Ion dynamics associated with substorm dipolarization fronts

We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts(DFs) in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by multiple THEMIS spacecraft in the near-Earth magnetotail(~?10 Re). We studied the ion dynamics associated with these DFs by comparing observed results with large scale kinetic(LSK) simulation results. The LSK simulation reproduced the sudden ion energy flux enhancement concurrent with the arrival of the DF at the satellite locations. We found that ions can be accelerated to more than 100 keV energy at the DF. These ions were initially non-adiabatically accelerated near magnetic reconnection site and then still non-adiabatically accelerated at the DF structure.     

Analytical solutions for benchmarking cold regions subsurface water flow and energy transport models: One-dimensional soil thaw with conduction and advection

Numerous cold regions water flow and energy transport models have emerged in recent years. Dissimilarities often exist in their mathematical formulations and/or numerical solution techniques, but few analytical solutions exist for benchmarking flow and energy transport models that include pore water phase change. This paper presents a detailed derivation of the Lunardini solution, an approximate analytical solution for predicting soil thawing subject to conduction, advection, and phase change. Fifteen thawing scenarios are examined by considering differences in porosity, surface temperature, Darcy velocity, and initial temperature. The accuracy of the Lunardini solution is shown to be proportional to the Stefan number. The analytical solution results obtained for soil thawing scenarios with water flow and advection are compared to those obtained from the finite element model SUTRA. Three problems, two involving the Lunardini solution and one involving the classic Neumann solution, are recommended as standard benchmarks for future model development and testing.     

二阶Born近似有限频率走时敏感核

有限频率层析成像考虑了非均匀介质中波的散射、衍射、波前愈合等物理性质,使得其对速度异常体的分辨能力远大于射线层析成像.推导和计算有限频率敏感核是进行有限频率层析成像的关键,当前推导有限频率敏感核多借助一阶Born近似,但这只适用于弱散射介质的情况.本文基于二阶Born近似并利用傅里叶变换推导了三维均匀介质情况下有限频率敏感核的解析表达式,并将其推广到非均匀介质中得到了三维非均匀介质中有限频率敏感核.研究表明:当介质中速度扰动小于2%时,基于二阶Born近似的有限频率敏感核与基于一阶Born近似的有限频率敏感核差别很小,可近似认为相同;当介质中速度扰动大于5%时,基于二阶Born近似的有限频率敏感核与基于一阶Born近似的有限频率敏感核有较大不同,表明此时已不能忽略二次散射.     

CR-InSAR与PS-InSAR联合解算方法及在西秦岭断裂中段缓慢变形研究中的应用

本文结合CR-InSAR、PS-InSAR技术,将CR、PS点联合构网,采用LAMBDA方法进行相位解缠,研究西秦岭北缘断裂带中断的微小形变,结果得出断裂带表现出左旋走滑运动特征,断裂带南盘平均形变速率为2.3mm·a~(-1),北盘平均形变速率为-1.5mm·a~(-1),南北两盘平均形变速率差异为3.8mm·a~(-1),与其他学者GPS、地质测年研究成果相近.对研究区内的角反射器(CR点)安装、影像特征分析及形变解算进行了较为详细的论述,并对比分析了CR、PS点联合构网和PS点单独构网解算结果,得出对地质环境复杂的断裂带做永久散射体形变研究时,CR、PS点联合构网解算结果好、研究结果可靠.说明CR、PS点联合构网中,CR点由于其自身的高稳定特性,对整个解算网络起到了很好的整体控制作用,保证了解算结果正确.     

北天山山前地带垂直形变特征及其与地震的关系

根据垂直形变资料分析，北天山山前地带的垂直形变具有继承性运动特征，天山山体继续上升，盆地继续下降，在空间上具有统一性，在时间上具有同步性。１９８０年天山北缘石河子南５．８级地震，震前的正向加速形变转为反向形变，为预报北天山地震带的强震提供了时间依据；反向形变异常最大的地段，是未来发生强震的可能地点。     

Morphology and Chemistry of Placer Gold from Attappadi Valley, Southern India

We report the morphological, textural and chemical characteristics of gold grains in stream gravels from the Siruvani River in Attappadi Valley, southern India. The placer gold deposits contain both primary grains with jagged grain contours and secondary grains with smooth grain margins. The primary and secondary gold grains are also distinguished by marked contrast in microtextures with the latter displaying a range of corrosion textures including striations, etch pits and chemical corrosion cavities that coalesce to form honey-comb patterns. Some of these cavities are filled with fine clay derived from lateritic weathering front. While the primary grains are characterized by high silver content (up to 35.77 wt.%) with marginal overgrowths of high purity gold, the secondary grains show exceedingly high fineness (1000 Au/Au+Ag) levels (up to 984) with no marked compositional variation indicating selective extraction of Ag and/or reprecipitation of Au. From morphological and chemical characteristics, we propose that the high purity gold grains were not derived directly from primary sources, but underwent chemical refinement in the weathering front before they were transferred to the fluvial systems. Our findings have important implications for gold exploration in the Attappadi Valley.     

非地转湿Q矢量的改进及其应用

在完全考虑非绝热加热项作用的前提下,从原始方程出发,推导出改进后的非地转湿Q矢量(Q^q),以及用其散度作强迫项的ω方程,将其应用于一次梅雨锋暴雨诊断分析,结果表明:改进后的非地转湿Q矢量对同时刻地面降水的反映能力较岳彩军改进的湿Q矢量(Q^M)、原非地转湿Q矢量(Q^*)、非地转Q矢量(Q#)有显著的提高;在整个梅雨锋暴雨过程中,500hPa高度上的Q^q矢量散度辐合场的辐合强度及其辐合中心位置对同时刻的降水强度及雨区位置有非常好的指示作用;Q^q矢量的垂直分布揭示了次级环流的方向和强弱,暴雨位于次级环流的上升支附近。     

Sensitivity of the equatorial air—sea coupled system to the zonal phase difference between SST and wind stress

An eigen analysis of the equatorial air-sea coupled model is carried out to understand the mechanism of the slowly varying mode for various zonal phase differences between SST and wind stress. The frequency and growth rate of the slow mode highly depend on the zonal phase difference between SST and wind stress anomalies and the wave scale. For ultra-long waves longer than 20,000 km, the system propagates westward regardless of the position of wind stress. However, for the long waves observed in the Pacific, the slow mode tends to propagate eastward when the SST and wind stress anomalies are close to each other (within a quadrature phase relationship). On the other hand, when the wind stress is located far away from SST, the slow mode tends to propagate westward. The coupled system produces the unstable modes when the westerly (easterly) wind stress is located in the west of warm (cold) SST. It is noted that for the Pacific basin scale,the eastward propagating unstable waves can be produced when the wind stress is located to the west of SST with a few thousand kilometer distance. Also examined in the present study is the relative role of the thermocline displacement and zonal advection effects in determining the propagation and instability of the coupled system.     

2014年4月22日新疆寒潮天气过程锋面结构演变特征分析

中亚是寒潮强冷空气爆发的关键区,天山陡峭高大地形阻挡了冷气团前锋面系统的东移南下的移动,呈准静止状态,在中亚强天气中扮演着重要角色,目前研究不多。本文选取2014年4月22日08时开始北疆发生大风降温,南疆发生强沙尘暴的一次寒潮天气过程,利用常规气象观测数据和分辨率为1o×1o的NCEP再分析资料,分析了这次寒潮天气锋面过程的500 hPa天气形势和地面气压场形势;计算了和锋面密切相关的冷暖平流、温度梯度和锋生函数;分析了三个物理量在水平面以及西北东南向的垂直剖面上的三维立体结构和演变特征。研究表明： 500 hPa东欧脊在暖平流作用下快速发展,西西伯利亚槽在冷平流作用下加强并东移南下。受其影响,中亚地区地面图上锋面气旋发展旺盛,地面冷锋在东移过程中遇到平均海拔高度3000m的天山高大陡峭地形,温度梯度增大,产生较强的锋生。该锋面在对流层中下层的水平面图上表现为等位温线沿天山密集分布,位温梯度很大;在垂直剖面上,在天山位置表现为锋生,等位温线变为准垂直分布,梯度增大,宽度变窄。     

北太平洋冬季天气尺度涡旋的机理分析

利用1981~2013年NOAA（美国国家大气海洋管理局）海温资料和NCEP（美国环境预报中心）大气再分析资料,采用经验正交函数（EOF）分解方法对850 hPa瞬变高度场进行分解发现:850 hPa瞬变高度场经验正交函数分解的前两模态表征同一发展型波动的传播特征,该波动在日本以西形成然后向东发展,沿东偏北移动,在日界线附近发展达到最强,之后迅速向东北衰弱直至消亡,本文将其定义为西部型天气尺度涡旋（WSE）。合成分析表明,西部型天气尺度涡旋的强弱变化与北太平洋大范围的海温、副极地海洋锋异常存在密切联系,当西部型天气尺度涡旋活动偏强时,北太平洋北部和中部的海温显著偏冷,副热带地区海温显著偏暖,副极地海洋锋大大增强。同时,西部型天气尺度涡旋的强度与大气环流异常存在明显的协同变化,表现为西部型天气尺度涡旋偏强对应于阿留申低压增强且位置偏东,中纬度上空纬向西风增强。海洋和大气环流的这种变化增强了西北太平洋上空大气的斜压性,使得有效位能向扰动动能的转换增加,从而有利于西部型天气尺度涡旋的发展。