夏季青藏高原东部降水变化与副热带高压带活动的研究

用青藏高原上常规的台站资料和NCEP/NCAR的再分析资料,分析和研究了1993/1994年夏季5—8月青藏高原东部降水变化与西太平洋副热带高压南北移动的关系。结果表明:1993年夏季的副热带高压异常偏南,5—8月副高脊线北移过程中,还伴有准双周南北移动过程;而1994年夏季的副热带高压异常偏北,5—8月副高脊线北移过程中,则主要伴有30—60d的低频变化的南北移动过程。同时,在分析青藏高原上的天气变化特征时,发现这两年高原东部的降水变化特征也有明显的不同,夏季高原上降水的活跃和中断与副高脊线南北移动变化有类似的特征。因此,夏季西太平洋副热带高压南北移动可能与高原东部降水的中断/活跃有一定的关系。     

基于双多普勒雷达及闪电资料分析一次强降水过程

为进一步了解多普勒雷达及闪电资料在中小尺度天气系统方面的应用以及降水系统动力结构的研究,利用合肥和阜阳两部S波段多普勒雷达资料,通过两步变分反演法反演双雷达,并采用模糊逻辑算法进行云类型识别,再结合垂直累计液态水含量VIL、降水和闪电分布特征,分析了2010年6月7-10日发生在安徽合肥和阜阳的一次持续性强降水过程。结果表明:此次持续性强降水过程与风场的低层辐合和高层辐散、风场的气旋性旋转以及水平风切变相关;此次降水过程是以层状云降水为主的积云混合云降水;另外,以降水为主的层状云,其闪电频数低且以负闪为主,闪电之后20 min左右出现强降水;此次暴雨的VIL值不是很大,强降水区对应的VIL值基本3 kg·m-2;云识别结果、降水区、VIL值与雷达回波强度之间的对应关系较好。     

近40年中国区域的气候型变化与北半球大气环流特征10年际时空变化的关系

根据１８００－１９８９年（１１０年）的资料，分析研究了新加坡地区月平均和年平均降雨量的一些特征。主要结论是：新加坡年平均降雨量存在准２－６年和１８年的周期振荡；亚洲季风以及ＥＮＳＯ对新加坡降雨量有明显的影响。新加坡年雨量的谷值出现在西南季风期而峰值在东北季风期。在Ｅｌ Ｎｉｎｏ年，新加坡降雨量多为负距平；而在反Ｅｌ Ｎｉｎｏ年，新加坡降雨量多为正距平。     

An analysis of storm-induced landslides in colluvial soils overlying mudrock sequences, southeastern Ohio, USA

In late-June, 1998, a series of thunderstorms dropped 16.5 cm (6.5 in.) of rain in a 72-h period over southeastern Ohio, causing extensive flooding, six deaths, and 179 million dollars in property damage. The storms also triggered more than 60 shallow landslides along a 64 km (40-mi) stretch of Interstate 77 between Buffalo and Marietta, Ohio. Almost all of the landslides were translational, occurring along the contact between colluvial soils and the underlying bedrock (shales, claystones, mudstones). Six sites were selected in the affected area for a detailed study of the shallow landslides. At each site, a record was made of the stratigraphy, slope geometry, number of landslides, landslide dimensions, hydrologic conditions, and influence of vegetation on landslide distribution. Both colluvial soils and underlying bedrock were sampled for laboratory investigations, which included determination of natural water content, grain size distribution, Atterberg limits, permeability, slake durability, and shear-strength parameters. Data from laboratory tests were used to perform sensitivity and stability analyses with respect to varying slope angles, strength parameters, and thicknesses of saturated colluvial soil. The results of the study indicate that the shallow landslides along Interstate 77 occurred when the colluvial soils reached 90% to 100% saturation, depending upon the slope angles.     

Pathogenic fungi: an unacknowledged risk at coastal resorts? New insights on microbiological sand quality in Portugal

Whilst the potential impact on beach users from microorganisms in water has received considerable attention, there has been relatively little investigation into microbial contaminants in sand. Thirty three beaches across Portugal were analyzed during a five year period (2006-2010) to determine the presence of yeasts, pathogenic fungi, dermatophytes, total coliforms, Escherichia coli and intestinal enterococci in sand.Our results showed that 60.4% of the samples were positive for fungi and that 25.2% were positive for the bacterial parameters. The most frequent fungal species found were Candida sp. and Aspergillus sp., whereas intestinal enterococci were the most frequently isolated bacteria. Positive associations were detected among analyzed parameters and country-regions but none among those parameters and sampling period.Regarding threshold values, we propose 15 cfu/g for yeasts, 17 cfu/g for potential pathogenic fungi, 8 cfu/g for dermatophytes. Eighty four cfu/g for coliforms, 250 cfu/g for E. coli, and 100 cfu/g for intestinal enterococci.     

祁连山空中云水资源开发潜力研究新进展

祁连山及河西走廊地区是我国气候变化敏感区和生态脆弱区。本文通过对2005a以来祁连山云水资源相关最新研究成果的总结,旨在揭示气候变暖对祁连山云水资源影响包括气候变化、水汽时空变化、地形云特征的基础上,分析评估了祁连山云水资源开发潜力及效益。实验研究表明,在祁连山区开展人工增雨(雪)作业,每年可增加降水量3.7×10_⁸～７.4×10_⁸m_³。近10年来,甘肃春季飞机人工增雨作业年均增加降水量为13.5×10_⁸m_³,平均投入产出比为1:30。     

有限区域流函数和速度势的3种求解方法在分析台风Bilis暴雨增幅中的比较研究

将有限区域流函数、速度势求解中常用的两种张驰法(即理查逊法和加速利布曼法)与调和—余弦谱展开法(H-C法)进行了比较,理论研究表明:H-C法单独考虑边界影响分量,物理意义明确,且不会丢失边界上的天气系统;从计算上看,H-C法重建的风场能精确还原原始风场,且计算效率明显高于两种张驰法,即收敛更快。通过在台风Bilis(0604)暴雨增幅过程诊断中的应用发现,常用的两种张驰迭代方法在求解有限区域流函数和速度势的问题上效果都不是很好,即:用理查逊法和加速利布曼法计算的流函数和速度势重建的风场与原始风场差别较大,不能准确还原原始风场;用H-C法不仅计算效率高,还原的风场与原始风场差异极小,且不受南边界较强的西南季风涌影响,在暴雨增幅前期能较好地反映与暴雨增幅相关的强辐合信号。因此,可用H-C法计算得到的无辐散风和无旋风对有限区域的天气系统进行更深入的动力结构分析。     

Late Holocene climates of the Near East deduced from Dead Sea level variations and modern regional winter rainfall

The Dead Sea is a terminal lake of one of the largest hydrological systems in the Levant and may thus be viewed as a large rain gauge for the region. Variations of its level are indicative of the climate variations in the region. Here, we present the decadal- to centennial-resolution Holocene lake-level curve of the Dead Sea. Then we determine the regional hydroclimatology that affected level variations. To achieve this goal we compare modern natural lake-level variations and instrumental rainfall records and quantify the hydrology relative to lake-level rise, fall, or stability. To quantify that relationship under natural conditions, rainfall data pre-dating the artificial Dead Sea level drop since the 1960s are used. In this respect, Jerusalem station offers the longest uninterrupted pre-1960s rainfall record and Jerusalem rains serve as an adequate proxy for the Dead Sea headwaters rainfall. Principal component analysis indicates that temporal variations of annual precipitation in all stations in Israel north of the current 200 mm yr⁻¹ average isohyet during 1940–1990 are largely synchronous and in phase (70% of the total variance explained by PC1). This station also represents well northern Jordan and the area all the way to Beirut, Lebanon, especially during extreme drought and wet spells. We (a) determine the modern, and propose the past regional hydrology and Eastern Mediterranean (EM) climatology that affected the severity and length of droughts/wet spells associated with multiyear episodes of Dead Sea level falls/rises and (b) determine that EM cyclone tracks were different in average number and latitude in wet and dry years in Jerusalem. The mean composite sea level pressure and 500-mb height anomalies indicate that the potential causes for wet and dry episodes span the entire EM and are rooted in the larger-scale northern hemisphere atmospheric circulation. We also identified remarkably close association (within radiocarbon resolution) between climatic changes in the Levant, reflected by level changes, and culture shifts in this region.     

开挖与降雨作用下边坡失稳机理及模拟分析

边坡开挖和降雨通常是导致边坡失稳的重要原因。本文以湖南湘西山区某国道扩建开挖边坡为研究对象,基于现场边坡监测结果和数值模拟分析,研究了在边坡开挖和降雨条件下坡体变形位移的过程。结果表明:边坡的破坏是一个渐变的过程,不同的影响因素对边坡的影响不同。开挖切方是浅层坡体失稳的诱发因素,开挖切方破坏了坡体的应力平衡,使坡体的应力重新分布,并在坡体中产生浅层的滑动面。雨水的入渗是坡体深层滑动面的诱发因素,雨水沿着裂缝渗入坡体,使浅部滑动面上下土体的变形差进一步加大,进而产生浅层牵引式滑动破坏。同时雨水的入渗使碎石土和强风化页岩交界附近产生高孔隙水压力,在水-岩土共同作用逐渐形成软化的滑带土,从而形成深层滑动面。     

Analyses of the warm season rainfall climatology of the northeastern US using regional climate model simulations and radar rainfall fields

We examine the warm season (April-September) rainfall climatology of the northeastern US through analyses of high-resolution radar rainfall fields from the Hydro-NEXRAD system and regional climate model simulations using the weather research and forecasting (WRF) model. Analyses center on the 5-year period from 2003 to 2007 and the study area includes the New York-New Jersey metropolitan region covered by radar rainfall fields from the Fort Dix, NJ WSR-88D. The objective of this study is to develop and test tools for examining rainfall climatology, with a special focus on heavy rainfall. An additional emphasis is on rainfall climatology in regions of complex terrain, like the northeastern US, which is characterized by land-water boundaries, large heterogeneity in land use and cover, and mountainous terrain in the western portion of the region. We develop a 5-year record of warm season radar rainfall fields for the study region using the Hydro-NEXRAD system. We perform regional downscaling simulations for the 5-year study period using the WRF model. Radar rainfall fields are used to characterize the interannual, seasonal and diurnal variation of rainfall over the study region and to examine spatial heterogeneity of rainfall. Regional climate model simulations are characterized by a wet bias in the rainfall fields, with the largest bias in the high-elevation regions of the model domain. We show that model simulations capture broad features of the interannual, seasonal, and diurnal variation of rainfall. Model simulations do not capture spatial gradients in radar rainfall fields around the New York metropolitan region and land-water boundaries to the east. The model climatology of convective available potential energy (CAPE) is used to interpret the regional distribution of warm season rainfall and the seasonal and diurnal variability of rainfall. We use hydrologic and meteorological observations from July 2007 to examine the interactions of land surface processes and rainfall from a regional perspective.