The westerly fluctuation and water vapor transport over the Qilian-Heihe valley

The westerly fluctuation and the atmospheric water vapor transport over the Qilian-Heihe valley are analyzed and the results show that, in the water vapor transport stream field from Jun to September, this valley is in the westerly stream and the water vapor comes from westerlies water transport via the Black Sea and the Caspian Sea. The net water vapor transport is less net import and different from most areas of the northwest China. The interannual changes in water vapor transport over the valley arise from the westerly fluctuation, and have a positive relationship to the interannual changes in westerly wind speed. The cold air actions from the Mongol low pressure are the primary system that controls the westerly water vapor transport. Its action chain is that, the Mongol low pressure is strengthened → the circulation meridionality will be increased → the cold air will move southwards → the westerly will be stronger → the wind convergence of direction and speed will be stronger → the water vapor convergence transport will be increased → the local water vapor content will be increased. The interannual changes in atmospheric water vapor transport over the valley rely mainly on the convergence transport, but the effect of advection transport is less. The interannual changes of strong or weak westerly affect mainly the convergence transport, and then make the atmospheric water vapor net transport increase or decrease over the Qilian-Heihe valley.     

2018年台风“摩羯”和“温比亚”路径的影响因子分析

利用中国气象局(CMA)提供的热带气旋最佳路径资料和欧洲中心(ECMWF)提供的ERA interim再分析资料,对2018年两个北上影响山东的台风"摩羯"和"温比亚"路径差异的原因进行分析发现:"摩羯"和"温比亚"台风路径的差异主要与周围天气系统分布差异有关,两台风均先后受到副热带高压和大陆高压的影响,"温比亚"还受高空槽的影响,使其转向角度较大,而台风与高压系统相互作用形成的引导气流是影响这两个台风路径的主要因素。"摩羯"和"温比亚"的最佳引导气流均位于台风中心5个纬度半径内,不同阶段所受引导气流的高度存在差异,台风登陆前中低层引导气流对台风移向的指示作用均优于高层,登陆后转向前纬向引导气流均优于经向,但稳定性稍差,转向后除"温比亚"经向引导气流相关较差外均整层相关较好,中高层略优于低层,且高层风(300～200hPa)可以提前12h预报台风转向。此外,台风总是向着台风附近的正涡度平流方向移动,正涡度平流越强,台风移动越快。     

Segmentation-based approach for trend analysis and structural breaks in rainfall time series (1851–2006) over India

ABSTRACT

This study analysed long-term rainfall data (1851–2006) over seven climatic zones of India at seasonal and annual scales based on three techniques: (i) linear regression, (ii) multifractal detrended fluctuation analysis (MFDFA) and (iii) Bayesian algorithm. The linear regression technique was used for trend analysis of short-term (30 years) and long-term (156 years) rainfall data. The MFDFA revealed small- and large-scale fluctuations, whereas the Bayesian algorithm helped in quantifying the uncertainty in break-point detection from the rainfall time series. Major break points years identified through Bayesian algorithm were 1888, 1904 and 1976. The MFDFA technique identified that high fluctuation years were between 1871–1890, 1891–1910 and 1951–1970. Linear regression-based analysis revealed 1881–1910 and 1971–2006 as break-point periods in the North Mountainous Indian region. A similar analysis was carried out for India as a whole, as well as its seven climatic zones.     

Interdecadal fluctuation of dry and wet climate boundaries in China in the past 50 years

Based on the mean yearly precipitation and the total yearly evaporation data of 295 meteorological stations in China in 1951-1999, the aridity index is calculated in this paper. According to the aridity index, the climatic regions in China are classified into three types, namely, arid region, semi-arid region and humid region. Dry and wet climate boundaries in China fluctuate markedly and differentiate greatly in each region in the past 50 years. The fluctuation amplitudes are 20-400 km in Northeast China, 40-400 km in North China, 30-350 km in the eastern part of Northwest China and 40-370 km in Southwest China. Before the 1980s (including 1980), the climate tended to be dry in Northeast China and North China, to be wet in the eastern part of Northwest China and very wet in Southwest China. Since the 1990s there have been dry signs in Southwest China, the eastern part of Northwest China and North China. The climate becomes wetter in Northeast China. Semi-arid region is the transitional zone between humid and arid regions, the monsoon edge belt in China, and the susceptible region of environmental evolution. At the end of the 1960s dry and wet climate in China witnessed abrupt changes, changing wetness into dryness. Dry and wet climate boundaries show the fluctuation characteristics of the whole shifts and the opposite fluctuations of eastward, westward, southward and northward directions. The fluctuations of climatic boundaries and the dry and wet variations of climate have distinctive interdecadal features.     

海峡西岸一次雾过程微结构及其起伏特征研究

2013年春季在福建省厦门市开展了海雾综合观测,选取了4月17日一次海雾期间的能见度、常规气象要素和雾滴谱资料,分析了沿岸海雾发生时的天气系统和微结构特征,并讨论了气象要素的起伏对雾发展、持续、消散及其微结构起伏的影响。海雾间歇阶段和消散阶段均有风速风向的突变;含水量、数浓度、平均直径和最大直径在不同阶段均有明显的差异,即使在同一阶段也不断波动;海雾爆发性增强过程中雾滴谱出现爆发性拓宽,平均直径、数密度和含水量骤然增大,宏观的气象条件也发生了明显变化;海雾不同阶段由于湍流、辐射以及气象条件的差异,雾滴空间分布的不连续,雾滴核化、凝结、碰并和蒸发作用,微结构的起伏较大。      

Effect of earthquake‐induced axial load fluctuations on asymmetric frame–wall–rocking foundation systems

Fluctuations in axial load imposed on a rocking footing will affect its moment capacity, the shape of its moment–rotation hysteresis, and potentially the system's seismic performance. Structural asymmetry increases the likelihood of axial load variation during earthquake excitations. To investigate this issue, a unique centrifuge testing program was carried out on low‐rise frame–wall–rocking foundation systems. In this paper, the seismic behaviors of asymmetric and symmetric models from this test program are systematically compared. Experimental results reveal that placing the lateral force resisting shear wall outboard produces significant axial load fluctuation, which in turn greatly deteriorate the lateral load‐carrying capacity of a foundation rocking dominated frame–wall system, particularly in its weak direction. However, it strengthens the system when loading is towards the shear wall, leading to a highly asymmetric hysteretic response. During earthquake loading, all asymmetric rocking foundation systems observe smaller peak roof accelerations, but larger peak and permanent roof drifts compared with the symmetric systems. Despite these differences in response, the axial load fluctuation and structural asymmetry do not significantly change the relative energy dissipated by the rocking foundations and inelastic structural components within each frame–wall–rocking foundation model. Copyright © 2015 John Wiley & Sons, Ltd.     

水位波动下非饱和心墙土坝体的渗流和稳定性

基于Richards方程,对坝体的饱和-非饱和渗流场进行了模拟,再根据饱和-非饱和渗流场和非饱和土抗剪强度公式,对坝体的稳定性进行了分析。结果表明,水位骤降过程中坝体的安全系数通常呈现先缓慢增加后迅速减小的变化过程,分析坝体失稳时塑性区和位移场发现,水位下降的初期,坝体左侧坡体的安全系数要低于坝体右侧坡体,但水位下降到一定程度,右侧坡体的安全系数迅速减小,并先于左侧坡体失稳;采用有限元强度折减法用于多坡面边坡稳定分析时,只能获得最小安全系数的包络线;心墙具有隔水防渗的作用,对水位变化渗流具有阻尼作用。     

半隐蔽式草方格沙障凹曲面形成的流场解析及沉积表征

利用野外风沙观测、沉积物粒度分析和等比例实体草方格风洞流场模拟,解析了草方格沙障内部凹曲面形成的风沙流场过程。草方格分别作为疏透沙障和地表粗糙元对贴地层和近地层风沙流具有不同的影响：床面蚀、积分布和方格中心凹曲面的形成发展,以及沉积物粒度变化,取决于草带之间的贴地层流场分布格局以及草带对风沙流中固体物质的截留;近地层风力普遍受到草方格粗糙元的削弱,促进了沙面稳定。高风速下输沙率垂向分布的“象鼻”结构,体现了草方格对促使风沙流结构变异、形成和维持草方格凹曲面的重要性。沙丘不同部位草方格沉积物粒度分布模式不同,显示沙丘部位也是影响草方格内部流场的一个因素,以迎风坡中部最有利于方格内凹曲面的形成。     

Preliminary analysis of spatiotemporal pattern of global land surface water

Land surface water (LSW) is one of the most important resources for human survival and development, and it is also a main component of global water recycling. A full understanding of the spatial distribution of land surface water and a continuous measuring of its dynamics can support to diagnose the global ecosystem and environment. Based on the Global Land 30-water 2000 and Global Land 30-water 2010 products, this research analyzed the spatial distribution pattern and temporal fluctuation of land surface water under scale-levels of global, latitude and longitude, continents, and climate zones. The Global Land 30-water products were corrected the temporal inconsistency of original remotely sensed data using MODIS time-series data, and then calculated the indices such as water area, water ration and coefficient of spatial variation for further analysis. Results show that total water area of land surface is about 3.68 million km² (2010), and occupies 2.73% of land area. The spatial distribution of land surface water is extremely uneven and is gathered mainly in mid- to high-latitude area of the Northern Hemisphere and tropic area. The comparison of water ratio between 2000 and 2010 indicates the overall fluctuation is small but spatially differentiated. The Global Land 30-water products and the statistics provided the fundamental information for analyzing the spatial distribution pattern and temporal fluctuation of land surface water and diagnosing the global ecosystem and environment.     

Climate change regionalization in China(1961–2010)

Since climatic condition is the important foundation for human subsistence and development and the key factor in sustainable development of economy and society, climate change has been a global issue attracting great attentions of politicians, scientists, governments, and the public alike throughout the world. Existing climate regionalization in China aims to characterize the regional differences in climate based on years of the mean value of different climate indexes. However, with the accelerating climate change nowadays, existing climate regionalization cannot represent the regional difference of climate change, nor can it reflect the disasters and environmental risks incurred from climate changes. This paper utilizes the tendency value and fluctuation value of temperature and precipitation from 1961 to 2010 to identify the climate change quantitatively, and completes the climate change regionalization in China(1961–2010) with county administrative regionalization as the unit in combination with China's terrain feature. Level-I regionalization divides China's climate change(1961–2010) into five tendency zones based on the tendency of temperature and precipitation, which are respectively Northeast China-North China warm-dry trend zone, East China-Central China wet-warm trend zone, Southwest China-South China dry-warm trend zone, Southeast Tibet-Southwest China wet-warm trend zone, and Northwest China-Qinghai-Tibet Plateau warm-wet trend zone; level-II regionalization refers to fourteen fluctuation regions based on level-I regionalization according to the fluctuation of temperature and precipitation.