典型旱涝年环流的旬平均和旬距平特征     

葛朝霞  钱永甫 《南京气象学院学报》1996,19(3):358-363

利用ＥＣＭＷＦ高度场资料，详细分析了１９８５年和１９９１年５月主要季风环流系统的旬平均和旬距平特征。结果表明，５月名旬，旱涝年的主要季风系统的位置和强度有明显差异。并指出夏季降水的异常，不仅与５月各旬北半球的南亚高压，极涡，西太平洋副高等系统的活动异常有关，而且与南半球的澳大利亚冷高，马斯克林高压的强弱有关，甚至与南半球中高纬环流的经向度大小也有联系。  相似文献   

云南及其邻近地区地震活动的模式识别     

钱兆霞  李晏平  龙晓帆 《地震研究》1988,(1)

本文用模式识别方法(CORA—3修改方法)研究了云南及其邻近地区大地震的发生时间与中强地震活动特性的关系。结果表明(不分子集):M≥7.0级大震前1—2年内,5—5.9级地震频度有明显增强。前1年6—6.9级地震相对减弱,前2—4年内6—6.9级地震可增至一定水平。对于CORA—3修改算法在采用“CLUSTERS”算法和不用“CLUSTERS”算法所得识别分类结果基本一致。FH(future history test)试验表明,用1930—1986年为学习时段,1969—1986年为预测时段。得到D类识别率为0.6,N类误识率为0.38。  相似文献   

陕西省冬小麦干旱风险分析及区划   总被引：14，自引：3，他引：14       下载免费PDF全文

朱琳  叶殿秀等 《应用气象学报》2002,13(2):201-206

根据自然灾害分析原理, 以县为单元, 从干旱对冬小麦造成的减产出发, 分别就各县灾损率、易灾性、抗灾能力三方面进行了讨论。以风险指数为区划指标, 在GIS系统 (City Star) 中, 按等级划分标准对各县属性值进行分级、赋色, 获得GIS系统支持下的陕西省冬小麦干旱风险区划图, 并分区予以评述。  相似文献   

干旱区内陆河流域的生态安全与生态需水量研究   总被引：2，自引：0，他引：2  

陈亚宁  郝兴明  李卫红  陈亚鹏  叶朝霞  赵锐锋 《地球科学进展》2008,23(7):732-739

结合对干旱区生态安全和生态需水量关键科学问题的探讨,提出干旱内陆河流域生态脆弱区的生态安全分析是以水过程研究为核心的,水文过程控制着生态过程,对流域生态系统的稳定性有着直接影响,而水资源开发利用和水循环对生态系统功能有重要影响,天然植物恢复和生长的合理地下水位的研究是确立生态需水量的基础。并实证分析和计算了维系塔里木河生态安全的生态需水量,塔里木河干流现状生态需水量为31.74×10⁸ m³,其中,上、中、下游分别为9.95×10⁸m³、18.47×10⁸m³和3.32×10⁸m³。  相似文献   

Advances in cloud physics and weather modification in China   总被引：2，自引：0，他引：2  

Xueliang Guo  Danhong Fu  Xingyu Li  Zhaoxia Hu  Henchi Lei  Hui Xiao  Yanchao Hong 《大气科学进展》2015,32(2):230-249

The capabilities of cloud-resolving numerical models, observational instruments and cloud seeding have improved greatly over recent years in China. The subject of this review focuses on the main progresses made in China in the areas of cloud modeling, field observations, aerosol–cloud interactions, the effects of urbanization on cloud and precipitation, and weather modification.Well-equipped aircraft and ground-based advanced Doppler and polarized radars have been rapidly applied in cloudseeding operations. The combined use of modern techniques such as the Global Positioning System, remote sensing, and Geographical Information Systems has greatly decreased the blindness and uncertainties in weather-modification activities.Weather-modification models based on state-of-the-art cloud-resolving models are operationally run at the National Weather Modification Centre in China for guiding weather-modification programs.Despite important progress having been made, many critical issues or challenges remain to be solved, or require stronger scientific evidence and support, such as the chain of physical events involved in the effects induced by cloud seeding. Current important progresses in measurements and seeding techniques provide the opportunity and possibility to reduce these deficiencies. Long-term scientific projects aimed at reducing these key uncertainties are extremely urgent and important for weather-modification activities in China.  相似文献   

三峡库区低等级土质道路侵蚀研究          下载免费PDF全文

刘窑军  王天巍  蔡崇法  李朝霞  李珩 《水科学进展》2015,26(2):169-177

以三峡库区界垭小流域内不同交通荷载土质道路为研究对象,通过自然降雨观测研究其侵蚀规律和污染物流失特征。研究结果表明,交通荷载大的干道产流率和侵蚀率均高于交通荷载低的支道,对产流率影响显著的因子主要为降雨量,对产沙率影响显著的因子为降雨量、雨强。雨型对污染物的流失特征影响显著,前期集中型降雨下,污染物流失过程线与降雨过程线同步性较好,泥沙、总氮、铵态氮、泥沙结合态磷和溶解态磷均发生了较强的初始冲刷效应;中期集中型降雨下,污染物流失浓度峰值优先于雨强峰值,且氮和磷等初始冲刷强度低于前期集中型降雨,泥沙无初始冲刷效应。  相似文献   

吉林一次降水层状云的结构和物理过程研究   总被引：6，自引：0，他引：6  

侯团结  胡朝霞  雷恒池 《气象学报》2011,69(3):508-520

利用机载粒子测量系统的探测结果,配合雷达及地面降水资料,结合一维层状云模式,通过对吉林2004年7月1日的一例降水性层状云系的宏微观物理结构和降水机制的定量化分析,对顾震潮三层模型有了进一步的认识.观测资料表明,该降水过程为典型的层状云降水,地面降水存在不均匀性,云系结构符合顾震潮三层概念模型,其中第1层为尺度很小的冰...  相似文献   

Experimental investigation of shear strength of sands with inherent fabric anisotropy   总被引：2，自引：1，他引：1  

Zhaoxia Tong  Pengcheng Fu  Shaopeng Zhou  Yannis F. Dafalias 《Acta Geotechnica》2014,9(2):257-275

Loading direction-dependent strength of sand has been traditionally characterized in the principal stress space as a direct extension of the Mohr–Coulomb criterion. A recent study found that it is more appropriate to define anisotropic strength of sand on failure/shear planes, but this proposition has only been demonstrated with discrete element method (DEM) simulations. The present study experimentally investigates anisotropic shear strength of sands in this new framework. Three granular materials with distinct grain characteristics ranging from smooth and rounded particles to flaky and angular particles are tested with the bedding plane inclination angle ψ _b varying over the full range of 0°–180°. The main objective is to study how the peak friction angle ? _p of sand is affected by the ψ _b angle and how the ψ _b–? _p relationship evolves with the change of characteristics of constituent sand particles. We find that the general trend of ψ _b–? _p curves for real sands resembles what was predicted by DEM in a previous study, whereas rich anisotropic strength behavior is revealed by the laboratory data. The effects of normal stress and initial density, as well as shear dilation behavior at different shear directions, are also studied.  相似文献   

Aircraft Measurements of the Microphysical Properties of Stratiform Clouds with Embedded Convection     

Tuanjie HOU  Hengchi LEI  Youjiang HE  Jiefan YANG  Zhen ZHAO  Zhaoxia HU 《大气科学进展》2021,38(6):966-982

The presence of embedded convection in stratiform clouds strongly affects ice microphysical properties and precipitation formation. In situ aircraft measurements, including upward and downward spirals and horizontal penetrations, were performed within both embedded convective cells and stratiform regions of a mixedphase stratiform cloud system on 22 May 2017. Supercooled liquid water measurements, particle size distributions, and particle habits in different cloud regions were discussed with the intent of characterizing the riming process and determining how particle size distributions vary from convective to stratiform regions. Significant amounts of supercooled liquid water, with maxima up to 0.6 g m~(-3), were observed between -3℃ and-6℃ in the embedded convective cells while the peak liquid water content was generally less than 0.1 g m~(-3) in the stratiform regions.There are two distinct differences in particle size distributions between convective and stratiform regions.One difference is the significant shift toward larger particles from upper -15℃ to lower -10℃ in the convective region, with the maximum particle dimensions increasing from less than 6000 μm to over 1 cm. The particles larger than 1 cm at -10℃ are composed of dendrites and their aggregates. The other difference is the large concentrations of small particles(25–205 μm) at temperatures between -3℃ and-5℃ in the convective region, where rimed ice particles and needles coexist. Needle regions are observed from three of the five spirals, but only the cloud conditions within the convective region fit into the Hallett-Mossop criteria.  相似文献   

Ecological water demand of natural vegetation in the lower Tarim River     

YE Zhaoxia  CHEN Yaning  LI Weihong 《地理学报》2010,20(2):261-272

We have appraised the relationships between soil moisture, groundwater depth, and plant species diversity in the lower reaches of the Tarim River in western China, by analyzing field data from 25 monitoring wells across eight study sites and 25 permanent vegetation survey plots. It is noted that groundwater depth, soil moisture and plant species diversity are closely related. It has been proven that the critical phreatic water depth is five meters in the lower reaches of the Tarim River. We acquired the mean phreatic evaporation of different groundwater levels every month by averaging the two results of phreatic evaporation using the Qunk and Averyanov formulas. Based on different vegetation types and acreage with different groundwater depth, the total ecological water demand (EWD) of natural vegetation in 2005 was 2.4×108 m3 in the lower reaches of the Tarim River. Analyzing the monthly EWD, we found that the EWD in the growth season (from April to September) is 81% of the year’s total EWD. The EWD in May, June and July was 47% of the year’s total EWD, which indicates the best time for dispensing artificial water. This research aims at realizing the sustainable development of water resources and provides a scientific basis for water resource management and sound collocation of the Tarim River Basin.  相似文献