Analysis of the structure and propagation of a simulated squall line on 14 June 2009     

Lu Liu  Lingkun Ran  Xiaogong Sun 《大气科学进展》2015,32(8):1049-1062

A squall line on 14 June 2009 in the provinces of Jiangsu and Anhui was well simulated using the Advanced Regional Prediction System (ARPS) model. Based on high resolution spatial and temporal data, a detailed analysis of the structural features and propagation mechanisms of the squall line was conducted. The dynamic and thermodynamic structural characteristics and their causes were analyzed in detail. Unbalanced flows were found to play a key role in initiating gravity waves during the squall line's development. The spread and development of the gravity waves were sustained by convection in the wave-CISK process. The squall line's propagation and development mainly relied on the combined effect of gravity waves at the midlevel and cold outflow along the gust front. New cells were continuously forced by the cold pool outflow and were enhanced and lifted by the intense upward motion. At a particular phase, the new cells merged with the updraft of the gravity waves, leading to an intense updraft that strengthened the squall line.  相似文献   

福建沿岸一次飑线过程发生发展机理分析     

裴昌春  赵宇  程思 《气象科技》2019,47(5):841-850

利用常规观测资料、NCEP/NCAR(1°×1°)的逐6h再分析资料结合ARW-WRF中尺度数值模式模拟结果对2018年6月20日发生在福建沿岸的一次飑线过程的发生发展机理进行了分析,结果表明:①本次飑线过程属于槽前型,对流层低层存在发展的低涡切变,切变南侧有冷空气南下,低空西南急流不明显,但有持续的暖湿气流输送至福建中北部地区,飑线生成于低涡南侧的沿岸附近。②飑线发展期间系统南侧低层风速不断增大且维持高的水汽输送和不稳定能量;前期对流的触发因子包括锋面对流系统的冷出流、地形的抬升以及海风锋造成的冷堆强迫抬升;后期冷出流边界与海风锋边界碰撞合并,加强了低层辐合促进了对流的发展,是飑线形成的主要原因。③飑线成熟时期地面存在中高压和尾流低压,高压后部为强烈的辐散区,风速较大;成熟时期内部存在两支气流,前向入流为低层暖湿气流在飑线前方流入并在对流云区被抬升,后向入流为中层干冷空气在飑线后方流入,在低层形成下沉运动,是地面大风形成的重要原因之一。  相似文献   

郭屯矿井井筒涌水量预测及分析研究     

李云峰  温廷中 《安徽地质》2007,17(4):275-277,280

郭屯矿井井筒穿越多层地层,基岩段中含水层发育,地下水含量丰富.为了给矿井设计和施工提供可靠的水文地质参数,本文利用郭屯矿井井筒检查孔抽水试验数据,根据地下水动力学原理,准确地预算出各井筒涌水量.并结合精查地质报告,对井筒涌水量做出分析和评价.  相似文献   

The Kinematics, Physical Condition and Magnetic Field of the W3 Irs5 Region     

Hiroshi Imai  Anuj P. Sarma 《Astrophysics and Space Science》2005,295(1-2):71-75

We have independently investigated water masers associated with the star-forming region W3 IRS5 with the VLBA. Imai et al., found that the maser 3-D motions exhibit outflows, which likely originate from two of the hyper-compact HII regions in this source. Sarma et al., have detected the Zeeman effect in water masers toward W3 IRS5 and measured line-of-sight magnetic field strengths of between 14 and 42 mG. The directions of maser linear polarization are well aligned in the whole maser region and perpendicular to the estimated magnetic field. These polarimetric results are consistent with an hourglass model of the magnetic field in W3 IRS5. Imai et al., also have analyzed the microstructures found in the individual maser features (1AU), which exhibit the fractal fashion and express turbulence on very small scales. Together, we have demonstrated that observations of water masers enable us to comprehensively enhance our understanding of the early stages of the formation of massive stars in clusters.  相似文献   

疏浚物海洋倾倒区封闭条件探讨     

张士三 《台湾海峡》1998,17(1):110-114

海洋倾倒区封闭是海洋倾废管理的主要内容之一。目前疏浚物倾倒活动是一项比较频繁的海上倾倒活动。疏浚物海洋倾倒区的封闭,需要有一个相对统一的标准和判断方法,本文提出用外溢作为一种判断方法,且将倾倒 溢发为无外溢、少量外溢、显著外溢、严重外溢和最严重外溢五类,认为当倾倒区出现显著外溢时,应考虑限制使用;当倾倒区出现严重外溢时,考虑封闭;当出现危害性外溢时,就立即封闭。  相似文献   

Drainage in heterogeneous sand columns with different geometric structures     

M. Vasin  P. Lehmann  A. Kaestner  R. Hassanein  W. Nowak  R. Helmig  I. Neuweiler 《Advances in water resources》2008

This paper discusses multi-step drainage experiments in two heterogeneously packed sand columns (10 × 10 × 20 cm³). Different packing structures were generated using two different sand types. One purpose of the study was to test the influence of packing structures on the movement of water. The second purpose was to assess the quality of predictions for the outflow curves in both columns made with an upscaled model. The heterogeneous structures of the columns can be considered as two opposing extremes. The first column was packed with a random arrangement of two sand types that is not stochastically homogeneous and where a cluster running through the column exists for both materials. The second column was packed with a periodic pattern of coarse-sand inclusions in a fine-sand background and has a clearly defined unit cell. The depth-averaged (2D) spatial distribution of the water content in the columns was monitored during the whole multi-step outflow experiment using neutron radiography. The 3D water content was measured at the steady states by neutron tomography. The experimental results are compared with the model predictions of an upscaled model derived with the homogenization theory. The parameters for the upscaled model are calculated from the hydraulic parameters of the two sand types. These hydraulic parameters were first identified in independent measurements on samples of the two individual sand types, separately. Additionally, the hydraulic parameters of both sands were identified by fitting a numerical model to the measured outflow curves. The different column structures showed a significant effect on water retention and the effective retention function, as water was trapped in the coarse-sand inclusions of the periodic structure. We included this trapping effect in the effective retention function of the upscaled model with an apparent air entry pressure. Contrary to the retention, the different packing structures had no large effect on the dynamic behavior of the outflow. The effective conductivity of the columns is therefore not significantly influenced by the structure. The upscaled models predicted the movement of the averaged water content in the two columns well. This confirms the applicability of upscaled models even if the underlying requirements are not strictly met.  相似文献   

洪泽湖吞吐流二维数值模拟   总被引：3，自引：0，他引：3  

姜加虎  黄群 《湖泊科学》1997,9(1):9-14

吞吐流是湖泊中湖水运动的主要形式之一。它通过水体交换,进而对湖泊污染物质扩散,迁移,泥沙冲淤以及湖水浓度场的变化产生影响。根据洪泽湖的具体特点,本文构造了一个二维开边界数值模拟,对洪泽湖吞吐淮河的特征进行数值实验,研究其吞吐流过程。  相似文献   

Freshwater flow to the San Francisco Bay‐Delta estuary over nine decades (Part 2): Change attribution          下载免费PDF全文

Paul H. Hutton  John S. Rath  Sujoy B. Roy 《水文研究》2017,31(14):2516-2529

This paper explains observed trends in freshwater flow to the San Francisco Bay‐Delta estuary as reported in a companion paper (Hutton, Rath, & Roy, 2017 ). We employ a historical hydrologic record spanning nine decades and define a set of idealized flow scenarios to identify drivers of change in delta outflow and consequent salinity regime. Flow changes are measured against a baseline scenario representing 1920‐level land use and water management conditions. Additional scenarios are defined to represent the system absent state and federal water project reservoir and export operations, absent key non‐project reservoir operations, and absent historically‐observed sea level rise. These scenarios, in conjunction with the principle of superposition, are used to ascribe outflow and salinity trends to different anthropogenic and natural causes. We find that project and non‐project water management are attributed similar responsibility for decreasing outflow trends in April and May and consequent increasing spring salinity trends. In contrast, we find that increasing July and August outflow trends (and lagged decreasing salinity trends) are attributed to flow contributions from project water management; these contributions more than fully attenuate impacts associated with non‐project water management.  相似文献   

中国农村人口外流的时空演化及其驱动机制   总被引：5，自引：1，他引：4  

郭远智  周扬  刘彦随 《地理科学》2020,40(1):50-59

以农村户籍人口和常住人口及两者表征的农村人口外流率为研究对象,利用“五普”和“六普”数据探讨了中国农村人口外流的演化及其空间格局,在预选取影响因素的基础上,基于空间计量模型剖析了县域农村人口外流率的地域分异机制。结果显示：农村人口发展演化可划分为缓慢发展阶段、大量外流阶段、农业转移人口市民化发展阶段3个时期;全国县域农村人口外流率呈现出程度不断加深的态势,农业户籍人口和乡村常住人口的集中度下降明显,并呈现出明显的空间聚类和空间正相关性;平均海拔、人均GDP、城乡居民收入比、第一产业占比、城镇化率、道路密度、受教育水平、人均固定资产投资与农村人口外流率呈现出正相关关系,而人均耕地面积、农民人均纯收入、乡村从业人员占比与农村人口外流率呈现出负相关关系。  相似文献   

2000—2010年中国农村人力资源格局的重构     

许泽宁  高晓路  吴丹贤  廖柳文 《地理科学进展》2019,38(8):1259-1270

在城镇化快速发展和农村青壮年劳动力向城镇大规模转移的背景下,如何保证人口流出地的人口质量成为农村可持续发展和乡村振兴的关键。论文运用IPF等方法对2000年和2010年全国2294个县域空间单元的农村人口的教育年限进行了估算,并基于区域人力资源的定量测算,对2000—2010年之间全国农村人力资源的空间格局的相对变化态势进行了分析。研究发现：① 2000—2010年中国农村人力资源总量减少了3.0%,人力资源总量的空间格局变化不大,地域差异主要体现为东西差异和省际差异,空间集聚态势显著但均衡性增加;② 人均人力资源发生了很大变化,10 a间提升了17.4%,县域单元农村人力资源的相对减少主要发生在中部地区和东北地区,而西部地区、长三角、珠三角,以及地级市市辖区的农村人力资源则有所增加,人均人力资源下降的地区超过50%;③ 根据人力资源总量和人均人力资源的变化,县域单元存在同步增加、同步减少、质增量减、质减量增4种类型,2000—2010年间,平原县和丘陵县、粮食主产区、贫困县的人力资源变化需格外重视。平原和丘陵地区同步减少型县域单元的比例均超过40%;粮食主产区农村人力资源总量优势明显,但人均人力资源下降的比例高达64.6%;贫困县同步增加型地区的比例达到43.9%,但人力资源水平仍然与非贫困县有一定差距。这些研究结果表明,遏制平原县、丘陵县和粮食主产区人力资源质量下降,提升贫困县人力资源总体水平是当前农村人口可持续发展的当务之急。  相似文献