TTI介质拟声波方程数值模拟

TTI介质qP波数值模拟方法因为考虑了倾角因素,可以比VTI介质qP波数值模拟方法更加准确地描述各向异性介质中地震波场的传播规律。文中用拟声波方程对TTI介质中的地震波场进行了高阶有限差分数值模拟,在改进衰减函数分布方式后,通过坐标变换,利用改进的完全匹配层(perfectly matched layer,PML)边界控制方程对波场边界进行吸收处理,取得了良好的效果;然后分析了拟声波方程数值模拟中的稳定性问题,并对波场中的伪横波进行压制。通过对不同模型的数值模拟,验证了文中使用的TTI介质拟声波波动方程的稳定性以及所采用的PML边界控制方程的可靠性和适用性。     

四川江油马角坝刺林包剖面二叠-三叠系间粘土岩研究

二叠-三叠纪之交华南地区普遍发育火山成因的粘土岩,其对于了解二叠纪末大规模火山活动及扬子板块碎屑物质来源具有重要意义。本文对扬子西缘马角坝刺林包剖面飞仙关组底部粘土岩进行了碎屑锆石U-Pb定年及原位Hf同位素测试、X衍射和全岩地球化学分析,以揭示粘土岩的岩石成分及物源信息。镜下特征、X衍射及主量元素特征表明岩石中粘土矿物主要为伊利石,含少量方解石、石英。碎屑锆石年龄显示,特征峰值年龄主要集中在2 615~2 383、1 868~1 328、1 186~778和430~246 Ma,并出现~250 Ma特征高峰,结合原位Hf同位素特征表明锆石与秦岭造山带、华南典型PTB剖面粘土岩及峨眉山大火成岩省具有较高的相似性。同时,通过微量、稀土元素分析发现粘土岩中Zr、Hf、Th、Cr、Co、Ti相对富集,与华南典型PTB粘土岩和峨眉山玄武岩相近,并结合构造背景及锆石特征,综合认为刺林包剖面PTB粘土岩来自于秦岭造山带及龙门山岛链局部剥蚀区、二叠纪末火山活动和峨眉山大火成岩省剥蚀岩体。     

Episodic crustal growth in the Tanzania Craton: evidence from Nd isotope compositions

The analysis of available Nd isotope data from the Tanzania Craton places important constraints on the crust-mantle separation ages, and events marking juvenile crustal addition and crustal recycling. Nd model ages date the oldest crust extraction to 3.16 Ga in the Tanzania Craton, although a rock record of such antiquity is yet to be found there. The most significant period of juvenile crustal addition as well as crustal recycling is 2.7–2.6 Ga. The Nd isotopes of mafic samples show that chemical heterogeneity existed in the mantle beneath the Tanzania Craton, with some samples originating from significantly depleted mantle, and most samples originating from the mixture of primitive mantle and depleted mantle. The Nd isotope section reveals significant differences in Nd isotopes between the north craton and central craton; compared to the north craton, the central craton yields a Nd model age that is approximately 100 Ma older, and its ε_Nd(t) values are more negative, indicating that the two parts of the craton have different mantle source regions. Different types of granitoids are distributed in the Tanzania Craton, such as high-K and low-Al granite, calc-alkaline granite, peraluminous granite and transitional types of tonalite-trondhjemite-granodiorites (TTGs). Most of the granitoids formed later than the mafic rocks in syn-collision and post-collision events.     

Sedimentology of the continental end‐Permian extinction event in the Sydney Basin,eastern Australia

Upper Permian to Lower Triassic coastal plain successions of the Sydney Basin in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of palaeoenvironmental change at high southern palaeolatitudes in a continental margin context for the late Permian (Lopingian), across the end‐Permian Extinction interval, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the late Permian and, to a much lesser extent, during the Early Triassic, allowing high‐resolution age determination on the numerous tuff horizons. Palaeobotanical and radiogenic isotope data indicate that the end‐Permian Extinction occurs at the top of the uppermost coal bed, and the Permo‐Triassic boundary either within an immediately overlying mudrock succession or within a succeeding channel sandstone body, depending on locality due to lateral variation. Late Permian depositional environments were initially (during the Wuchiapingian) shallow marine and deltaic, but coastal plain fluvial environments with extensive coal‐forming mires became progressively established during the early late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. However, apart from the loss of peat‐forming mires, no significant long‐term change in depositional style (grain size, sediment‐body architecture, or sediment dispersal direction) was noted across the end‐Permian Extinction (pinpointed by turnover of the palaeoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from these successions. Rather, the end‐Permian Extinction marks the base of a long‐term, progressive trend towards better‐drained alluvial conditions into the Early Triassic. Indeed, the floral turnover was immediately followed by a flooding event in basinal depocentres, following which fluvial systems similar to those active prior to the end‐Permian Extinction were re‐established. The age of the floral extinction is constrained to 252.54 ± 0.08 to 252.10 ± 0.06 Ma by a suite of new Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry U‐Pb ages on zircon grains. Another new age indicates that the return to fluvial sedimentation similar to that before the end‐Permian Extinction occurred in the basal Triassic (prior to 251.51 ± 0.14 Ma). The character of the surface separating coal‐bearing pre‐end‐Permian Extinction from coal‐barren post‐end‐Permian Extinction strata varies across the basins. In basin‐central locations, the contact varies from disconformable, where a fluvial channel body has cut down to the level of the top coal, to conformable where the top coal is overlain by mudrocks and interbedded sandstone–siltstone facies. In basin‐marginal locations, however, the contact is a pronounced erosional disconformity with coarse‐grained alluvial facies overlying older Permian rocks. There is no evidence that the contact is everywhere a disconformity or unconformity.     

Role of the Nocturnal Low-level Jet in the Formation of the Morning Precipitation Peak over the Dabie Mountains

The diurnal variation of precipitation over the Dabie Mountains(DBM) in eastern China during the 2013 mei-yu season is investigated with forecasts of a regional convection-permitting model. Simulated precipitation is verified against surface rain-gauge observations. The observed morning precipitation peak on the windward(relative to the prevailing synoptic-scale wind) side of the DBM is reproduced with good spatial and temporal accuracy. The interaction between the DBM and a nocturnal boundary layer low-level jet(BLJ) due to the inertial oscillation mechanism is shown to be responsible for this precipitation peak. The BLJ is aligned with the lower-level southwesterly synoptic-scale flow that carries abundant moisture.The BLJ core is established at around 0200 LST upwind of the mountains. It moves towards the DBM and reaches maximum intensity at about 70 km ahead of the mountains. When the BLJ impinges upon the windward side of the DBM in the early morning, mechanical lifting of moist air leads to condensation and subsequent precipitation.     

GRAPES全球奇异向量方法改进及试验分析

基于总能量模的奇异向量扰动常用于构造集合预报的初始条件。以建立GRAPES（Global and Regional Assimilation PrEdiction System）全球集合预报系统为目的,基于前期研发的GRAPES全球模式奇异向量方法,在GRAPES全球切线性模式和伴随模式2.0版的框架下,开展了引入线性化边界层方案来改善奇异向量结构,并提高奇异向量计算效率的研究。通过连续试验,从奇异向量的扰动能量结构、扰动能量谱及扰动空间分布等方面,综合分析改进GRAPES全球奇异向量的结构及演变特征。试验结果表明,改进后的GRAPES奇异向量方法有效抑制了之前扰动能量在近地面层不合理的快速增长,同时,奇异向量最优扰动的结构更客观地体现了中高纬度区域大气初始条件中的斜压不稳定扰动及其演变,如在初始时刻奇异向量扰动能量主要位于对流层中层,并呈现出随高度向西倾斜的大气斜压特征;经过线性化演变,扰动能量向较大水平尺度转移,并在垂直结构上表现出向对流层高层上传及向对流层低层下传的特征等。针对GRAPES奇异向量迭代求解中伴随模式计算耗时为主的情况,改进伴随模式中广义共轭余差方案的调用方式,并采用大内存存储法来提高其计算效率,进而将奇异向量总计算时间缩短了25%。总之,改进后的GRAPES奇异向量方法,可应用于构建面向业务应用的GRAPES全球集合预报系统。      

辽宁绥中地区海陆风的多普勒测风激光雷达观测与特征提取

2019年3月,利用相干多普勒测风激光雷达首次在辽东湾西部绥中地区进行了风廓线测量试验。根据研究区域海岸线走向采用风向的十六分位法定义局地海风和陆风,分析和提取海陆风特征验证了多普勒测风激光雷达在春季季风间断期间观测海陆风的可行性,并计算和分析了大气边界层湍流能量的变化以及回流水平变化等特性。结果表明：1）绥中地区春季存在明显的海陆风环流特征,测风激光雷达观测海陆风出现的时间与地面自动气象站观测的数据较为一致,符合海陆风日的定义。2）海陆风日发生时,水平局地回流指数（RF）较小,1.2 km以下的RF值小于0.5,使得污染物循环累积,较易形成雾霾天气;但是海风时大气边界层的高度可达1 km以上,有利于低层大气污染物向高层扩散,减轻低层大气污染。研究结果为该地边界层参数化方案的设计和污染的防治提供了参考依据。     

GRAPES区域集合预报两种侧边界扰动方法对比试验

中国气象局数值预报中心自2014年建立了区域集合预报业务系统,其使用的侧边界扰动由全球集合预报系统动力降尺度得到。为深入了解侧边界扰动对区域集合预报的影响,基于15 km水平分辨率的区域集合预报模式,使用动力降尺度方法和尺度化滞后平均法(scaled lagged average forecasting,SLAF)设计构造了两种侧边界扰动方案,并开展了2015年7月共6天的集合预报试验,利用集合均方根误差、集合离散度、连续分级概率评分、离群值、Brier Score及相对作用特征曲线面积等概率预报检验方法进行了多方面检验,分析了两种侧边界扰动方案对区域集合预报质量的影响。结果表明:动力降尺度侧边界扰动方案(DOWN)的扰动总能量在各垂直层次均大于SLAF方案,使得边界上前者的离散度大于后者,集合扰动增长更为合理;对于等压面要素和地面要素,DOWN方案的离散度、Outlier、CRPS等评分优于SLAF方案,反映了DOWN方案构造的侧边界扰动更加合理;在降水概率预报技巧方面,SLAF方案在评分上具有一定优势,但评分的提高没有通过显著性水平检验,因此认为两种方案对降水预报的改进基本相当。     

边界层参数化对海南岛海风环流结构模拟的影响

利用WRF V3.7详细分析了应用8种边界层参数化方案（YSU、MYNN2.5、MYNN3、ACM2、BouLac、UW、SH、GBM）所模拟的2014年5月25日海南岛海风环流结构的差异,其中YSU、ACM2和SH为非局地闭合方案,MYNN2.5、MYNN3、BouLac、UW和GBM为局地闭合方案。结果表明:对于海风环流水平结构的模拟,15时,YSU、ACM2、BouLac、UW和SH模拟的北部海风较强,SH和GBM的内陆风速偏大。温度与海风发展强度相对应,MYNN2.5与MYNN3模拟的岛屿温度偏低,海陆温差小,海风相对较弱。对于海风环流垂直结构的模拟,09时海风开始,但强度较小,且存在残余陆风,向内陆传播距离较短,YSU、MYNN2.5和SH方案的海风相对较强。12时,海风已呈现出较为清晰的环流结构,YSU和ACM2的海风厚度及向内陆传播距离相对强于其它方案,MYNN3的环流结构则不太明显,且向内陆推进距离短,海风相对较弱。15时,海风发展强盛,MYNN2.5和MYNN3方案模拟的海风垂直强度较小,ACM2方案的海风垂直环流特征最为明显。18时,海风的强度和扰动均有所减弱,ACM2、BouLac和UW的整体海风相对强于其它方案。21时海风已基本转为陆风,BouLac与UW的陆风环流结构最为清晰。位温、水汽及海风垂直环流强度的发展变化与海风的演变过程基本一致。造成ACM2模拟海风偏强的原因是其边界层垂直混合偏强,形成了足够的湍流混合强度所致。对于边界层高度的模拟,ACM2的边界层顶最高,这与此方案所模拟的海风强度偏大相吻合,其它方案的边界层高度与海风强度并不完全一致。      

Time domain method for calculating free field motion of a layered half-space subjected to obliquely incident body waves

In numerical simulation of wave scattering under oblique incident body waves using the finite element method, the free field motion at the incident lateral boundary induced by the background layered half-space complicates the computational area. In order to replace the complex frequency domain method, a time-domain method to calculate the free field motion of a layered half-space subjected to oblique incident body waves is developed in this paper. The new method decouples the equations of motion used in the finite element method and offers an interpolation formula of the free field motion. This formula is based on the fact that the apparent horizontal velocity of the free field motion is constant and can be calculated exactly. Both the theoretical analysis and numerical results demonstrate that the proposed method offers a high degree of accuracy.