一次雹暴过程的闪电活动特征及其与雹暴结构的关系     

王晨曦  郑栋  张义军  刘黎平 《热带气象学报》2014,(6):1127-1136

利用闪电定位和双多普勒雷达资料,对华南一次产生冰雹和大风的雹暴过程的闪电活动及其与雹暴动力和微物理条件的对应关系进行分析和讨论。结果表明,此次过程中地闪活动在降雹阶段和降雹后阶段表现出明显差异:降雹阶段地闪频次增减交替,较为活跃;降雹后阶段地闪活动减弱后很快再次增强,地闪频次峰值（503个/6 min）远超过降雹阶段的峰值（268个/6 min）。在分析时段中,负地闪占主导地位,正地闪比例在降雹阶段呈上升趋势。地闪活动的强弱与60 dBZ强反射率的高度变化、70 dBZ回波的出现和消失有较好的相位对应关系。对应降雹阶段,雹暴内具有更强的上升气流和更高含量的冰相粒子。降雹阶段,强上升气流区以及降雹区内地闪活动较少,降雹结束后,原降雹区域的地闪活动明显增加。研究还发现,地闪更多地出现在弱上升、弱下沉气流以及二者交界区域附近。   相似文献   

Restoration prospects for Heitutan degraded grassland in the Sanjiangyuan   总被引：4，自引：1，他引：3  

LI Xi-lai  PERRY LW George  BRIERLEY Gary  GAO Jay  ZHANG Jing  YANG Yuan-wu 《山地科学学报》2013,10(4):687-698

In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodiversity, and increase soil erosion, potentially triggering abrupt and rapid changes in ecosystem condition. Alternate stable state theory provides a framework for understanding this type of dynamic. In the Sanjiangyuan atop the Qinghai-Tibetan plateau (QTP), grassland degradation has been accompanied by irruptions of native burrowing animals, which has accentuated the loss of ground cover. Severely degraded areas of alpine meadows are referred to as ’Heitutan’. Here, using the framework of alternate stable state theory, we describe the proximate and ultimate drivers of the formation of Heitutan on the QTP, and we assess prospects for recovery, in relation to the degree of biophysical alteration, of these alpine meadows. Effective rehabilitation measures must address the underlying causes of degradation rather than their symptoms. Heitutan degradation is not uni-causal. Rather it reflects different mechanisms operating at different spatio-temporal scales across this vast region. Underlying causes include overly aggressive exploitation of the grasslands (e.g. overgrazing), amplification of grazing and erosion damage by small mammals when outbreaks occur, and/or climate change. Given marked variability in environmental conditions and stressors, restorative efforts must vary across the region. Restoration efforts are likely toyield greatest success if moderately and severely degraded areas are targeted as the first priority in management programmes, before these areas are transformed into extreme Heitutan.  相似文献   

Forces driving changes in cultivated land and management countermeasures in the Three Gorges Reservoir Area, China   总被引：2，自引：0，他引：2  

CAO Yin-gui  BAI Zhong-ke  ZHOU Wei  WANG Jing 《山地科学学报》2013,10(1):149-162

The Three Gorges project accelerates economic development in the Three Gorges Reservoir Area.This paper aimed to investigate the distribution,changes and features of cultivated land in this area,analyze the forces driving the changes in cultivated land area,and propose the countermeasures for cultivated land management.Transition matrix was used to analyze the features of cultivated land changes,and quantitative analysis and qualitative analysis were adopted to research the driving forces according to the features of cultivated land changes.Cultivated land in the Three Gorges Reservoir Area mainly lay to the northwest of the Yangtze River,especially the upper reaches.The areas of cultivated land increased from 1996 to 1999,then decreased from 2000 to 2006,and finally increased again from 2007 to 2009.The important forces driving changes in cultivated land included government policies,employment and food security,increasing construction land,agriculture structure adjustment,land rearrangement,inundation.During cultivated land management,firstly,it is necessary to insist on the principle of cultivated land protection,standardize land exploitation and strictly restrict the transformation of cultivated land into non-farming land.Secondly,land rearrangement must be implemented,which can not only increase the area of the cultivated land,but also improve the quality of the cultivated land.Thirdly,it is feasible to intensify eco-agriculture construction to increase the quantity and quality of cultivated land.Fourthly,it is helpful to improve the traditional agriculture production methods to promote cultivated land quality.Lastly,it is important to propagandize cultivated land protection and realize the enormous pressure of cultivated land shortage,making more people obligated to protect cultivated land.  相似文献   

Dynamic performance of angle-steel concrete columns under low cyclic loading-Ⅱ： parametric study     

Zheng Wenzhong Ji Jing 《地震工程与工程振动(英文版)》2008,7(2):137-146

Tests of nine angle-steel concrete column （ASCC） specimens under low cyclic loading are described in a companion paper （Zheng and Ji, 2008）. In this paper, the skeleton curves from the numerical simulation are presented, and show good agreement with the test results. Furthermore, parametric studies are conducted to explore the influence of factors such as the axial compression ratio, shear steel plate ratio, steel ratio, prismatic concrete compression strength, yield strength of angle steel and shear span ratio, etc., on the monotonic load-displacement curves of the ASCCs. Based on a statistical analysis of the calculated results, hysteretic models for load-displacement and moment-curvature are proposed, which agree well with the test results. Finally, some suggestions concerning the conformation of ASCCs are proposed, which could be useful in engineering practice.  相似文献   

Meso-Cenozoic Deformation and Dynamic Mechanism of the Ocean-continent Transitional Zone in the East China Sea Shelf Basin     

YANG Chuansheng  YANG Changqing  YANG Yanqiu  SHANG Luning  SUN Jing 《《地质学报》英文版》2019,93(Z2):225-226

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Pattern Of Green Mines On Technology Innovation and Comprehensive Utilization: Taking Baoshan Lead-Zinc Mine of Hunan Province for Example     

XU Hongyan  LIANG Zhong  CHEN Jing  LI Yichuan 《《地质学报》英文版》2019,93(Z2):447-447

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The Redefinition on Formation Time of the Lapeiquan Group in the Hongliugou Area,North Altyn: Constrains from New Detrital Zircon LA-ICP-MS U-Pb Ages     

DONG Shunli  YAN Zhaokun  REN Jing  WANG Xinwei  ZHAO Shaoze  DENG Tao 《《地质学报》英文版》2019,93(6):1971-1973

正Objective The Early Paleozoic tectonic events such as oceanic subduction and collision-orogeny in the North Altyn have been extensively studied.The Lapeiquan Group,distributed in the Hongliugou ophiolite melange belt (Fig.1),was interpreted to form along with the Ordovician Caledonian tectonic events.Based on few evidence of macrofossils,the formation age of the Lapeiquan Group  相似文献   

Discussion on possibilities of taking ground ice in permafrost as water sources on the Qinghai-Tibet Plateau during climate warming     

JiChun Wu  Yu Sheng  QingBai Wu  Jing Li  XiuMin Zhang 《寒旱区科学》2009,1(4):0322-0328

Large amounts of ground ice are born with permafrost on the Qinghai-Tibet Plateau.Degradation of permafrost resulted from the climate warming will inevitably lead to melting of ground ice.The water released from the melting ground ice enters hydrologic cycles at various levels,and changes regional hydrologic regimes to various degrees.Due to difficulties in monitoring the perma-frost-degradation-release-water process,direct and reliable evidence is few.The accumulative effect of releasing water,however,is remarkable in the macro-scale hydrologic process.On the basis of the monitoring results of water-levels changes in some lakes on the Qinghai-Tibet Plateau,and combined with the previous results of the hydrologic changing trends at the regional scale,the authors preliminarily discussed the possibilities of the degrading permafrost on the Qinghai-Tibet Plateau as a potential water source during climate warming.  相似文献   

应用雷达拼图数据估测降水试验     

伍静  刘黎平  尤卫红  崔哲虎 《四川地震》2010,(1)

利用2008年6月5～7日广东省新一代天气雷达网(广州、梅州、韶关、阳江、深圳及汕头6部雷达)的雷达原始体扫资料及自动雨量站资料,对广东省3 km高度上的雷达网系统观测值差异进行了分析,发现广州雷达的观测值比周围雷达偏高1～3 dBz,梅州雷达比其周围雷达的观测值偏低1～2 dBz。用Z-R关系和最优插值校准法分别进行6 min和1 h估测降水,并用面雨量偏差和均方根误差对该次降水估测试验做了简单评估。结果显示:6 min定量估测降水,两种方法都会低估,面雨量越大,估测效果越好;对于1 h定量估测降水,各种估测方法都有偏高或偏低情况,但普遍偏高,其中用先累加再用最优插值校准法校准的雷达-雨量计联合估测方法效果最好;短时降水估测可以很好地反映降水过程变化,而长时间降水估测可以较准确估测降水大小。  相似文献   

Paleoearthquake Studies along the Nalinlaka Fault of the Late Pleistocene in Lhasa,Tibet     

Liu Jing  Guan Peng  Shen Xuhui  Xu Yueren  Shen Junfeng  Jing Feng  Hong Shunying 《中国地震研究》2010,24(4):467-477

As the most import fault of the Late Pleistocene in the Lhasa area,the Nalinlaka fault is a left-lateral thrust fault,striking NWW,dipping SSW with a high dip angle,and extending over 33km.According to studies on the latest strata on the Nalinlaka fault zone,this fault zone has been obviously active since the Late Pleistocene and the movement left behind some geomorphologic phenomena on the earth's surface,especially at the sites of the gully west of Cijiaolin and around Xiecun village.For example,some rivers,ridges and terraces are displaced,forming beheaded gullies and fault escarps.The horizontal displacements since the Late Pleistocene at the above two places are 54m ～ 87m,20m ～ 67m,respectively.Based on studies on the 4 trenches along the fault using the progressive constraining method,we conclude that there might have been 5 paleoearthquake events along the Nalinlaka fault since 70ka B.P.,the ages of each paleoearthquake are 68.53,54.40, 41.23,21.96,9.86ka B.P.,and the average recurrence interval is 14.67ka.Because of the limits of trenches and earthquake events exposed by each trench,no single trench completely revealed all 5 events.There may therefore be some errors in determining the upper and lower limits of some events in this article.  相似文献