Mesoscale Diagnosis of a Torrential Rainfall Caused by a Tropical Depression     

YU Hui  LIANG Xudong  DUAN Yihong  QI Liangbo 《Acta Meteorologica Sinica》2005,19(2):226-230

On August 5, 2001, Shanghai was struck by a torrential rainfall due to the passage of a tropical depression (TD). The rainfall intensity has been the strongest in recent 50 years. In this paper, a set of mesoscale re-analyses data and the planetary boundary layer observation from a wind profiler are used to understand the possible mechanism of such a heavy rain. Results show that the outburst of a southerly jet in the lower atmosphere triggered the explosive development of cyclonically vertical vorticity in the region with steep potential temperature surfaces in front of the TD; while the cyclonic vorticity increased notably at higher levels due to the small atmospheric vertical stability of westerly currents in the vicinity of Shanghai. The simultaneous sharp development of cyclonic vorticity at different levels should be the main cause for the torrential rainfall.  相似文献   

Analytical solutions for advective–dispersive solute transport in double‐layered finite porous media     

Peter John Cleall 《国际地质力学数值与分析法杂志》2011,35(4):438-460

Analytical solutions for advection and dispersion of a conservative solute in a one‐dimensional double‐layered finite porous media are presented. The solutions are applicable to five scenarios that have various combinations of fixed concentration, fixed flux and zero concentration gradient conditions at the inlet and outlet boundaries that provide a wide number of options. Arbitrary initial solute concentration distributions throughout the media can be considered via explicit formulations or numerical integration. The analytical solutions presented have been verified against numerical solutions from a finite‐element‐based approach and an existing closed‐form solution for double‐layered media with an excellent correlation being found in both cases. A practical application pertaining to advective transport induced by consolidation of underlying sediment layers on contaminant movement within a capped contaminated sediment system is presented. Comparison of the calculated concentrations and fluxes with alternative approaches clearly illustrates the need to consider advection processes. Consideration of the different features of contaminant transport due to varying pore‐water velocity fields in primary consolidation and secondary consolidation stages is achieved via the use of non‐uniform initial concentration distributions within the proposed analytical solutions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Short-lived polyphase deformation during crustal thickening and exhumation of a collisional orogen (Ribeira Belt,Brazil)     

《Journal of Structural Geology》2016

The Ribeira Belt (Brazil) is a Neoproterozoic collisional-related feature that was located in a south-central position in West Gondwana. We present quantitative data on finite strain, flow vorticity and deformation temperatures for the Curitiba Terrane, a major segment of the southern Ribeira Belt. Six deformation phases (D₁-D₆) related with crustal thickening and exhumation were recognized. D₁ and D₂-related microstructures are preserved exclusively within porphyroblasts, in part grown during stages of high-pressure (∼9–12 kbar) isobaric heating after crustal thickening. D₃ phase was active from peak metamorphism attained in contrasting crustal levels (810–400 °C), to the early stage of exhumation (500–400 °C), as indicated by petrological, microstructural and quartz c-axis fabric evidence. Kinematic vorticity results indicate that the SL₃ mylonitic fabric resulted from a simple shear-dominated deformation related with westward thrusting. North-verging overturned D₄ folds with E-W-trending subhorizontal axes derived from a pure shear-dominated deformation. Regional D₅ open folds with subvertical axes and NNE-SSW-trending traces were produced by indentation tectonics. D₆ phase comprises retrograde orogen-parallel transcurrent shear zones related with scape tectonics. Geochronological data indicate that D₃-D₆ phases occurred between 584 and 580 Ma, suggesting a fast exhumation rate of ∼8 mm/year for the deepest rocks from the southern Ribeira Belt.  相似文献   

Role of horizontal density advection in seasonal deepening of the mixed layer in the subtropical Southeast Pacific     

Qinyu Liu  Yiqun Lu 《大气科学进展》2016,33(4):442-451

The mechanisms behind the seasonal deepening of the mixed layer(ML) in the subtropical Southeast Pacific were investigated using the monthly Argo data from 2004 to 2012. The region with a deep ML(more than 175 m) was found in the region of(22?–30?S, 105?–90?W), reaching its maximum depth(～200 m) near(27?–28?S, 100?W) in September. The relative importance of horizontal density advection in determining the maximum ML location is discussed qualitatively. Downward Ekman pumping is key to determining the eastern boundary of the deep ML region. In addition, zonal density advection by the subtropical countercurrent(STCC) in the subtropical Southwest Pacific determines its western boundary, by carrying lighter water to strengthen the stratification and form a "shallow tongue" of ML depth to block the westward extension of the deep ML in the STCC region. The temperature advection by the STCC is the main source for large heat loss from the subtropical Southwest Pacific. Finally, the combined effect of net surface heat flux and meridional density advection by the subtropical gyre determines the northern and southern boundaries of the deep ML region: the ocean heat loss at the surface gradually increases from 22?S to 35?S, while the meridional density advection by the subtropical gyre strengthens the stratification south of the maximum ML depth and weakens the stratification to the north. The freshwater flux contribution to deepening the ML during austral winter is limited. The results are useful for understanding the role of ocean dynamics in the ML formation in the subtropical Southeast Pacific.  相似文献   

The impact of deformation on vortex development in a baroclinic moist atmosphere     

Na Li  Lingkun Ran  Shouting Gao 《大气科学进展》2016,33(2):233-246

A mathematical relation between deformation and vertical vorticity tendency is built by introducing the frontogenesis function and the complete vertical vorticity equation, which is derived by virtue of moist potential vorticity. From the mathematical relation, it is shown that properly configured atmospheric conditions can make deformation exert a positive contribution to vortex development at rates comparable to other favorable factors. The effect of deformation on vortex development is not only related to the deformation itself, but also depends on the current thermodynamic and dynamic structures of the atmosphere, such as the convective stability, moist baroclinicity and vertical wind shear(or horizontal vorticity). A diagnostic study of a heavy-rainfall case that occurred during 20–22 July 2012 shows that deformation has the most remarkable effect on the increase in vertical vorticity during the rapid development stage of the low vortex during its whole life cycle. This feature is mainly due to the existence of an approximate neutral layer(about 700 h Pa) in the atmosphere where the convective stability tends to be zero. The neutral layer makes the effect of deformation on the vertical vorticity increase significantly during the vortex development stage, and thus drives the vertical vorticity to increase.  相似文献   

中亚低涡背景下南疆西部两次强冰雹环境场对比分析     

张云惠  谭艳梅  于碧馨  黄艳 《沙漠与绿洲气象(新疆气象)》2016,10(4):10-16

利用常规资料、14:00加密探空、NCEP1°×1°再分析资料,对比分析2013年6月18日和2014年6月23日南疆西部两次强冰雹环境场及物理机制,表明两次冰雹环境场有相同之处:在环流经向度较大的中亚低涡背景下,前期有明显降水,傍晚前后由中亚低涡后部西北气流下产生,高空干冷平流、低层暖湿环境、较大的垂直温度递减率及低层辐合线或切变线为冰雹天气提供了强不稳定层结和动力触发条件,为冷平流强迫类型。但两次冰雹中亚低涡位置、强度、物理机制变化等有所不同:"6·18"中亚低涡压至南疆西部,低涡强,西北风大,而"6·23"中亚低涡在巴尔喀什湖附近,位置偏北,低涡较弱,西北风较小;"6·18"偏西北气流、风(垂直)切变、强回波伸展高度、层结不稳定、水汽及动力等变化均较"6·23"明显偏强;"6·18"的0℃层和-20℃层的高度均比"6·23"的低300~400 m;"6·18"低层南疆盆地偏东风日变化明显,即傍晚到夜间增强,山前东西风辐合促使上升运动发展,并有明显的中尺度垂直环流圈,而"6·23"低层为西北风风速辐合及与偏东风的切变。  相似文献   

承德市2015年2月20-21日强降雪成因分析     

杨杰  谭国明  尤国军  冯钰博  刘园园 《沙漠与绿洲气象(新疆气象)》2016,10(4):32-38

利用常规观测资料、卫星云图和NECP (1?? 1?)逐6h再分析资料,对承德市2015年2月20～21日强降雪过程环流形势和物理量场进行了分析。结果表明：在此次强降雪过程中,中、低层的西风槽、切变线和地面上东移加强的蒙古气旋构成了有利天气形势,在这些系统的共同作用下不断有干冷空气侵入承德地区与低层西南暖湿气流交汇,持续的西南暖湿气流对此次强降雪的形成和维持至关重要。相对湿度、水汽通量、垂直速度、涡度及垂直螺旋度的分布和演变很好的反映出了此次强降雪过程中物理量场特点：相对湿度和水汽通量的分布说明强降雪区上空湿度较大且有充足的水汽供应,水汽通量的增大与降雪的增强相一致,水汽通量大值中心与强降雪有很好对应关系。强降雪区上空伴有较强上升运动;降雪区上空均为正涡度时最有利于上升运动和降雪;降雪区上空垂直螺旋度均为正或呈"上负下正"的垂直结构均有利于降雪,低层正垂直螺旋度对强降雪变化有很好的指示意义。  相似文献   

1999年北京持续高温天气过程的诊断分析     

吴振鹏  武媛  李乃杰 《气象与环境科学》2016,39(1):82-88

利用北京观象台观测资料和NCEP/NCAR再分析数据,对1999年6月24日至7月2日北京一次持续性高温天气的演变和发展过程及非绝热加热作用对系统的影响进行诊断分析,结果表明：在此次高温天气发生前,欧亚大陆中高纬度环流经向度很大,欧洲北部和贝加尔湖以南为高压脊控制,中亚和我国东北地区则处于低压槽内。贝加尔湖南部的高压脊纬向延伸范围较广,在东移过程中长时间影响北京。随着贝加尔湖以南的高压脊逐渐东移,北京上空下沉增温与非绝热加热作用有所增强,北京逐渐受到高温天气影响。在高温天气发生的后半阶段,我国东北的低压槽入海后在120130°E附近维持并发展,槽前非绝热加热率很大。从垂直方向来看,加热率在500 hPa以下随高度迅速增加,根据全型涡度方程,强烈的非绝热加热率垂直分布不均作为一个明显的涡度源区,对入海低压槽的稳定维持有显著的作用。而入海低压槽的稳定维持,又阻碍了华北高压脊的东移,使其在北京地区长时间稳定少动,为北京带来多日的持续性高温天气。  相似文献   

中国东部城市群发展对南海夏季风爆发影响的模拟研究     

余荣  江志红  马红云 《大气科学》2016,40(3):504-514

本文利用NCAR开发的CAM5.1(Community Atmosphere Model Version 5.1)模式,针对我国东部大规模城市下垫面发展对南海夏季风爆发的影响进行了数值模拟研究。结果表明我国东部大规模城市群发展可能使得南海夏季风提前1候爆发;机理分析表明:在南海夏季风爆发之前,中国东部城市群发展引起的陆面增温,使得南海及其附近地区南北温差提前逆转、中国东部区域海平面气压降低,导致中南半岛到南海地区西南气流加强,中南半岛到南海地区降水增加,而凝结潜热垂直变化强迫出的异常环流,促进了南亚高压的加强及提前北跳,相伴随的高层抽吸作用有助于季风对流的建立和西太平洋副高的减弱东撤,从而形成了有利于南海夏季风爆发的高低层环流条件,导致南海夏季风提前爆发。另外,观测结果表明1993年之后南海夏季风爆发的日期相对上一个年代明显提前约2候,城市化快速发展阶段与南海夏季风爆发的年代际变化存在时间段的吻合,表明城市下垫面发展可能是南海夏季风提前爆发的原因之一。  相似文献   

运动学涡度在藏南冈底斯岩浆带中段谢通门-曲水韧性剪切带中的应用     

孟元库  许志琴  马士委  刘晓佳 《地质学报》2016,90(11):3023-3038

一般剪切带主要由纯剪切和简单剪切共同作用,不同的剪切带及不同的构造位置两者所占有的比例不同。利用运动学涡度(Wk)可以定量地分析两者间的比值大小。本文通过极莫尔圆法和有限应变轴率Rs/石英c轴组构法对冈底斯岩浆带中段谢通门-曲水滑覆型韧性剪切带的运动学涡度进行了计算,两种方法获得了较为一致的结果。通过极莫尔圆法,对剪切带中的9组糜棱岩样品进行了运动学涡度计算,获得了Wk=0.73~0.96,平均值Wk=0.83。运用有限应变轴率Rs/石英c轴组构法对4个样品进行了分析,得到Wk=0.85~0.93,均值为0.88,两种方法获得了较为一致的应变结果。还根据极莫尔圆图解,计算了该韧性剪切带的减薄量S=0.09~0.35,平均减薄量为0.20。研究表明该韧性剪切带为典型的以简单剪切为主伴有部分纯剪切的一般剪切,该剪切带的形成可能与拉萨地体在中新世时从挤压到侧向伸展的转换有关。该剪切带变形特征和运动学涡度的确定深化了对藏南冈底斯地区的构造演化过程的理解,并对青藏高原中南部的地质研究具有推进作用。  相似文献