Subduction tectonics vs.plume tectonics——Discussion on driving forces for plate motion     

Ling CHEN  Xu WANG  Xiaofeng LIANG  Bo WAN  Lijun LIU 《中国科学:地球科学(英文版)》2020,63(3):315-328

Plate tectonics describes the horizontal motions of lithospheric plates,the Earths outer shell,and interactions among them across the Earths surface.Since the establishment of the theory of plate tectonics about half a century ago,considerable debates have remained regarding the driving forces for plate motion.The early"Bottom up"view,i.e.,the convecting mantledriven mechanism,states that mantle plumes originating from the core-mantle boundary act at the base of plates,accelerating continental breakup and driving plate motion.Toward the present,however,the"Top down"idea is more widely accepted,according to which the negative buoyancy of oceanic plates is the dominant driving force for plate motion,and the subducting slabs control surface tectonics and mantle convection.In this regard,plate tectonics is also known as subduction tectonics."Top down"tectonics has received wide supports from numerous geological and geophysical observations.On the other hand,recent studies indicate that the acceleration/deceleration of individual plates over the million-year timescale may reflect the effects of mantle plumes.It is also suggested that surface uplift and subsidence within stable cratonic areas are correlated with plumerelated magmatic activities over the hundred-million-year timescale.On the global scale,the cyclical supercontinent assembly and breakup seem to be coupled with superplume activities during the past two billion years.These correlations over various spatial and temporal scales indicate the close relationship and intensive interactions between plate tectonics and plume tectonics throughout the history of the Earth and the considerable influence of plumes on plate motion.Indeed,we can acquire a comprehensive understanding of the driving forces for plate motion and operation mechanism of the Earth's dynamic system only through joint analyses and integrated studies on plate tectonics and plume tectonics.  相似文献   

雷暴激发的环状重力波在中高层大气中的传播特征          下载免费PDF全文

温颖  张其林  徐寄遥  李钦增  郜海阳 《地球物理学报》2019,62(4):1218-1229

本文使用中国科学院国家空间科学中心——子午工程朔州观测站的全天空气辉成像数据,以及FY-2气象卫星云顶亮温数据（Black Body Temperature,TBB）,气象再分析数据和地闪数据,研究了2013年8月10日（LT）发生在内蒙古地区的雷暴活动激发的中高层环状重力波（Concentric Gravity Waves,CGWs）事件.根据最小二乘法的拟合结果和色散关系理论曲线,确定了激发中高层环状重力波的强对流系统,该对流中心位于内蒙古自治区中部（108.9°E,40.47°N）,重力波激发于雷暴初期,此时TBB低于220 K的深对流面积较小,随着时间的推移,该次雷暴活动越来越强,深对流面积在23：00达到最大,在23：30-24：00 LT时闪电频数最高,达到120.7 fl/min,随后深对流逐渐消散.在中高层87 km处OH（羟基）气辉层观测到的一次CGWs事件的两组波纹,分别沿水平方向传播了149.64 km和174.25 km,相应位置处的水平波长分别为12.67 km和16.75 km,周期分别为8.56 min和10.72 min,激发时间分别为19：34 LT和19：40 LT;随着水平传播距离的增加,CGWs水平波长增大.  相似文献   

游客负面口碑对大连滨海旅游形象塑造的影响研究——基于游客网络点评的文本分析          下载免费PDF全文

武传表  张珊珊 《海洋开发与管理》2018,35(7):101-106

游客口碑影响游客的消费选择和消费倾向,同时也对旅游目的地的形象塑造产生重要影响。目前我国旅游已进入全域旅游发展阶段,旅游目的地将掀起新一轮的建设,在此背景下,基于游客负面口碑研究其对旅游目的地形象塑造的影响就显得极为重要。文章通过网络文本收集游客对大连滨海旅游形象的评价和感受,从游客的视角出发,将游客负面点评网络文本数据作为研究对象,运用文本分析方法和扎根理论研究游客对大连滨海旅游形象的感知。研究发现,游客负面点评主要有5个主类目、13个次类目的消极感知因素,基于此分析了其对大连滨海旅游形象塑造的影响。为提升大连滨海旅游形象,提出了实施情感体验营销策略、完善旅游基础服务设施、健全旅游安全保障机制、提供高品质的旅游服务、营造舒适的旅游环境氛围的对策,为大连乃至同类城市旅游形象重塑提供重要依据,也丰富了以网络文本为数据来源的旅游目的地形象研究。  相似文献   

基于TRMM卫星的江西省闪电时空分布特征          下载免费PDF全文

杨钢  赖晨  支树林 《气象与减灾研究》2021,44(1):42-50

TRMM卫星闪电资料的优势在于从高空探测闪电活动,能在一定程度上反映对流云中上层的对流影响过程.利用2004—2014年TRMM卫星LIS闪电数据和江西省雷电监测定位网闪电数据对江西省境内闪电活动的时空分布特征进行了分析,并比较了两种数据之间的差异.江西省闪电活动年差异较大,季节变化明显,闪电发生高峰值为低峰值两倍多,高发期为6—9月,在该时段闪电活动多集中于午后到前半夜发生.闪电活动局地性很强,多发于江西省山地与地势较低的过渡带,正地闪高发区集中在江西省中部的偏东地区.对流有效位能(CAPE)高值区与闪电密度大值区对应,表明前者对闪电活跃区有较好的指示作用.江西省闪电时空分布与地形地势、大气环流、水热条件等诸多因素有关,卫星和地面数据之间也存在一些差异.  相似文献   

Analytical layer-element solution to axisymmetric consolidation of multilayered soils     

Zhi Yong Ai  Yi Chong ChengWen Ze Zeng 《Computers and Geotechnics》2011

After the application of a Laplace–Hankel transform, the governing equations of Biot’s consolidation are solved analytically by using the eigenvalue approach. Then the analytical layer-element of a single soil layer can be obtained in the transformed domain by synthesizing the generalized displacements and stresses, which are both expressed by six arbitrary constants. The elements of the analytical layer-element only contain negative exponential functions, which leads to a considerable improvement in computation efficiency and stability. The global stiffness matrix equation of multilayered soils is further obtained by assembling the interrelated layer-elements, and the actual solution is achieved by numerical inversion of the Laplace–Hankel transform after the solution in the transformed domain is obtained. Numerical examples are given to demonstrate the accuracy of this method and to study the influence of the layered soil properties and time history on the consolidation behavior.  相似文献   

Evolution of the Total Lightning Activity in a Leading-Line and Trailing Stratiform Mesoscale Convective System over Beijing   总被引：4，自引：0，他引：4  

LIU Dongxi  QIE Xiushu  XIONG Yajun  FENG Guili 《大气科学进展》2011,28(4):866-878

Data from the Beijing SAFIR 3000 lightning detection system and Doppler radar provided some insights into the three-dimensional lightning structure and evolution of a leading-line and trailing-stratiform (LLTS) mesoscale convective system (MCS) over Beijing on 31 July 2007. Most of the lightning in the LLTS-MCS was intracloud (IC) lightning, while the mean ratio of positive cloud-to-ground (+CG) lightning to -CG lightning was 1:4, which was higher than the average value from previous studies. The majority of CG lightning occurred in the convective region of the radar echo, particularly at the leading edge of the front. Little IC lightning and little +CG lightning occurred in the stratiform region. The distribution of the CG lightning indicated that the storm had a tilted dipole structure given the wind shear or the tripole charge structure. During the storm’s development, most of the IC lightning occurred at an altitude of ～9.5 km; the lightning rate reached its maximum at 10.5 km, the altitude of IC lightning in the mature stage of the storm. When the thunderstorm began to dissipate, the altitude of the IC lightning decreased gradually. The spatial distribution of lightning was well correlated with the rainfall on the ground, although the peak value of rainfall appeared 75 min later than the peak lightning rate.  相似文献   

The policy discourse on negative emissions,land-based technologies,and the Global South     

《Global Environmental Change》2022

Negative emissions are increasingly seen as a policy option to limit climate change. However, the most readily available technologies that could deliver negative emissions require, if deployed at scale, large amounts of land, with huge risks for livelihoods and the environment. This land is often assumed to be in the Global South. This article analyzes the nascent policy discourse on negative emissions by assessing 116 policy documents by 97 organizations with a focus on land-based technologies (afforestation and reforestation, bioenergy with carbon capture and storage, biochar, soil carbon sequestration). We conclude that this policy discourse is largely centered in the Global North (mostly in the United States, the United Kingdom, and Germany), with only five organizations directly linked to the Global South. 61% of the organizations in our sample, however, somehow refer to the Global South in their contributions, with nongovernmental organizations being most strongly focused on the role of the Global South and in particular the risks for vulnerable countries. While the earlier policy discourse on negative emissions was linked to a more general “geoengineering” discourse, this link has loosened in the last years. Overall, in the documents that we studied, negative emissions technologies seem to become more accepted, and parts of the discourse shift towards deployment. Bioenergy with carbon capture and storage seems more often associated with risks if compared to other land-based negative emissions technologies, especially with a view to the Global South.  相似文献   

蒸馏法富集纯化Os实验条件研究及其在负离子热电离质谱测量中的应用   总被引：1，自引：1，他引：0  

李欣尉  杨显德  李超  周利敏  赵鸿 《岩矿测试》2018,37(4):439-447

微蒸馏是富集纯化Os的一项重要化学前处理技术,提高Os回收率对提高Os的负离子热电离质谱(NTIMS)测量精度尤为重要。在微蒸馏过程中,蒸馏温度、吸收液体积、蒸馏时间等对Os回收率具有重要影响,但目前微蒸馏的实验条件不够明确,导致Os回收率不稳定,影响NTIMS测量精度,易增加所得Re-Os年龄误差。本文以自制的含Os溶液为对象,以ICP-MS为测量手段,对微蒸馏过程中多种实验条件对Os回收率的影响进行深入研究,以期获得最佳微蒸馏实验条件,满足后续NTIMS对Os信号强度的测量要求。结果表明:在溶液蒸干温度为120℃并保持15 min,微蒸馏温度为80℃,氢溴酸吸收液体积为15μL,微蒸馏时间为2 h的条件下,获得Os回收率为80%~90%,能够满足多种地质样品尤其是中酸性岩浆岩、热液硫化物等pg级地质样品的NTIMS测量要求,在保证Os信号强度的情况下提高了分析效率。  相似文献   

地球γ射线闪(TGFs)及其物理机制研究进展     

郄秀书  王俊芳 《地球科学进展》2010,25(9):893-906

根据卫星、地面、飞机和气球的探测结果,TGFs和与雷暴、闪电过程有关的高能辐射现象可以大致分为2类:持续时间为毫秒量级的短时间高能辐射,一般认为多数可能与闪电有关;持续时间为几秒甚至更长的长时间高能辐射,一般认为可能与雷暴有关.对已有的TGFs和与雷暴、闪电有关的高能辐射现象的观测事实、理论探索和数值模拟方面的进展进行简要的回顾,并提出目前尚未解决的问题.  相似文献   

辽宁省一次强对流天气的地闪特征     

蒋大凯  才奎志  曲荣强 《气象》2010,36(6):73-78

利用闪电定位系统、多普勒雷达和加密自动站资料对辽宁一次冷涡天气中暴雨、冰雹过程的地闪变化特征进行分析。结果表明,暴雨和冰雹过程均出现了地闪密集区,冰雹过程中正地闪占总地闪比例高于暴雨过程;暴雨过程以负地闪为主,主要分布在45 dBz以上的强回波区内,和暴雨持续时间相当,负地闪最密集区位于风暴的核心部位。负地闪频数比强回波面积提前30至70分钟到达峰值,对于短时暴雨预报预警具有一定意义。冰雹过程中,负地闪集中在雹云前部,正地闪位于雹云核心部位,与降雹区一致,正、负地闪发生区域分离。正地闪提前降雹30分钟左右发生,总地闪、正地闪频数在降雹前明显增加;降雹出现在总地闪、正地闪频数和强回波面积达到峰值及从峰值迅速下降时间段内;雹云减弱消散阶段总地闪次数减少但正闪增加。  相似文献