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1.
本研究利用加入起电、放电参数化方案的数值模式(Weather Research and Forecasting Model(Version 3.7.1),WRF3.7.1_ELEC),通过设计五组不同非感应起电及感应起电参数化方案敏感性试验,对发生在青藏高原东北部青海大通地区的一次雷暴过程进行模拟研究,对比分析了不同非感应起电机制及感应起电机制对雷暴云电荷结构的影响.结果表明:在雷暴云发展旺盛阶段,Saunders(S91)、Riming Rate(RR)、和Saunders和Peck(SP98)三种非感应起电方案模拟的雷暴云最低层均为负电荷区,而混合方案(Brooks and SP98,BSP)模拟的雷暴云最低层为正电荷区,主电荷区自下而上为"+-+-"排列的四层电荷结构.与甚高频辐射源定位法推算的结果对比,BSP方案模拟的本次高原雷暴云电荷结构更接近实际情况;几种不同非感应起电方案模拟的主电荷区外围与主电荷区电荷结构不同,说明在雷暴发展的不同阶段雷暴云的电荷结构是不同的;几种非感应起电方案模拟的电荷结构不尽相同,主要是由于霰、冰和雪粒子在不同高度所带电荷的极性及电量的大小不同,霰粒子的电荷密度对低层的影响较大,冰粒子和雪粒子的电荷密度对中上层的影响较大;加入感应起电机制后,雷暴云电荷结构分布几乎没有变化,但能使雷暴云发展旺盛阶段低层和中层的正负电荷区电荷密度有所加强.  相似文献   
2.
The prediction of soil moisture content, θ, as a function of depth, z, and time, t, is of fundamental importance for applications in many hydrological processes. The main objective of this paper is to provide an approach to solve this problem at a local scale in soils with vegetation. The matching of soil moisture vertical profiles observed under natural conditions in grassy plots and their simulations by a conceptual model is presented. Experimental measurements were performed in a plot located in Central Italy, complete with hydrometeorological sensors specifically set up and equipped with a time domain reflectometry system providing the water content, θe(z, t). A conceptual model framework earlier proposed for two‐layered soil vertical profiles was modified and adopted for simulations. The changes concern the incorporation of evapotranspiration, the reduction of the original model for applications also to homogeneous soil vertical profiles, and a correction for the differences existing between assumed and observed initial moisture contents. In the model calibration, it was found that the effects of vegetation could be represented adequately by a fictitious soil vertical profile with a more permeable upper layer of saturated hydraulic conductivity, Ks, independent of time. Then, for the validation events, the model simulations in the stages of both infiltration and redistribution/evapotranspiration reproduced appropriately θe(z, t) with typical values of root mean square error in the range 0.0017–0.0657. Similar results were obtained by applying the modified two‐layered model for simulations of experimental data observed in three other plots located in Northern Italy and Germany. For all four vegetated sites, the two‐layer profile better matched the experimental data than the assumption of a homogeneous profile. Thus, the conceptual approach based on a two‐layered scheme for representing θ(z, t) in soils with vegetation appears to be appropriate for many hydrological applications. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
3.
围绕中国科学院战略性先导科技专项"泛第三极环境变化与绿色丝绸之路建设"之子课题"热带印度洋环流动力与季风相互作用及其影响",从热带印度洋上层海洋环流、盐度变异对印度洋典型海气耦合过程的影响、印度洋海气相互作用及其对泛第三极水汽输送的影响方面回顾了热带印度洋环流动力与季风相互作用的研究进展.针对国内外研究发展的现状,提出热带印度洋上层经向、纬向、垂向流系间三维联动机制,海盆尺度热盐再分配对局地海-气模态变异的响应和反馈机制,热带印度洋典型海气耦合模态对泛第三极地区气候变化的影响机理等关键科学问题亟待解决.开展该子课题研究的最终目标是:全面认识和理解热带印度洋上层环流体系,加深印度洋海洋环流动力与海气相互作用及其对泛第三极经向水汽输送作用的理解,提高泛第三极地区气候预测水平,提升丝绸之路海上观测航道监测保障能力,从而为"一带一路"倡议和"21世纪海上丝绸之路"建设服务.  相似文献   
4.
In the sub‐humid Western Boreal Plains of Alberta, where evapotranspiration often exceeds precipitation, trembling aspen (Populus tremuloides Michx.) uplands often depend on adjacent peatlands for water supply through hydraulic redistribution. Wildfire is common in the Boreal Plains, so the resilience of the transfer of water from peatlands to uplands through roots immediately following wildfire may have implications for aspen succession. The objective of this research was to characterize post‐fire peatland‐upland hydraulic connectivity and assess controls on aspen transpiration (as a measure of stress and productivity) among landscape topographic positions. In May 2011, a wildfire affected 90,000 ha of north central Alberta, including the Utikuma Region Study Area (URSA). Portions of an URSA glacio‐fluval outwash lake catchment were burned, which included forests and a small peatland. Within 1 year after the fire, aspen were found to be growing in both the interior and margins of this peatland. Across recovering land units, transpiration varied along a topographic gradient of upland midslope (0.42 mm hr?1) > upland hilltop (0.29 mm hr?1) > margin (0.23 mm hr?1) > peatland (0.10 mm hr?1); similar trends were observed with leaf area and stem heights. Although volumetric water content was below field capacity, P. tremuloides were sustained through roots present, likely before fire, in peatland margins through hydraulic redistribution. Evidence for this was observed through the analysis of oxygen (δ18O) and hydrogen (δ2H) isotopes where upland xylem and peat core signatures were ?10.0‰ and ?117.8‰ and ?9.2‰ and ?114.0‰, respectively. This research highlights the potential importance of hydraulic redistribution to forest sustainability and recovery, in which the continued delivery of water may result in the encroachment of aspen into peatlands. As such, we suggest that through altering ecosystem services, peatland margins following fire may be at risk to aspen colonization during succession.  相似文献   
5.
To this day, field capacity (FC) is rarely defined in the context of soil properties, and the use of non-physical simplistic models is the common way to normalize water content at FC. In this study, the problem of water drainage redistribution in a soil column with and without the presence of evaporation (EV) was extensively studied. Analytical solutions for the Richards equation were established for the case of water drainage redistribution through a deeply wetted soil water column with and without EV at FC conditions. Water retention and depth evolution curves were plotted first, using different EV values of (2 mmday, 5 mmday and 8 mmday) and second, for different drainage redistribution durations of (1 day, 4 days and 6 days) where EV was set to zero for the case with no EV or to a fixed value of 5 mmday for the case with EV. The results suggest that EV plays a significant role in soil water drainage suggesting that, in the presence of EV, the FC drying front reaches much higher depths in the soil water profile than if EV is turned off. It was also concluded that FC reaches deeper depths faster the stronger EV is acting at the surface of a soil water column. Additionally, the results suggest that the texture of the soil receiving drainage controls the amount of water available for EV and as a result, EV was found to play a stronger role the smaller the hydraulic conductivity of the soil is.  相似文献   
6.
蒋碧聪  何政  朱胜 《地震学刊》2014,(5):632-636
对重大工程结构进行强地震作用下的连续倒塌全过程分析并建立相应的设计与控制方法,已成为当前地震工程领域的发展趋势。目前,由于数值求解方面的困难,绝大多数针对极端作用下的结构连续倒塌的研究止步于数值临界状态的界定,在分析过程中不能实时地对结构构件的损伤状态进行监测并根据构件的损伤状态对分析模型进行修改。为了实现连续倒塌过程中构件的逐步失效,在OpenSees程序中,基于Beam with Hinges Element构建了端部带附属节点的Beam with Hinges Element,并根据构件失效情况对附属节点的多点约束进行控制。采用三次静力凝聚方法和Newmark-beta法,给出了对此改进建模技术可信的理论背景,方法的准确性通过一个简单框架算例得到了验证。  相似文献   
7.
气溶胶对雷暴云起电以及闪电发生率影响的数值模拟   总被引:5,自引:1,他引:4  
本文利用二维耦合气溶胶模块的雷暴云起电模式,结合一次南京雷暴个例,进行250 m分辨率雷暴云起电模拟实验,探讨了气溶胶浓度对雷暴云空间电荷分布以及闪电发生率的影响。在这个气溶胶模块中,假定一个三模态的气溶胶对数分布,考虑了气溶胶活化过程。结果显示:(1)随着气溶胶浓度增大,雷暴云电荷结构保持为三极型。(2)当气溶胶浓度从50 cm-3增加至1000 cm-3时,水成物粒子浓度上升,雷暴云电荷量和闪电发生率增加明显。(3)气溶胶浓度在1000~3000 cm-3范围时,云水竞争限制了冰晶的增长,导致雷暴云上部主正电荷堆电荷量降低。云滴和霰粒子浓度缓慢上升促进中部主负电荷堆和底部次正电荷堆电荷量继续增大。闪电发生率保持稳定。(4)当气溶胶浓度大于3000 cm-3时,水成物粒子浓度稳定,云内的电荷量以及闪电发生率保持为一定量级。  相似文献   
8.
积云模式下三维闪电分形结构的数值模拟   总被引:5,自引:0,他引:5  
为了提高积云模式对雷暴云内电过程的模拟能力,将Mansell提出的放电参数化方案在起始击穿阈值和闪电通道感应电荷的分配过程上进行改进,耦合了已有的三维强风暴动力—电耦合模式中。对STEPS(Severe Thunderstorm Electrification and Precipitation Study)试验中一次雷暴个例以及对中纬度地区理想雷暴个例的模拟表明,引入了新放电参数化方案的模式模拟出闪电在发展特性和几何结构上和观测结果有较好的一致性。模拟结果还表明:闪电的类型与极性取决于背景电荷结构以及闪电的起始位置,只有底部存在正电荷堆时才会产生负地闪,且负地闪的起始点均具有较高的负电势。闪电通道上感应电荷的沉降会改变通道附近水成物粒子上携带的电荷,这对雷暴云内复杂电荷结构的形成有重要作用。经统计,模拟的地闪和云闪通道的分形维数平均值分别为1.47和1.69。对起始击穿阈值的敏感性试验表明,随着起始击穿阈值的增大,首次闪电时间会向后推迟,当采用逃逸击穿时首次闪电产生的时间最早;闪电数量随起始击穿阈值的增大而减少;当使用固定击穿阈值(100,150和200 k V)时得到的云地闪比均小于使用逃逸击穿时得到的云地闪比,使用逃逸击穿时得到的云地闪比与观测结果最为接近。  相似文献   
9.
利用低光度相机首次观测到了2013年7月31日华北地区一次中尺度对流系统(MCS)上空产生的中高层Sprite放电现象。结合闪电定位、天气雷达等同步观测, 对一次MCS诱发的Sprite的形态学特征及其对应的母体闪电和雷暴系统的雷达回波特征等进行了详细分析。研究除发现了2例圆柱型、3例胡萝卜型和1例舞蹈型 Sprite外, 还发现了2例发光主体发育不完全的Y字型Sprite。估算的Sprite的底部平均高度低于61.8±3.5 km, 顶部平均高度为84.3±6.8 km。Sprite持续时间算术平均值为25.7±9.8 ms, 几何平均值为24.4 ms。Sprite的母体闪电均为正地闪, 峰值电流在+62.5~+106.2 kA之间, 算术平均值为+77.1±22.2 kA, 是本次MCS所有正地闪平均峰值电流的1.4倍。Sprite母体闪电的脉冲电荷矩变化(iCMC)在+475~+922 C km之间, 几何平均值为+571.0 C km。Sprite母体闪电发生在MCS雷达回波25~35 dBZ的层状云降水区, 弱回波(<30 dBZ)面积的突然增加对Sprite的产生有重要指示作用。Sprite易发生在MCS成熟—消散阶段正地闪比例(POP)显著增加的时段。在本次MCS消散阶段中, 有两个时间段可能有利于产生Sprite。在Sprite集中发生时间段, 北京闪电综合探测网(BLNET)探测到的正地闪比例为54.2%, 正地闪连续电流比例70.24%, 连续电流持续时间为58.17±50.31 ms, 有利于Sprite的产生。  相似文献   
10.
台风莫拉菲(2009)登陆前后电荷结构演变的模拟研究   总被引:3,自引:0,他引:3  
利用中尺度起电放电模式以及卫星和闪电定位等观测资料,对比分析了台风莫拉菲(2009)在登陆前后以及衰亡阶段的电荷结构及形成。结果表明:莫拉菲在登陆前存在近海加强过程,加强中逐渐形成清晰的台风眼并伴随眼壁区闪电活动的多发。眼壁区对流在近海加强阶段呈现正的三极性电荷结构,主负电荷区位于-25℃——10℃层,其上下各有一个正电荷区。而在台风达到最大强度后呈现负的偶极性电荷结构,仅存在云中部的负电荷区和下部的正电荷区。眼壁区对流的电荷结构同台风强度变化密切相关而不受登陆直接影响。在台风发展的不同阶段,外螺旋雨带对流主要表现为正的三极性或正的偶极性电荷结构,之前的研究一般认为外雨带对流只能呈现正的偶极性电结构。外雨带三极性电结构的形成可以类似于眼壁区三极性结构的形成,也存在其他形成机制,即在霰粒子与冰晶组成的正偶极性电荷结构下存在一个由雹粒子组成的正电荷区,从而形成正的三极性电荷结构。台风衰亡阶段对流主要表现负的偶极性电荷结构,对流活动较弱,类似于陆地雷暴消散阶段的特性。不同类型的电荷结构所对应对流的相对强度也在文内进行了讨论。  相似文献   
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