2003年7月上旬张家界特大暴雨山洪分析   总被引：7，自引：4，他引：7  

周雨华  黄培斌  刘兵  张海  黄小玉  丁小剑 《气象》2004,30(10):38-42

对造成 2 0 0 3年 7月 8～ 1 0日张家界特大暴雨山洪的主要影响系统、物理量诊断场资料、多普勒雷达回波资料及自动气象站要素进行了分析 ,并重点分析了张家界特定的地形条件对降水的增幅作用及暴雨的夜发特征 ,为湘西北的暴雨山洪预报提供了一些有益的启示。  相似文献   

近30年夏季亚欧大陆中高纬度阻塞高压的统计特征   总被引：10，自引：0，他引：10  

李峰  丁一汇 《气象学报》2004,62(3):347-354

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.  相似文献   

BECAPEX科学试验城市建筑群落边界层大气环境特征及其影响   总被引：9，自引：1，他引：9  

徐祥德  丁国安  卞林根  谢立安 《气象学报》2004,62(5):663-671

20 0 1～ 2 0 0 3年在北京实施了大气边界层动力、热力、化学综合观测试验 (BECAPEX ,BeijingCityAtmosphericPollutionObservationFieldExperiment) ,获取了北京城市大气动力和大气化学三维结构图像。综合观测试验分析研究发现 ,城市区域呈非均匀次生尺度热岛分布 ,并伴随着城市次生尺度环流 ,影响了局地空气污染物分布特征。MODIS卫星遥感 地面观测资料经过变分分析 ,可发现北京城市空气污染与周边区域影响源有密切关系 ,并影响城市群落环境气候特征 ,导致该区域日照、雾日、低云量和能见度呈显著年代际变化趋势。  相似文献   

REE and (э)Nd of clay fractions in sediments from the eastern Pacific Ocean: Evidence for clay sources     

LIU Jihua  SHI Xuefa  Chen Lirong  HUANG Yongyang  Wang Yinxi  Cui Yingchun  BU Wenrui 《中国科学D辑(英文版)》2005,48(5)

Clay fractions in the non-calcareous surface sediments from the eastern Pacific were analyzed for clay minerals, REE and 143Nd/144Nd. Montmorillonite/illite ratio (M/I ratio), total REE contents ((REE), LREE/HREE ratio and cerium anomaly (бCe) may effectively indicate the genesis of clay minerals. Clay fractions with M/I ratio >1, бCe (0.85, (REE (400 μg/g, LREE/HREE ratio (4, and REE patterns similar to those of pelagic sediments are terrigenous and autogenetic mixed clay fractions and contain more autogenetic montmorillonite. Clay fractions with M/I ratio <1, бCe=0.86 to 1.5, ΣREE=200 to 350 μg/g, LREE/HREE ratio (6 and REE distribution patterns similar to that of China loess are identified as terrigenous clay fraction. The 143Nd/144Nd ratios or (э)Nd values of clay fractions inherit the features of terrigenous sources of clay minerals. Clay fractions are divided into 4 types according to (э)Nd values. Terrigenous clay minerals of type I with the (э)Nd values of -8 to -6 originate mainly from North American fluvial deposits. Those of type II with the (э)Nd values of -9 to -7 are mainly from the East Asia and North American fluvial deposits. Those of type III with (э)Nd values of -6 to -3 could come from the central and eastern Pacific volcanic islands. Those of type IV with (э)Nd values of -13 to -12 may be from East Asia eolian. The terrigenous and autogenetic mixed clay fractions show patchy distributions, indicating that there are volcanic or hot-spot activities in the eastern Pacific plate, while the terrigenous clay fractions cover a large part of the study area, proving that the terrigenous clay minerals are dominant in the eastern Pacific.  相似文献   

“雪龙号”2003北极航次气相多环芳烃纬度分布观测          下载免费PDF全文

丁翔  谢周清  向彩红  麦碧娴  王新明  孙立广  盛国英  傅家谟 《极地研究》2005,17(4):272-278

2003年“雪龙号”北极科学考察期间,对沿途海洋大气进行采样,分析其中气相多环芳烃的空间分布。结果显示,气相中主要是2-4环的多环芳烃,其中菲为主要的化合物,平均占到总多环芳烃的55.1%。在整个航程的广泛区域尺度内,气相总多环芳烃浓度在1043.9-92993.1pg/m3。空间分布上,远东亚的海面>北太平洋海面>北极圈以内海面;总多环芳烃的浓度随纬度升高呈现显著降低的趋势。通过Clausius-Clapeyron方程对浓度和温度相互关系的分析表明,温度是控制气相多环芳烃长距离传输的主要因素。  相似文献   

The effect of conservation practices in sloped croplands on soil hydraulic properties and root‐zone moisture dynamics          下载免费PDF全文

Lirong Lin  Jiazhou Chen 《水文研究》2015,29(9):2079-2088

Rain‐induced erosion and short‐term drought are the two factors that limit the productivity of croplands in the red soil region of subtropical China. The objective of this study was to estimate the effects of conservation practices on hydraulic properties and root‐zone water dynamics of the soil. A 3‐year experiment was performed on a slope at Xianning. Four treatments were evaluated for their ability to reduce soil erosion and improve soil water conditions. Compared with no practices (CK) and living grass strips (GS), the application of polyacrylamide (PAM) significantly reduced soil crust formation during intense rainfall, whereas rice straw mulching (SM) completely abolished soil crust formation. The SM and PAM treatments improved soil water‐stable aggregates, with a redistribution of micro‐aggregates into macro‐aggregates. PAM and SM significantly increased the soil water‐holding capacity. These practices mitigated the degradation of the soil saturated hydraulic conductivity (Ks) during intense rainfalls. These methods increased soil water storage but with limited effects during heavy rainfalls in the wet period. In contrast, during the dry period, SM had the highest soil water storage, followed by PAM and CK. Grass strips had the lowest soil water storage because of the water uptake during the vigorous grass growth. A slight decline in the soil moisture resulted in a significant decrease in the unsaturated hydraulic conductivity (Ku) of the topsoil. Therefore, the hydraulic conductivity in the field is governed by soil moisture, and the remaining soil moisture is more important than improving soil properties to resist short‐term droughts. As a result, SM is the most effective management practice when compared with PAM and GS, although they all protect the soil hydraulic properties during wet periods. These results suggest that mulching is the best strategy for water management in erosion‐threatened and drought‐threatened red soils. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Vertical vibration of a rigid strip footing on viscoelastic half-space     

Changjie Zheng  Lubao Luan  George Kouretzis  Xuanming Ding 《国际地质力学数值与分析法杂志》2020,44(14):1983-1995

This paper presents an analytical method for modeling the dynamic response of a rigid strip footing subjected to vertical-only loads. The footing is assumed to rest on the surface of a viscoelastic half-space; therefore, effects of hysteretic soil damping on the impedance of the foundation and the generated ground vibrations are considered in the solution. To solve the mixed boundary value problem, we use the Fourier transform to cast a pair of dual integral equations providing contact stresses, which are solved by means of Jacobi orthogonal polynomials. The resulting soil and footing displacements and stresses are obtained by means of the Fourier inverse transform. The solution provides more realistic estimates of footing impedance, compared to existing solutions for elastic soil, as well as of the attenuation of ground vibrations with distance of the footing. The latter is important for the estimation of machine vibration effects on nearby structures and installations.  相似文献   

Remote estimation of terrestrial evapotranspiration by Landsat 5 TM and the SEBAL model in cold and high‐altitude regions: a case study of the upper reach of the Shule River Basin,China          下载免费PDF全文

Yaping Chang  Yongjian Ding  Qiudong Zhao  Shiqiang Zhang 《水文研究》2017,31(3):514-524

Evapotranspiration (ET) is an important expenditure in water and energy balances, especially on cold and high‐altitude land surfaces. Daily ET of the upper reach of the Shule River Basin was estimated using Landsat 5 TM data and the Surface Energy Balance Algorithm for Land (SEBAL) model. Based on observations made at the Suli station, the algorithms of land surface temperature and soil heat flux in SEBAL were modified. Land surface temperature was retrieved and compared with ground truth via three methods: the radiative transfer equation method, the mono‐window algorithm, and the single‐channel method. We selected the best of these methods, mono‐window algorithm, for estimating ET. The average error of daily ET estimated by the modified SEBAL model and measured by the eddy covariance system was 16.4%, with a root‐mean‐square error of 0.52 mm d^?1. The estimated ET means were 3.09, 2.48, and 1.48 mm d^?1 on June 9 (DOY 160), June 25 (DOY 176), and July 27 (DOY 208) of the year 2010, respectively. The average estimated ET on the glacier surface of all days was more than 3 mm d^?1, a measurement that is difficult to capture in‐situ and has rarely been reported. This study will improve the understanding of water balance in cold, high‐altitude regions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Torsional dynamic response of a large‐diameter pipe pile in viscoelastic saturated soil     

Changjie Zheng  Hanlong Liu  Xuanming Ding  Yaru Lv 《国际地质力学数值与分析法杂志》2014,38(16):1724-1743

An analytical solution is developed in this paper to investigate the dynamic response of a large‐diameter end‐bearing pipe pile subjected to torsional loading in viscoelastic saturated soil. The wave propagation in saturated soil and pile are simulated by Biot's two‐phased linear theory and one‐dimensional elastic theory, respectively. The dynamic equilibrium equations of the outer soil, inner soil, and pile are established. The solutions for the outer and inner soils in frequency domain are obtained by Laplace transform technique and the separation of variables method. Then, the dynamic response of the pile is obtained on the basis of the perfect contacts between the pile and the outer soil as well as the inner soil. The results in this paper are compared with that of a solid pile in elastic saturated soil to verify the validity of the solution. Furthermore, the solution in this paper is compared with the classic plane strain solution to verify the solution further and check the accuracy of the plane strain solution. Numerical results are presented to analyze the vibration characteristics and illustrate the effect of the soil parameters and the geometry size of the pile on the complex impedance and velocity admittance of the pile head. Finally, the displacement of the soil at different depth and frequency is analyzed. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Estimation of instantaneous peak flow from maximum mean daily flow by regionalization of catchment model parameters          下载免费PDF全文

Jie Ding  Uwe Haberlandt 《水文研究》2017,31(3):612-626

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