Barrier destruction and Lagrangian predictability at depth in a meandering jet

Numerical simulations of a jet with large amplitude meanders are used to explore chaotic advection processes and underlying geometry changes as functions of the ambient potential vorticity gradient β. Variations in β in the 2D model qualitatively simulate changes in depth in 3D, surface-intensified jets such as the Gulf Stream. As β is reduced, corresponding to motion on increasingly deep isopycnal surfaces, a number of geometrical transitions take place in the flanges and across the core of the jet. The most important is a joining (or separatrix reconnection) of heteroclinic cat’s eyes structures lying to the north and south of the jet core. The jet core acts as a barrier to transport, but this barrier is breached when the cat’s eyes merge. The subsequent chaotic transport across the jet is demonstrated by calculations of effective invariant manifolds (EIMs) originating in hyperbolic regions to the north and south of the core. Destruction of the central barrier occurs as β is lowered through a narrow window W about β=0 and is marked by transitions form a meandering jet through a vortex street with no central meandering flow to a vortex street with a retrograde meander. Such small values of β are deemed reasonable in view of measurements of low potential vorticity gradients in the deep Gulf Stream. The strength of the central barrier for β outside W is tested by varying β about a mean value β₀ and detecting the minimum amplitude of fluctuation necessary for destruction of the barrier. It is found that the barrier is stronger for β₀>0, at least by this measure. A striking difference is that, for β<0, some disturbances may destroy the barrier without oscillating across W; whereas for β>0, destruction of the barrier may only occur when β passes through W. Changes in underlying geometry also occur in the flanges of the jet and these changes alter the locations in which fluid is preferentially stirred and mixed. Float trajectories can be regular or irregular depending upon where the instrument is launched and this is demonstrated by plotting trajectories from inside and outside regions of chaotic advection.     

改革开放二十年来中国城市地理学研究进展

改革开放２０ａ来,中国城市地理学研究队伍不断壮大,研究领域不断向纵深拓展,新技术在城市研究中获得了广泛应用。对这一时期中国城市地理学的研究进展,研究方法和技术作了综述,并对其发展趋势做了展望。     

Global airline networks and nodal regions

Transportation infrastructure has always played an important role in the economic fate of regions. In particular, airline networks have dramatically decreased the geographic and temporal constraints of moving people, goods and information; all of which are increasingly crucial inputs for the information economy. As a result, regions have become more concerned with both the quantity and quality of airline connections. The purpose of this paper is to examine the emerging global hierarchy of airline network connectivity. Using a proprietary database of nearly 900 airline carrier schedules from 2006, we examine regional connectivity between 4,650 worldwide origins and destinations. Through the use of network analysis and graph theoretical techniques, results indicate an increasingly complex web of nodal hierarchies in North America, Europe and Asia.

战略耦合演化视角下的区域经济韧性分析框架

在全球政治经济变局和多尺度危机冲击语境下,区域经济韧性已成为当下经济地理学探究区域发展动态的核心议题。区域经济韧性不仅有关本地经济属性和适应力,更受到外部联系动态的影响,在范式上需融入多尺度网络动态观。本文将全球生产网络理论中的战略耦合概念纳入到演化经济地理学的区域经济韧性思想中,对两部分文献进行计量分析和梳理对比。在此基础上,以战略耦合不同模式（即耦合、去耦合、再耦合）为切入点,构建了一套基于“战略耦合演化”的区域经济韧性分析框架。研究结论：① 任何一种战略耦合模式,均是一种“战略性求变”和“语境应对”的能动行为过程,是理解区域经济韧性尺度性与能力来源的核心。② 两者在“连接度”“语境敏感性”“路径发展”概念上有较高的思想共性,相互融合可提升区域经济韧性的理论内涵。③ 战略耦合的能动主体、目的、嵌入性程度及方式是理解区域经济韧性特征和机制的关键,有助于从“地方-全球连接互动”的视角来综合分析区域经济韧性的初始属性（区域优势）、过程（恢复、更新和转型）、能力（恢复力、转型力和更新力）和结果（多元路径发展趋势）。本文认为战略耦合演化视角有利于破除以往“区域主义”韧性思想,能更科学地剖析区域经济韧性的多尺度语境依赖、多主体能动过程和多要素互动机制。此外,有利于推动关系与演化经济地理范式的融合创新,对“双循环”战略下中国企业决策和区域经济发展有重要现实意义。     

张其昀主编的《方志月刊》及其地理学贡献

《方志月刊》是中国近代唯一的一种侧重于区域地理的刊物,刊物的名称选择、编辑特色等均受到了主编张其昀地理学思想的影响。通过对《方志月刊》载文及相关史实的梳理与考证,解析其办刊特色和地理学贡献。研究表明：该期刊注重科学的区域地理研究和地图、照片的运用,注重国外地理学成果的介绍和地理学史的整理,为中国近代地理学特别是区域地理学的发展提供了有益导向。     

Application of Visual MODFLOW to simulation of migration in Cr6+ contaminated site

On the basis of site investigation and data collection of a certain electro plating factory, the groundwater flow and solute transport coupled models were established by applying Visual MODFLOW 4.1 software, which was used to conduct a numerical simulation that forecast the transport process of Cr6+ in groundwater. The results show that contamination plume of Cr6+ transports with groundwater flow direction. Without control measures, in 3 650 days, 19 wells for drinking would be contaminated, and the range of transport would be 52 172 m2, the maximum contamination would be 35.8 mg/L     

当前国外政治地理学边境安全研究进展

如何在边境地区最大限度地实现人流、物流和资金流等自由、快速的有效流动,从而促进国家经济快速发展的同时,防止国际犯罪集团、恐怖主义、非法移民、毒品和大量破坏性武器通过边境地区进入本国,以保证边境和国家的安全,已经成为各国对边境安全研究的核心。当前围绕这一主题国外政治地理学对边境安全的研究主要集中在：对边境安全研究的基本理论探讨、自由贸易与边境安全、恐怖主义与边境安全和先进技术应用与边境安全等4个方面。文章在梳理这4个专题已有研究的基础上,总结了今后边境安全需要进一步深入探讨的基本问题：1）边境安全的理论与实践之间的不一致性;2）高新技术在边境安全管理中的应用;3）边境安全管理中的双边合作;4）边境安全预警体系构建。最后,提出了国外边境安全研究对中国边境安全的一些启示。     

中国大陆地区生态诅咒效应的多尺度实证检验

基于生态系统服务理论界定生态福祉概念及其表征、评价方法,借鉴资源诅咒理论,提出广义生态福祉视域下的生态祝福及生态诅咒假说,结合有关年度统计数据、以中国大陆地区为例展开实证分析。结果表明：① 从人均生态福祉来看,全国范围内的绝对生态诅咒假设不成立,东、西部地区生态祝福效应显著;② 从农林牧渔产业从业人员比例来看,全国及地区层面的条件生态诅咒假设均不成立,东部地区生态祝福效应显著;③ 从农林牧渔产业产值比例来看,全国及地区层面的条件生态诅咒假设均显著成立。自然生态系统为提高区域人均生态福祉、吸纳富余劳动力就业等贡献显著,但促进地区经济社会发展还需不断降低农林牧渔产业产值在国民经济中的比例。未来,中国应当进一步实施因地制宜的生态保护措施以规避生态诅咒,并通过因时制宜的经济社会发展规划促进生态祝福效应。     

西宁市典型污染日PM10输送规律研究

为研究西宁市PM₁₀的区域性污染特征,对2006年3月至2010年2月各季逐日大气污染指数（API,首要污染物为PM₁₀）进行统计分析。利用后向轨迹模型（HYSPLIT Model）对西宁市典型污染日（API > 200）中气团的后向轨迹进行模拟,研究PM₁₀的运动轨迹和区域性污染的可能来源。结果表明：西宁市一年中春季（集中于3月和4月）PM₁₀污染严重,与该季节气团对颗粒物的长距离输送有关。造成西宁市重污染状况的主要天气是风沙尘,北部和西北部的沙漠地区是主要风沙源;相邻城市PM₁₀污染峰值的提前与滞后,体现出区域性污染的传输过程。     

国家1∶50000基础地理信息数据库更新工程及实施

国家1∶50 000基础地理信息数据库更新工程是我国"十一五"初启动的重点测绘工程,历经5年多实现了对1∶50 000数据库的全面更新。本文重点介绍了更新工程的背景、主要内容、技术方法、组织实施及其所取得的主要成果。