemble of four 30-year atmospheric regional simulations under present-day and possible future-enhanced greenhouse gas conditions. The atmospheric regional simulations were prepared within the EU project PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects). The research strategy of PRUDENCE is to compare simulations of different regional models driven by the same global control and climate change simulations. These global conditions, representative for 1961–1990 and 2071–2100 were prepared by the Hadley Center based on the IPCC A2 SRES scenario. The results suggest that under future climatic conditions, storm surge extremes may increase along the North Sea coast towards the end of this century. Based on a comparison between the results of the different ensemble members as well as on the variability estimated from a high-resolution storm surge reconstruction of the recent decades it is found that this increase is significantly different from zero at the 95% confidence level for most of the North Sea coast. An exception represents the East coast of the UK which is not affected by this increase of storm surge extremes.  相似文献   

Brest sea level record: a time series construction back to the early eighteenth century     

Guy Wöppelmann  Nicolas Pouvreau  Bernard Simon 《Ocean Dynamics》2006,56(5-6):487-497

The completeness and the accuracy of the Brest sea level time series dating from 1807 make it suitable for long-term sea level trend studies. New data sets were recently discovered in the form of handwritten tabulations, including several decades of the eighteenth century. Sea level observations have been made in Brest since 1679. This paper presents the historical data sets which have been assembled so far. These data sets span approximately 300 years and together constitute the longest, near-continuous set of sea level information in France. However, an important question arises: Can we relate the past and the present-day records? We partially provide an answer to this question by analysing the documents of several historical libraries with the tidal data using a ‘data archaeology’ approach advocated by Woodworth (Geophys Res Lett 26:1589–1592, 1999b). A second question arises concerning the accuracy of such records. Careful editing was undertaken by examining the residuals between tidal predictions and observations. It proved useful to remove the worst effects of timing errors, in particular the sundial correction to be applied prior to August 1, 1714. A refined correction based on sundial literature [Savoie, La gnomique, Editions Les Belles Lettres, Paris, 2001] is proposed, which eliminates the systematic offsets seen in the discrepancies in timing of the sea level measurements. The tidal analysis has also shown that shallow-water tidal harmonics at Brest causes a systematic difference of 0.023 m between mean sea level (MSL) and mean tide level (MTL). Thus, MTL should not be mixed with the time series of MSL because of this systematic offset. The study of the trends in MTL and MSL however indicates that MTL can be used as a proxy for MSL. Three linear trend periods are distinguished in the Brest MTL time series over the period 1807–2004. Our results support the recent findings of Holgate and Woodworth (Geophys Res Lett) of an enhanced coastal sea level rise during the last decade compared to the global estimations of about 1.8 mm/year over longer periods (Douglas, J Geophys Res 96:6981–6992, 1991). The onset of the relatively large global sea level trends observed in the twentieth century is an important question in the science of climate change. Our findings point out to an ‘inflexion point’ at around 1890, which is remarkably close to that in 1880 found in the Liverpool record by Woodworth (Geophys Res Lett 26:1589–1592, 1999b).  相似文献   

Surface and Upper Air Fields During Extreme Winter Precipitation Over the Western Himalayas     

A. P. Dimri 《Pure and Applied Geophysics》2006,163(8):1679-1698

Surface and upper air circulation features associated with extreme precipitation years are demonstrated during winter season viz., December, January, February and March (DJFM) to examine winter weather affecting the western Himalayas. These circulations are studied over the domain 15°S–45°N and 30°E–120°E. This domain is considered particularly to illustrate the distribution of precipitation due to a wintertime eastward moving synoptic weather system called western disturbances. Surplus and deficient years of seasonal (DJFM) precipitation are identified using ± 20% departure from mean from uninitialized daily reanalysis data of forty (1958–1997) years of the National Center For Environmental Prediction (NCEP), US. The years 1965–1969, 1973 and 1991 are found to be surplus years and the years 1962, 1963, 1971, 1977, and 1985 are found to be deficient years. Comparative study between composites of these two categories is made using students t-test of significance. Significant differences in sea-level pressure, zonal and meridional component of wind at surface and upper levels, total precipitable water content, geopotential height and temperature are observed in the two contrasting seasons.  相似文献