广东省开汛期一次连续强对流过程动力热力条件分析

2014年3月底广东省开汛期间,出现了大范围的多灾种连续强对流天气。利用区域加密地面自动站资料、风廓线雷达资料、常规观测和NCEP再分析资料,分析了此次连续强对流发生期间大尺度环流背景条件和动力热力条件,重点讨论了大气层结不稳定维持的原因。动力分析发现,强对流天气出现在低空急流的中尺度大风速中心前方强烈的辐合区和上升气流中,垂直风切变在强对流天气发生前迅速增大,具有一定的预报指示意义。中尺度低压和地面辐合线在对流落区预报中具有较好的指示性;热力分析和热流量方程诊断表明,低空西南急流由北部湾附近暖区沿温度梯度方向不断向广东输送强暖平流,使得不稳定能量得到补充,是导致广东大气层结不稳定维持的根本原因;对于广东开汛期间的强对流天气,业务预报中需要特别关注低空急流的演变及其与温度场的配置。     

Controls on the Northward Movement of the ITCZ over the South China Sea in Autumn: A Heavy Rain Case Study

The autumn Intertropical Convergence Zone(ITCZ) over the South China Sea(SCS) is typically held south of 10°N by prevailing northeasterly and weakening southwesterly winds. However, the ITCZ can move north, resulting in heavy rainfall in the northern SCS(NSCS). We investigate the mechanisms that drove the northward movement of the ITCZ and led to heavy non-tropical-cyclone rainfall over the NSCS in autumn of 2010. The results show that the rapid northward movement of the ITCZ on 1 and 2 October was caused by the joint influence of the equatorial easterlies(EE), southwesterly winds, and the easterly jet(EJ) in the NSCS. A high pressure center on the east side of Australia, strengthened by the quasibiweekly oscillation and strong Walker circulation, was responsible for the EE to intensify and reach the SCS. The EE finally turned southeast and together with enhanced southwesterly winds associated with an anticyclone, pushed the ITCZ north. Meanwhile, the continental high moved east, which reduced the area of the EJ in the NSCS and made room for the ITCZ. Further regression analysis showed that the reduced area of the EJ and increased strength of the EE contributed significantly to the northward movement of the ITCZ. The enhancement of the EE preceded the northward movement of the ITCZ by six hours and pushed the ITCZ continually north. As the ITCZ approached 12°N, it not only transported warm moist air but also strengthened the dynamic field by transporting the positive vorticity horizontally and vertically which further contributed to the heavy rainfall.     

微型钢管-旋喷复合桩在软土区的试验研究

软土地质条件下的既有建筑物地基基础加固或改造面临诸多复杂条件,施工安全和周边环境保护尤为重要,为此提出微型钢管--旋喷复合桩工艺。通过开展微型钢管--旋喷复合桩各项承载力现场试验研究,获取钢管桩应变数据,分析其承载特性及传力机制,总结提出微型钢管--旋喷复合桩承载力设计计算公式,为开展工程应用提供理论依据。     

公路路基下溶洞的探测与加固处理实践

为了弄清318国道野三关某段公路路基下溶洞的分布情况,采用地质雷达圈定了溶洞的分布范围。经过对溶洞扰动区的稳定性分析,选择注浆法对其加固处理,在溶洞加固之后进行了复测,效果显著。     

2011年7月24—25日呼伦贝尔市强降雨天气过程分析

利用常规气象资料、多普勒雷达资料和红外云图资料,对2011年7月24—25日呼伦贝尔市一次强降雨天气过程进行成因分析。结果表明：当鄂霍次克海阻塞高压强盛西伸并稳定少动,形成强大的阻挡系统时,使得西来低槽在我市西部停滞少动为强降水发生提供了有利的环流背景。中低层深厚的湿层以及西南低空急流为强降水提供充沛的水汽及能量条件。地面冷锋位置适宜且稳定少动为强降水提供了冷暖空气的触发条件。本地强对流天气潜势指数都充分表明层结的不稳定。卫星云图及雷达产品均有一定的指示意义。     

广西一次持续性强降雨过程成因分析

利用常规气象资料和NCEP再分析资料,从前期天气背景、大气环流演变及产生持续性强降雨的动力、热力和水汽等条件,分析了2008年6月广西出现的一次持续性强降雨过程。结果发现：这次持续性强降雨过程期间,500hPa环流形势稳定,高空西风小槽呈阶梯状持续下滑影响广西,不断诱发暴雨出现;200hPa广西处于南亚高压东部脊区和高空西风急流出口区右方,风速辐散明显,在高低空急流耦合作用下,华南出现了正反两支垂直环流,广西上空辐合上升运动明显,为强降雨的出现提供了极好的动力条件;南海季风暴发和副热带高压在华南沿海的稳定维持,使得华南低空形成了印度洋和南海两吏水汽通道,为暴雨区上空提供了源源不断的水汽;高温、高湿、高能的热力条件,有利于扰动的形成和对流不稳定能量产生,为广西持续性暴雨提供了必要的能量条件。     

Low-Level Jets over Southeast China: The Warm Season Climatology of the Summer of 2003

The southwesterly low-level jet (LLJ) over southeast China in the summer of 2003 is analyzed in this study. The analysis is based on the National Centers for Environmental Prediction (NCEP) Final (FNL) operational global analysis data on 1.0×1.0-degree grids at 6-h intervals. The major criteria for choosing the LLJ included the following: a maximum wind speed equal to or greater than 12.0 m s -1 , a wind direction of between 180° and 270°, and the height of wind maximum at 900-700 hPa, not confined to single pressure level. The results show that the LLJs over southeast China dominate at 850 and 800 hPa. These LLJs are closely associated with the topography of this area and tend to locate regions with large terrain gradients, including the northeastern and eastern Yunnan-Guizhou Plateau. Under the influence of mid-latitude westerly winds, the LLJs above 750 hPa move northward to the Yangtze-Huai River Basin. Compared to the ten-year (2000-2009) mean climate conditions, the LLJs in the warm season of summer 2003 were exceptionally active and strong, as reflected by the positive anomalies of LLJ occurrence numbers and wind speed. In addition, the 2003 LLJs showed strong diurnal variation, especially at pressure levels below 800 hPa. The majority of the LLJs appeared between midnight and the early morning hours (before 8 a.m.). Finally, the summary of LLJ grid numbers indicates that more than 80% of LLJs in June and July 2003 occurred within the 33-d rainy period. Thus, these LLJs are directly related to the anomalously heavy rainfall in the Yangtze-Huai River Basin.     

The East Asian Upper-Tropospheric Jet Streams and Associated Transient Eddy Activities Simulated by a Climate System Model BCC_CSM1.1

In this paper, major features of the upper-tropospheric jet streams simulated by a coupled Climate System Model BCC_CSM1.1 are evaluated through comparison with the NCEP/NCAR reanalysis. The jet streams consist of the East Asian subtropical jet (EASJ) and the East Asian polar-front jet (EAPJ). Associated stationary wave and synoptic-scale transient eddy activities (STEA) are also examined. The results show that the climatological positions of the westerly jet streams are well captured by BCC_CSM1.1, but with slight intensity biases. Statistics from the 6-h model outputs reveal that the jet core number (JCN) of ESPJ is significantly underestimated. Examination of the simulated seasonal evolution of the westerly jet stream indicates that the model has produced a westward movement of the EASJ core in May, one month earlier than that in the reanalysis. Analysis of stationary wave activities shows that the overestimated meridional wind component may have caused considerable enhancement of meridional momentum and heat transport. The stationary Rossby wave represented by the wave activity flux at the southern flank of the Tibetan Plateau is favorable to the growth of asymmetric zonal wind and the multiple-center pattern of JCN. Unlike the stationary wave heat flux transport, the model tends to systematically generate weaker transient heat flux over East Asia. Further analysis of STEA exhibits a general consistent pattern between the simulation and the reanalysis, while the intensity of the northern STEA branch associated with the EAPJ is greatly reduced. The deficiencies of eddy momentum and heat flux transport and accompanied eddy forcing may contribute to the biases of the simulated upper-tropospheric jet streams, suggesting the potential importance of midlatitude internal atmospheric dynamics in shaping the tropospheric general circulation, which is not yet fully and accurately resolved in the current BCC_CSM1.1.     

2007年7月新疆三次暴雨过程的水汽特征分析

利用新疆99个气象站日降水量资料和NECP/NCAR一天4次1°×1°再分析资料,分析了2007年7月8-11日、15-17日和27-29日新疆3次暴雨过程的水汽输送和收支特征。雨型I(8-11日)的雨带位于天山山区及其北麓,雨型II(15-17日)的雨带位于新疆东部地区,雨型III(27-29日)的雨带位于天山以北的北疆地区。结果表明,这3种典型雨型的水汽输送路径有明显的差异,雨型I存在西风气流、河西走廊至新疆的低空偏东急流和青藏高原向北气流3支水汽输送路径,西方路径水汽输送量最大,这3支水汽输送气流在天山山区及其北麓强辐合并引发暴雨。这是由700hPa贝加尔湖脊发展、对流层中亚低涡强烈发展、快速东移和500hPa新疆脊逐渐东移所造成的。雨型II的水汽输送为西方、东方、南方和北方路径,4支水汽在东—西向和南—北向强辐合并引发暴雨。这种异常的水汽输送是由700hPa柴达木低压发展、500hPa乌拉尔脊东北向发展、中亚低涡东南移动和新疆脊配置所致。雨型III主要为西风气流和贝加尔湖至新疆低空偏东急流输送水汽,东、西方水汽在天山以北区域发生强辐合并造成暴雨,偏东水汽输送来自于贝加尔湖、孟加拉湾、南海和热带西太平洋,其水汽输送量大于西方路径。这种异常水汽输送是由中亚低涡东移、西太平洋副热带高压北伸与贝加尔湖脊叠加且贝加尔湖脊西伸配置所造成的。     

A Combined Dry Jet Mixing-Prefabricated Vertical Drain Method for Soft Ground Improvement: A Case Study

A remarkable combined dry jet mixing (DJM) and prefabricated vertical drains (PVDs) method was used to enhance the performance for soft ground improvement. In the combined method, PVDs are first installed and then DJM columns are installed between the PVDs at larger spacing. This combined method improves the effectiveness of the ground improvement and creates a more economical solution. This paper presents a case study of the combined method for marine clay improvement in Lianyugang of China. The excess pore water pressure in soils created by the installation of DJM columns with and without PVDs was monitored and compared. In situ standard penetration tests were conducted in the DJM columns and before-and-after piezocone penetration tests were performed in soils surrounding the columns. Long-term settlement monitoring under embankment loading was carried out for the ground improved by combined method and DJM method alone. The field tests, settlement monitoring and economic benefit analysis results demonstrated that the DJM-PVD method is technologically sound and cost-effective as compared with the conventional DJM method.