The upper ocean response to a moving typhoon

The upper ocean response to the translation speed of typhoons is studied using a three-dimensional primitive equation model. Similar models studied previously have applied stability criteria rather than the diffusion term to simulate the vertical mixing process. This study retains the diffusion term and uses the level-2 turbulence closure scheme to estimate the vertical eddy viscosity. The model results indicate that in the forced period, the mixed-layer temperature decrease is greater for a slow-moving storm due to stronger upwelling caused by the longer residence time. A fast-moving storm can attain a similar cooling intensity in the wake period if its residence time allows the wind to resonate with the current. The significant downward momentum diffusion and advection in the first few inertial periods of these events leads to strong, persistent inertial pumping throughout the upper ocean in the wake period. The mixed layer is further cooled by turbulent mixing supported by vertical current shears. Meanwhile, the upper thermocline exhibits a compensating temperature increase. The vertical transfer magnitude and penetration scale are smaller in the slow-moving case, when the inertial motion decays rapidly. The model results also indicate that the dominant cooling process can be inferred from the non-dimensional storm speed. However, this value may be misleading for rapidly moving storms in which the current response is so distant from the storm that little wind work is performed on the ocean.     

典型厄尔尼诺期间台风降水δ18O变化分析: 以2018年22号台风“山竹”为例

台风因其特殊的物理结构, 带来的降雨有别于一般的暴雨事件, 其降水稳定同位素组成与一般的大气降水事件也有较大的差异。本文根据2018年第22号台风“山竹”登陆前后广州、东莞两地气象资料和每小时间隔的降水样品收集, 分析了此次台风在两地的降水稳定同位素变化特征及其影响因素。台风“山竹”影响期间, 广州降水δ¹⁸O值变化范围为-5.7‰~-19.2‰, 变化幅度达13.5‰, 其平均值为-15.5‰; 东莞降水δ¹⁸O值变化范围为-7.3‰~-20.0‰, 变化幅度达12.7‰, 平均值为-14.8‰; 两地降水δ¹⁸O值均呈现为3个阶段倒U型的变化特征。受到蒸发作用的影响, 两地台风前端和尾端的降水氧同位素值相对偏正, 其中广州为-5.7‰~-9.3‰, 东莞为-7.3‰~-8.1‰。两地台风中端的降水稳定同位素值极端偏负, δ¹⁸O值变化范围分别为-16.0‰~-19.2‰(广州)和-13.0‰~-20.0‰(东莞), 是该地区迄今为止已报道的最为偏负的降水δ¹⁸O值。分析认为, 在厄尔尼诺状态下生成的远源台风“山竹”强度增强, 其内部具有更强的对流和水汽循环过程, 导致降水δ¹⁸O值极端偏负。     

西北太平洋海岛地区地震背景噪声特征及海洋学解释

地震背景噪声特性及噪声源的分布研究逐渐成为深化背景噪声层析成像的关键问题.海岛地区由于特殊的地理位置,其背景噪声具有相对独特的特征.地脉动（约0.003~1 Hz）是地震背景噪声中能量最强的分量,其激发与特性被认为与海浪运动和固体地球之间的相互作用有关,但海岛地区地脉动特征与海洋波浪场之间的关系尚未被充分研究.本文利用西北太平洋海岛地震台站的连续记录数据、波浪浮标的实测数据以及WAVEWATCH-Ⅲ海浪模式的数值模拟结果,通过地震学和海洋学的交叉,分析海岛地区地脉动信号的时频特性及其与海洋波浪场之间的相关性,从海洋学角度对地脉动信号的特征及激发进行探讨与解释.结果表明,海岛地区地脉动信号相对于内陆地区更强,并具有明显且稳定的季节性变化特征：高频地脉动信号（0.12~0.32 Hz）在夏秋季节（5月-10月）相对较弱,而在冬春季节（11月-次年4月）相对较强,与北半球海洋活动季节性变化相一致.此外,海岛地区地脉动主要受周边海域波浪场影响,与周边海域波浪能功率密度及实测和数值模拟所得的有效波高均具有很好的互相关性.该研究结果同时表明可进一步发展利用地脉动观测数据反演海表波浪场的可能,为海洋科学研究中海表波浪场连续观测数据的获取提供地震学上的支持.     

Experimental characterization,design and modelling of the RBRL seismic‐isolation system for lightweight structures

The Rolling‐Ball Rubber‐Layer (RBRL) system was developed to enable seismic isolation of lightweight structures, such as special equipment or works of art, and is very versatile, a great range of equivalent natural frequencies and coefficients of damping being achievable through choice of the system parameters. The necessity to have a simple and effective design procedure has led to a new parametric experimentation at Tun Abdul Razak Research Centre (TARRC) on the rolling behaviour of the RBRL system and load–deflection behaviour of the recentering springs. The experimental results, together with theories for the rolling resistance of a loaded steel ball on a thin rubber layer and the lateral load–deflection behaviour of cylindrical rubber springs, are used to develop a general design method for the RBRL system, which allows the system to be tailored to the specific application. Sinusoidal test results are presented for the small‐deflection behaviour of the system, influenced by the presence of a viscoelastic depression on the rubber tracks beneath each ball, and an amplitude‐dependent time‐domain model is proposed, based on these results and on the steady‐state behaviour of the system. The model is validated through comparison with previously performed shaking‐table tests. Attention is here restricted to uniaxial behaviour. Copyright © 2016 John Wiley & Sons, Ltd.     

Shoulder uplift of the Western Ghats passive margin,India: a denudational model

The paper presents a denudational rift flank uplift model of the Western Ghats of Karnataka, India. The Cenozoic denudation of the Deccan plateau was constrained by relative dating of regional planation surface levels, in combination with preliminary apatite fission track results. The denudational history of the Western Ghats escarpment coastal foreland was constrained both by onshore fission track and offshore sediment data. Methods are briefly described. Results were used as reference data to elaborate a computer simulation model of both flexural rift flank upwarp and escarpment retreat from the K/T boundary to the present. Depending on the assumptions concerning the attributes of the thin elastic lithospheric sheet (infinite or semi-infinite), the shape and elevation of the initial Deccan topography (flat-lying, or affected by lithospheric updoming due to the Reunion mantle plume) and the position of the continental divide upon rifting, the flexural response to denudational unloading is shown to yield either a concave-up flexure of the Dharwar craton, or a convex, monoclinal downwarp of the margin. The relative merits of each model are discussed in the light of auxiliary field evidence, particularly from the neighbouring Deccan traps. However, the diverse assumptions on boundary conditions fail to entirely avoid geomorphological equifinality. © 1998 John Wiley & Sons, Ltd.     

New insights from low-temperature thermochronology into the tectonic and geomorphologic evolution of the south-eastern Brazilian highlands and passive margin

The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex landscape,including a northern inselberg area and a southern elevated plateau,separated by the Doce River valley.This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was the hot core of the Aracuai orogen,in Ediacaran to Ordovician times.Due to the break-up of Gondwana and consequently the opening of the South Atlantic during the Early Cretaceous,those rocks of the Araquai orogen became the basement of a portion of the South Atlantic passive margin and related southeastern Brazilian highlands.Our goal is to provide a new set of constraints on the thermo-tectonic history of this portion of the south-eastern Brazilian margin and related surface processes,and to provide a hypothesis on the geodynamic context since break-up.To this end,we combine the apatite fission track(AFT)and apatite(U-Th)/He(AHe)methods as input for inverse thermal history modelling.All our AFT and AHe central ages are Late Cretaceous to early Paleogene.The AFT ages vary between 62 Ma and90 Ma,with mean track lengths between 12.2μm and 13.6μm.AHe ages are found to be equivalent to AFT ages within uncertainty,albeit with the former exhibiting a lesser degree of confidence.We relate this Late Cretaceous-Paleocene basement cooling to uplift with accelerated denudation at this time.Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian structural network and differential erosion due to a complex interplay with the drainage system.We argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy combined with an expansion of the drainage network.We put forward the combined compression of the Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny,potentially augmented through the thermal weakening of the lower crust by the Trindade thermal anomaly,as a probable cause for the uplift.     

突发自然灾害事件网络舆情传播特征及影响因素研究

随着网络技术的发展,网络舆情分析在应对突发事件中发挥的作用日益显著.自然灾害发生后,准确把握舆情信息传播特征并分析其影响因素有助于应急管理部门及时采取有效的应急救援措施.本文以台风"利奇马"为例,基于"新浪舆情通"系统搜集的相关微博、微信、论坛、网站等全网舆情数据,探究台风灾害全过程舆情信息的时空分布特征,开展灾害舆情...     

基于Delft3D模型的风暴潮增减水模拟研究——以“9711”号台风为例

为了精确模拟"9711"号台风期间风暴潮增减水过程,考虑耦合作用下的非线性,利用Delft3D建立三维天文潮和风暴潮耦合模型,利用实测数据进行了验证,探究了台风经过日照港时风暴潮增减水过程。结果表明:(1)"9711"号台风引起的风暴潮增减水位呈现周期性变化,其变化周期与天文潮周期相近;(2)风暴潮期间,日照港西南侧海域增减水幅度较大,增水时,NE流向与SW流向的潮流在该区域相遇叠加,使增水幅度加重,减水时,该区域潮流由SW向NE流动,使减水幅度加重;(3)非线性引起的水位变化在风暴潮的水位变化过程中起负相关作用。     

利用GPS与环境负荷形变数据研究台风引起的垂向地表位移

台风造成的强降雨、低气压、海面高度变化均会引起地表的形变.本文利用中国大陆构造环境监测网(陆态网)7个GPS台站每日的垂向位移和环境负荷形变模型分析2018年9月10—26日台风"山竹"期间不同负荷引起的区域垂向地表形变.结果表明,台风期间大气负荷和非潮汐海洋负荷垂向形变最大分别达到5.1 mm和-9.2 mm.模型能较好地反映河流区域地表水文负荷变化造成的垂向形变,但不同模型之间存在系统偏差.由于缺少地下水等信息,模型反映负荷长期形变效应的效果不佳,且形变的量级明显小于GPS观测的结果.迅速增加的水文负荷使北海GPS站从开始下沉到最低点(-15.6 mm)5天的下沉量达到25.7 mm;珠海、广州GPS站均观测到河流汇水作用造成地表的二次下沉,且珠海站一周后才抬升到正常位置;湛江和北海GPS站能较好地反映河流水位变化,相关系数分别为-0.66和-0.50.研究结果表明,相比于形变模型,GPS能更有效地监测台风短期水文负荷形变,可为台风洪水等灾害监测与预报提供有用的信息.     

9806号台风异常移动特征的初步分析

９８０６号台风在其生命史中,共发生了７次突然左折和１次突然加速,形成了典型的倒抛物线型路径。本文初步分析了其异常移动的特征和原因,并详细比较了目前主要的业务预报方法对该台风的预报性能。为进一步揭示该类台风移动的物理机制积累经验,也为正确把握和使用各主要业务预报方法对该类台风预报结果的参考价值提供科学依据。