Impact of satellite soundings on the simulation of heavy rainfall associated with tropical depressions

The present study is carried out to examine the impact of temperature and humidity profiles from moderate resolution imaging spectroradiometer (MODIS) or/and atmospheric infrared sounder (AIRS) on the numerical simulation of heavy rainfall events over the India. The Pennsylvania State University–National Centre for Atmospheric Research fifth-generation mesoscale model (MM5) and its three-dimensional variational (3D-Var) assimilation technique is used for the numerical simulations. The heavy rainfall events occurred during October 26–29, 2005, and October 27–30, 2006, were chosen for the numerical simulations. The results showed that there were large differences observed in the initial meteorological fields from control experiment (CNT; without satellite data) and assimilation experiments (MODIS (assimilating MODIS data), AIRS; (assimilating AIRS data); BOTH (assimilating MODIS and AIRS data together)). The assimilation of satellite data (MODIS, AIRS, and BOTH) improved the predicted thermal and moisture structure of the atmosphere when compared to CNT. Among the experiments, the predicted track of tropical depressions from MODIS was closer to the observed track. Assimilation of MODIS data also showed positive impact on the spatial distribution and intensity of predicted rainfall associated with the depressions. The statistical skill scores obtained for different experiments showed that assimilation of satellite data (MODIS, AIRS, and BOTH) improved the rainfall prediction skill when compared to CNT. Root mean square error in quantitative rainfall prediction is less in the experiment which assimilated MODIS data when compared to other experiments.     

考虑气压势影响的降雨入渗数值模拟研究

利用一维下渗模型的数值模拟方法研究下渗试验过程中气压势与饱和水力传导度K_s的关系。数值分析表明,可通过由下渗过程中表层湿润的饱和度来折减K_s值的途径考虑气压势的影响,从而改进计算方法。下渗试验的模拟计算结果表明,改进后的方法比常用的方法有更高的精度。     

A Hybrid Multistage Model of Evolution of the Western Ghats at the Passive Western Continental Margin of India

The Western Ghats (WG) is one of the Great Escarpments of the world that developed and persisted for the last ~60 Ma at the passive Western Continental Margin of India (WCMI). Like many such escarpments, the origin and persistence of the WG cannot be explained by a single mechanism, either lithosphere-asthenosphere or surficial processes, and hence, these are debated. Here I suggest a unified multistage model for the evolution of WG based on the available geophysical and geological data, and link its origin and persistence through possible underplating and detachmentcontrolled mid-crustal ductile flow with the characteristics of the Deccan plateau and the offshore region. The implications of the model for lithosphere-asthenosphere dynamics of the Deccan plateau and Stable Continental Region (SCR) seismicity are discussed.     

城市固体废弃物填埋场表层土壤的降雨入渗规律研究

考虑到黄土地区气候特征和地下水的埋藏深度,城市固体废弃物填埋后,其淋洗液主要是以雨水入渗而产生,则上覆土层的厚度应该根据降雨入渗的深度而确定;根据土壤物理学和饱和-非饱和渗流理论,利用土体颗粒分析试验,求得土水特征曲线以及渗透曲线;通过有限元数值模拟,可得各种降雨条件下的水分入渗规律,为填埋场的顶层设计与淋洗液的溶质运移提供参考与依据。     

Stability investigation of hill cut soil slopes along National highway 222 at Malshej Ghat,Maharashtra

The section of about 12 km of National highway 222 passing through the Malshej Ghat experience frequent slope failure due to complex geological condition, heavy rainfall and slope geometry. The area is part of Western Ghat Deccan trap and slope masses are made of basalt and its weathered crust (debris/soil). The soil slope failure problem mainly occur in rainy seasons due to induced pore water pressure and reduced strength of the slope mass. The present study has been carried out to investigate the slope forming material and assess the stability of soil slopes by numerical approach. For the identification of the vulnerable zones, field study has been carried out and five vulnerable soil slopes identified namely MGS1, MGS2, MGS3, MGS4 and MGS5 on the basis of degree of weathering and slope geometry. The laboratory experiments were carried out to determine the strength properties of the geomaterials. All the input variables acquired from the field and laboratory experiments have been used for numerical simulation, which was performed with the help of limit equilibrium method (LEM) and finite element method (FEM). Numerical analysis provides understanding of the slope behaviour and illustrates that MGS1 and MGS3 are stable slopes, MGS2 and MGS4 are critically stable, whereas, slope MGS5 is unstable. This study recommend the protection of soil slopes and suggest that more detailed investigation is required for long term remedial measures to prevent risk of damage in Malshej Ghat.     

1961-2016年四川地区不同量级不同持续时间降水的 时空特征分析

利用四川地区122站逐日降水数据,采用均值、气候趋势系数等统计方法,对1961-2016年不同量级不同持续时间降水的空间和时间变化特征进行了分析,结果表明：盆地和攀西地区小雨、中雨、大雨和总暴雨所占年降水量比例接近,高原地区小雨降水量约占50%以上,中雨约40%,大雨约10%;整个四川地区小雨日数占总降水日数75%以上,量级越高降水日数越少。年降水量在盆地和攀西地区为减少趋势,高原则相反,年降水日数除了在高原局部微弱增加外其他地区皆减少且大部分区域减少趋势通过99%的显著性水平检验,这种趋势显著性主要体现在小雨量级降水。随着降水量级的增加,高原、盆地东北、攀西和盆地东南的部分地区出现了降水量和降水次数增加趋势,这可能说明高原地区年降水量的增加由小雨量级降水效率以及中雨和大雨降水次数增加导致,盆地和攀西部分地区年降水量的增加主要由降水量级大的降水次数增加导致。     

Impact of vegetation on the simulation of seasonal monsoon rainfall over the Indian subcontinent using a regional model

The change in the type of vegetation fraction can induce major changes in the local effects such as local evaporation, surface radiation, etc., that in turn induces changes in the model simulated outputs. The present study deals with the effects of vegetation in climate modeling over the Indian region using the MM5 mesoscale model. The main objective of the present study is to investigate the impact of vegetation dataset derived from SPOT satellite by ISRO (Indian Space Research Organization) versus that of USGS (United States Geological Survey) vegetation dataset on the simulation of the Indian summer monsoon. The present study has been conducted for five monsoon seasons (1998–2002), giving emphasis over the two contrasting southwest monsoon seasons of 1998 (normal) and 2002 (deficient). The study reveals mixed results on the impact of vegetation datasets generated by ISRO and USGS on the simulations of the monsoon. Results indicate that the ISRO data has a positive impact on the simulations of the monsoon over northeastern India and along the western coast. The MM5-USGS has greater tendency of overestimation of rainfall. It has higher standard deviation indicating that it induces a dispersive effect on the rainfall simulation. Among the five years of study, it is seen that the RMSE of July and JJAS (June–July–August–September) for All India Rainfall is mostly lower for MM5-ISRO. Also, the bias of July and JJAS rainfall is mostly closer to unity for MM5-ISRO. The wind fields at 850 hPa and 200 hPa are also better simulated by MM5 using ISRO vegetation. The synoptic features like Somali jet and Tibetan anticyclone are simulated closer to the verification analysis by ISRO vegetation. The 2 m air temperature is also better simulated by ISRO vegetation over the northeastern India, showing greater spatial variability over the region. However, the JJAS total rainfall over north India and Deccan coast is better simulated using the USGS vegetation. Sensible heat flux over north-west India is also better simulated by MM5-USGS.     

表层岩溶裂隙带土壤地表流失/地下漏失室内模拟实验

以表层岩溶裂隙带为研究对象,采用室内模拟降雨的方法,通过控制降雨强度、坡度、裂隙宽度、裂隙产状,研究其对土壤地表流失、地下漏失的影响。结果表明：（1）土壤地表流失主要受降雨强度和坡度的影响,土壤地表流失量随降雨强度的增大而增大、随坡度的增大而增大,30°坡面土壤地表流失量最高。（2）土壤地下漏失主要受裂隙宽度、产状和坡度的影响,对降雨强度的响应不明显;土壤地下漏失量与裂隙宽度大小呈正相关关系,裂隙走向与坡面走向呈30°时最容易发生土壤地下漏失;坡度与土壤地下漏失的发生呈负相关关系;伴随降雨,土壤地下漏失速率变化幅度较大,漏失速率先增加后减小直至停止。无落水洞、漏斗等管道的岩溶坡面土壤流失的主要形式是地表流失,而土壤地下漏失的主要通道是落水洞、漏斗等大型岩溶管道,土壤地下漏失对土壤流失的总贡献率小于5%。     

柱状危岩体崩塌产生涌浪的物理试验与数值模拟分析

柱状危岩体是三峡库区常见的一种典型地质灾害隐患,其崩塌产生涌浪给库区航运、旅游、生产生活以及人员财产造成巨大威胁和损害。文章基于野外柱状危岩体的成生及运动边界条件,开展了颗粒柱体崩塌产生涌浪的物理试验和数值模拟。结果表明:该数值模型能较好地模拟崩塌涌浪的形成过程、矢量信息以及与水体的相互作用;速度曲线定量地展示了能量的传递;物理试验和数值模拟涌浪高度偏差约3~4 cm;数值模拟堆积区堆积角比物理试验大5%;比前缘运动距离小7%。为柱状危岩体崩塌产生涌浪灾害的预测和预警提供了重要依据。      

不同降雨条件下黄土高原浅层滑坡危险性预测评价

黄土地区浅层滑坡发育非常广泛,由于其具有分布规律性差、前期变形迹象小、分布范围大、面小点多等特征,目前还无法进行有效预测,因此给黄土地区工程安全带来严重威胁。根据无限边坡模型,结合降雨入渗-土体强度衰减规律和GIS（地理信息系统）技术,构建了不同降雨条件下黄土地区浅层滑坡发育危险性评价模型,并将该评价模型应用到延河一级支流幸福川流域,预测在有效降雨量30、50、100、200 mm条件下,该流域浅层滑坡发育程度,并与当前较为流行的SINMAP模型(地形稳定性模型)进行对比。结果表明：①不稳定和潜在不稳定浅层滑坡主要分布在末级河流的两侧和源头,稳定和较稳定区域主要分布在一级河流河道两侧和塬面上;通过对比分析,SINMAP模型计算的结果与本文建立的模型在降雨强度30 mm时的计算结果较为一致。②在本文建立的模型评价结果中,随着有效降雨量的增加,F_s（稳定性系数）<1.00的不稳定区域所占比例逐渐增加,从30 mm的1.12%到200 mm的4.79%;相反,稳定区域则出现逐渐减少的趋势。③根据已发生灾害点的分布,随着有效降雨量的增加,研究区域已发生的灾害点分布在F_s<1.25的比例明显增加,从30 mm的62%到200 mm的88%,在SINMAP评价模型中,研究区域已发生的灾害点的64%分布在不稳定和潜在不稳定区域内,说明本文所建立的评价模型具有一定的精度。通过与SINMAP评价模型对比,本文建立的模型主要采用基于降雨入渗规律,而SINMAP评价模型主要基于降雨汇流过程,因此在利用过程中应根据区域特征选择利用。     

寒区露天煤矿排土场边坡生态修复研究

通过对寒旱区生态修复技术的集成创新,结合寒区露天煤矿排土场植物生长条件特点,提出了适合矿区边坡的生态修复技术. 选择典型煤矿排土场展开现场试验,观测人工种植植物的生长情况,并采用计算流体力学数值分析手段,对排土场边坡生态修复防止风力侵蚀和降雨冲刷的效果进行了分析. 结果表明：采用边坡穴植植物装置实施的排土场生态修复工程效果良好,施工1 a后其边坡植被覆盖度达到95%,且边坡植物群落较为稳定,有效地消除了该地区冬季的风力侵蚀和夏季的降雨冲刷,彻底解决了排土场的水土流失问题.     

Impact of Doppler weather radar data on thunderstorm simulation during STORM pilot phase—2009

This study assesses the impact of Doppler weather radar (DWR) data (reflectivity and radial wind) assimilation on the simulation of severe thunderstorms (STS) events over the Indian monsoon region. Two different events that occurred during the Severe Thunderstorms Observations and Regional Modeling (STORM) pilot phase in 2009 were simulated. Numerical experiments—3DV (assimilation of DWR observations) and CNTL (without data assimilation)—were conducted using the three-dimensional variational data assimilation technique with the Advanced Research Weather Research and Forecasting model (WRF-ARW). The results show that consistent with prior studies the 3DV experiment, initialized by assimilation of DWR observations, performed better than the CNTL experiment over the Indian region. The enhanced performance was a result of improved representation and simulation of wind and moisture fields in the boundary layer at the initial time in the model. Assimilating DWR data caused higher moisture incursion and increased instability, which led to stronger convective activity in the simulations. Overall, the dynamic and thermodynamic features of the two thunderstorms were consistently better simulated after ingesting DWR data, as compared to the CNTL simulation. In the 3DV experiment, higher instability was observed in the analyses of thermodynamic indices and equivalent potential temperature (θ _e) fields. Maximum convergence during the mature stage was also noted, consistent with maximum vertical velocities in the assimilation experiment (3DV). In addition, simulated hydrometeor (water vapor mixing ratio, cloud water mixing ratio, and rain water mixing ratio) structures improved with the 3DV experiment, compared to that of CNTL. From the higher equitable threat scores, it is evident that the assimilation of DWR data enhanced the skill in rainfall prediction associated with the STS over the Indian monsoon region. These results add to the body of evidence now which provide consistent and notable improvements in the mesoscale model results over the Indian monsoon region after assimilating DWR fields.     

青藏高原隆升与欧亚内陆及北非的干旱化

通过利用一个较为完善的大气环流模式(GCM)进行了一系列青藏高原不断隆升的数值模拟试验结果.共进行了11个改变地形高度的数值试验,即对欧亚大陆上现代大地形所在地区(约10～60°N,50～140°E)陆地上所有格点的地形高度分别取为现代地形高度值的100%,90%,80%,70%,…,10%,外加一个无地形试验MOO,共完成了11个试验.结合与干旱化有关的地质记录,探讨了高原隆起在欧亚内陆及北非干旱演化过程中的作用.结果表明,仅仅改变高原地区地形高度的数值试验结果与气候变化地质记录在趋势上有可比性,青藏高原隆升是中亚及北非地区在地质时间尺度上干旱化加剧的重要原因,但却不是上述干旱区形成的根本原因.     

辽西黄土陡坡的冲刷破坏机制

以70°辽西黄土陡坡为例,在降雨强度为2.7 mm/min条件下对边坡坡面冲刷破坏特征进行了室内物理试验模拟。试验发现：随着降雨的持续坡面水流能量不断增加,致使侵蚀强度增强;边坡的侵蚀方式从试验初期的片蚀,到中期的细沟侵蚀,最后演化为坡顶部的切沟侵蚀和坍塌。基于试验成果,采用SEEP/W程序对降雨条件下边坡降雨入渗规律进行数值模拟,发现在降雨过程中坡顶部所产生的水头压力最大,随高度降低呈减小趋势;运用PFC2D颗粒流软件从微观角度对坡体土颗粒运动情况进行模拟,结果发现位于坡顶的颗粒最先被径流冲刷带走,且下落速度很快。经对比表明：数值模拟结果和物理模拟试验现象基本一致,可为进一步研究黄土边坡冲刷破坏规律提供参考。     

印度德干高原砖红壤与玄武岩风化红土磁学性质及其成因分析

印度中西部德干高原是由白垩纪末期65Ma以前多次喷发的玄武岩形成的高原。喷发间歇期间玄武岩遭受风化,形成了多层玄武岩风化红层。德干高原就是由这样一层层的溢流喷发玄武岩和风化红层相间而成,厚度达千米以上。在德干高原和南方各地的顶部普遍发育着砖红壤,该砖红壤在德干高原发育约25m厚,被认为是从玄武岩母质基础上原地风化形成,但是实地观察发现,砖红壤与玄武岩风化红土在结构、构造以及物质组成等方面均存在明显差别。常见的玄武岩喷发间歇发育的风化层厚2~3m,存在从上到下风化程度由强到弱,最后过渡到玄武岩母岩的明显层次与颜色的变化。但是德干高原玄武岩之上的25m厚砖红壤缺乏这种渐变特征,而且平坦的砖红壤顶部洼地中还发现了风积黄土层。对德干高原砖红壤、玄武岩以及玄武岩风化红土层分别采样,测量其全样粒度和磁化率、饱和磁化强度、饱和等温剩磁、非磁滞剩磁等常温磁学参数,挑选代表性样品进行磁滞回线和热磁分析。实验结果表明：1）砖红壤样品主要的磁性矿物是赤铁矿,有些同时还含微量磁赤铁矿,粒径相对较粗的玄武岩风化红土层的主要磁性矿物是磁铁矿和磁赤铁矿;2）玄武岩只含磁铁矿,并无磁赤铁矿或者赤铁矿。因此,不论是玄武岩风化红土,还是砖红壤,它们所含的磁赤铁矿以及赤铁矿都是在风化成土过程中形成的。砖红壤以赤铁矿为主和少量针铁矿,偶有样品含微量磁赤铁矿,说明该磁赤铁矿可能是母岩中的磁铁矿风化为赤铁矿的中间产物;3）玄武岩风化红土层与砖红壤不仅在磁性矿物特征方面存在差别,而且在全样粒度组成方面也存在明显差别,前者以>100μm为主,而后者以 < 100μm为主。此外,25m厚层状砖红壤除了缺乏由上而下风化程度由强变弱的差异与层次的特征之外,也缺乏砖红壤中残留的玄武岩碎屑,难以支持巨厚砖红壤由顶层玄武岩就地风化形成的说法。砖红壤厚层均匀特征似乎需要自下而上形成过程,即不断加入物质不断地风化成土才能够形成均匀厚层砖红壤。目前刚刚发现了徳干高原黄土堆积,其西北方向分布着印度沙漠,每年都有沙尘暴发生,向德干高原提供着物质来源。因此,砖红壤由风积物加积形成或许是要考虑的重要可能性之一。

     

Analysis of seasonal and annual rainfall trends for Ranchi district,Jharkhand, India

The aim of this study was to investigate temporal variation in seasonal and annual rainfall trend over Ranchi district of Jharkhand, India for the period (1901–2014: 113 years). Mean monthly rainfall data series were used to determine the significance and magnitude of the trend using non-parametric Mann–Kendall and Sen’s slope estimator. The analysis showed a significant decreased in rainfall during annual, winter and southwest monsoon rainfall while increased in pre-monsoon and post-monsoon rainfall over the Ranchi district. A positive trend is detected in pre-monsoon and post-monsoon rainfall data series while annual, winter and southwest monsoon rainfall showed a negative trend. The maximum decrease in rainfall was found for monsoon (? 1.348 mm year^?1) and minimum (? 0.098 mm year^?1) during winter rainfall. The trend of post-monsoon rainfall was found upward (0.068 mm year^?1). The positive and negative trends of annual and seasonal rainfall were found statistically non-significant except monsoon rainfall at 5% level of significance. Rainfall variability pattern was calculated using coefficient of variation CV, %. Post-monsoon rainfall showed the maximum value of CV (70.80%), whereas annual rainfall exhibited the minimum value of CV (17.09%), respectively. In general, high variation of CV was found which showed that the entire region is very vulnerable to droughts and floods.     

贵州兴义滑坡特征及过程预警研究

本文以新源县喀拉海依苏滑坡隐患体为研究案例,采用COMSOL Multiphysics数值模拟有限元软件,建立了基于非饱和渗流理论与Mohr-Coulomb准则的滑坡稳定性计算模型。根据数值模拟结果得到研究区滑坡体原始应力分布与初始孔隙压力的分布情况、在降雨入渗条件下的内部应力、有效塑性应变、塑性区、含水率、潜在滑移面等的分布情况,并计算得到滑坡体在降雨入渗条件下的安全系数。根据模型计算,滑坡体在不同降雨入渗工况下的安全系数随降雨量的增大而减小,滑坡体在连续降雨5天的临界阈值为218.82 mm,根据安全系数的变化可得到滑坡体临界降雨阈值。该论文提供了一种强度折减安全系数计算降雨型黄土滑坡降雨阈值的数值模拟方法,研究结果为西北地区降雨型黄土滑坡失稳破坏的临界降雨阈值研究提供了一种有效的研究手段。     

降雨条件下边坡角度对边坡稳定性影响的数值模拟研究

近年来,降雨所导致的边坡失稳越来越频繁,引起了越来越多专家的重视,因此对降雨条件下边坡角度对边坡稳定性的数值模拟研究无论在理论上还是在工程应用上都具有十分重要的意义。影响边坡稳定性的因素有很多,本文利用数值分析方法研究了降雨时间、边坡角度两个因素对边坡稳定性的影响,比较了降雨历时、边坡角度在降雨过程中对边坡稳定性安全系数的影响。模拟结果表明：相同的降雨强度,相同降雨时间、边坡角度越小,安全系数下降的越快,土中孔隙水压力变化越快。虽然其初始位移较小,但是随着降雨的持续,其位移将越来越大,边坡稳定性降低地越来越快; 坡内经历非稳定渗流、非稳定渗流与稳定渗流和稳定渗流3个过程。该研究结果有助于深入认识降雨引发滑坡的机制,可为治理此类滑坡提供科学依据。     

基于位移比模型的三峡库区云阳县域内蠕变型滑坡降雨预警

建立高效合理的区域滑坡灾害降雨预警模型对滑坡防治具有重要意义.然而以往的研究多侧重于临滑预警,对蠕变型滑坡在强降雨工况下的短暂加速变形的预警研究还有待深入.以三峡库区云阳县域内滑坡为例,首先根据滑坡地表位移监测数据的特点对统计样本进行合理筛选.再通过降雨因子与滑坡发生的相关性分析以及对滑坡在降雨条件下位移变化情况的数值模拟,确定了适用于不同时间阶段的降雨统计变量.然后将考虑了滑坡规模特征的滑坡位移比（累计位移与滑坡纵长之比）作为变形指标,分时段统计滑坡地表位移监测数据与历史降雨信息,建立了日降雨数据与月位移数据的对应关系,得到了可用于确定降雨量阈值的位移比模型,并获得了云阳县蠕变型滑坡的五级预警分区.最后分别选用研究区滑坡险情实例、长年位移监测数据及极端降雨事件对模型预警效果进行检验.结果显示基于专业监测数据的位移比模型的滑坡降雨预警结果与实际情况相符,可为蠕变型滑坡的预警预报提供依据.      

The Timing of Crustal Extension,Diking, and Eruption of the Deccan Flood Basalts

A randomly oriented dike swarm in the Western Ghats region has been postulated to be the feeder dike swarm of the ～2 km thick sequence exposed in that region of the Deccan province, and interpreted as evidence for the lack of crustal extension before this major flood basalt event. An enormous, central shield volcano has also been postulated in the same region based on flow stratigraphic studies and the randomly oriented dikes. These interpretations are subject to numerous objections and the lack of crustal extension before Deccan volcanism is not supported by presently available data. Rift zones of the province and the western Indian continental margin remain highly probable source areas for large volumes of the Deccan lavas.