广东省大冰雹事件的层结特征与融化效应

本文主要利用L波段常规探空数据、华南区域加密自动站资料以及ERA-Interim 0.125°×0.125°逐6 h再分析资料,依据我国冰雹等级划分标准（GB/T 27957-2011）筛选了2004～2017年发生在广东的23个大冰雹事件（直径≥20 mm）,重点分析其大气层结状态与结构特征,定量诊断了大冰雹的融化效应,并建立了判别大冰雹的物理参数模型。结果表明:（1）大冰雹事件“上干下湿”比非大冰雹（直径≥5 mm且＜20 mm）事件更加清晰,产生大冰雹所需的对流（位势）不稳定建立更依赖于“上干下湿”而不是“上冷下暖”。（2）H_?/H₊（冷云和暖云厚度比值）对于区分大冰雹与非大冰雹具有较好的指示效果,H_?/H₊高于1.6/1对判别产生大冰雹有参考价值。（3）相比于非大冰雹事件,大冰雹事件最大热浮力高度高于?5℃层,有利于托举雹胚进入有效增长层（?10℃～?30℃）,促使雹胚生长为大冰雹。最大热浮力强度≥4℃可作为判别大冰雹与非大冰雹的关键阀值。（4）热传递与对流交换（）对大冰雹融化起主要作用,其贡献率与DBZ（冻结层高度）、（环境平均温度）呈反比关系;冰雹表层水膜因蒸发或重新凝结消耗潜热（）对大冰雹融化影响表现在DBZ高度上的冰雹直径越小、融化贡献率越大,大冰雹融化程度越大。高空的干层向下延伸到较低高度有利于大冰雹不被或少被融化,也是大冰雹事件WBZ（湿球零度层高度）显著低于DBZ的重要原因。（5）基于全文统计内容与对比分析,构建了一个判别大冰雹的物理参数模型,大气层结满足ΔT_d85（850 hPa与500 hPa的露点差）≥46℃、500 hPa的T?T_d≥15℃、1000～700 hPa最小的T?T_d≤2℃、H_? /H₊≥1.6/1,最大热浮力强度≥4℃、最大热浮力高度高于?5℃层时,有利于产生大冰雹。     

Analysis of Deformation of Adjacent Buried Pipeline Under Rockfall Impact Load

Geotechnical and Geological Engineering - The current research on the deformation of buried pipeline under rockfall impact load is generally based on the analysis of the pipeline cross-sectional...     

顾及城乡差异的大区域人口密度估算——以山东省为例

现有大区域人口密度估算结果大多是在千米级尺度上,仅能宏观地反映城乡人口分布的范围,无法准确地刻画城乡人口空间分布的细节特征。本文将首套30m全球地表覆盖数据(GlobeLand30)引入城乡人口密度估算中,基于实现城乡划分的GlobeLand30人造地表数据,在城镇区域运用夜间灯光强度与人口的相关性将城镇人口细划到30m尺度上来估算城镇人口密度;在乡村区域引入样方估算的方法修正乡村居民地面积以估算乡村人口密度。以山东省为试验区的研究表明,本文方法无论在城乡居民地刻画还是人口空间分布的表达上均优于参考数据,所使用的GlobeLand30的全球性也保证了该方法推广的可行性。     

Neighborhood-scale urban form,travel behavior,and CO2 emissions in Beijing: implications for low-carbon urban planning

With an increasing awareness of global climate change, the effect of urban spatial organization, at both city and neighborhood scales, on urban CO₂ emission reduction has attracted much scholarly and practical attention. Using Beijing as a case study, this article examines the extent to which neighborhood-scale urban form may contribute to reduction of travel-related CO₂ emissions in the context of rapid urbanization and spatial transformation. We derive complete travel-activity records of 1,048 residents from an activity diary survey conducted in 2007. Analysis using structural equation models finds that residents living in a neighborhood with higher land use mix, public transit accessibility, and more pedestrian-friendly street design tend to travel in a “low-carbon” manner and emit less CO₂ in daily travel, even controlling for residential and travel preferences. This article offers empirical evidence that sheds light on debates about policy measures to facilitate China’s transition toward sustainable and low-carbon urban development.     

中国西南—东南季风交汇区降水时空格局变化及其对食物产量的影响

全球气候变化背景下,降水格局改变食物供给将是人类当前和未来所面临的重大挑战,但很少有研究揭示食物供给随降水格局变化的关系。研究中国西南、东南季风共同作用区的降水与食物供给变化,对厘清该区降水与食物供给的动态关系、实现区域粮食安全、保障西南边疆稳定、落实区域民族政策、建成全面小康社会等具有重要意义。文章以中国西南地区的云南省为例,刻画了1988—2018年降水变化格局,并探讨了其对食物产量的影响。结果表明：① 云南省降水时间格局分为：Ⅰ降水丰沛期（1988—2004年）、Ⅱ降水偏少期（2005—2015年）、Ⅲ降水恢复期（2016—2018年）等3个降水时段;② 第Ⅰ~Ⅱ时段,全省降水发生显著变化区域为15.07%,第Ⅱ~Ⅲ时段为13.87%,第Ⅰ~Ⅲ时段为16.53%;③ 全省水平上,降水与食物产量具有显著正相关关系（p<0.01）,且粮食产量与各时间段降水相关系数高于肉奶产量;④ 当降水≥1500 mm时降水量快速下降,粮食产量保持稳定、700~1500 mm时降水量与粮食产量同为小幅下降、≤ 700 mm时降水量小幅下降,粮食产量大幅波动下降。总体而言,1988—2018年云南省降水格局发生了明显的变化,且在不同区域对食物供给产生了显著影响,故亟待划分全省范围的食物产量对降水响应的空间区划,以此来应对日益加剧的降水格局变化。     

Empirical determination of geometric parameters for selective omission in a road network

Selective omission in a road network is a necessary operation for road network generalization. Most existing selective omission approaches involve one or two geometric parameters at a specific scale to determine which roads should be retained or eliminated. This study proposes an approach for determining the empirical threshold for such a parameter. The idea of the proposed approach is to first subdivide a large road network, and then to use appropriate threshold(s) obtained from one or several subdivisions to infer an appropriate threshold for the large one. A series of experiments was carried out to validate the proposed approach. Specifically, the road network data for New Zealand and Hong Kong at different scales (ranging from 1:50,000 to 1:250,000) were used as the experimental data, and subdivided according to different modes (i.e. administrative boundary data, a regular grid of different sizes, different update years, and different road network patterns). Not only geometric parameters, but also structural and hybrid parameters of existing selective omission approaches were involved in the testing. The experimental results show that although the most appropriate thresholds obtained from different subdivisions are not always the same, in most cases, the appropriate threshold ranges often overlap, especially for geometric parameters, and they also overlap with those obtained from the large road network data. This finding is consistent with the use of different subdivision modes, which verifies the effectiveness of the proposed approach. Several issues involving the use of the proposed approach are also addressed.     

地图信息论:从狭义到广义的发展回顾

地图是人类认识客观世界的有力工具。地图的核心功能是传输空间信息。自20世纪60年代源自通信领域的信息论被引入地图信息度量.现代地图学已经发展了一个崭新的研究领域——地图信息论。本文旨在对近50年来地图信息论的发展历程进行回顾,论述从狭义到广义地图信息论的基本概念、研究进展及应用领域,最后对地图信息论的发展进行了展望。     

How many samples are needed? An investigation of binary logistic regression for selective omission in a road network

ABSTRACT

Selective omission in a road network (or road selection) means to retain more important roads, and it is a necessary operator to transform a road network at a large scale to that at a smaller scale. This study discusses the use of the supervised learning approach to road selection, and investigates how many samples are needed for a good performance of road selection. More precisely, the binary logistic regression is employed and three road network data with different sizes and different target scales are involved for testing. The different percentages and numbers of strokes are randomly chosen for training a logistic regression model, which is further applied into the untrained strokes for validation. The performances of using the different sample sizes are mainly evaluated by an error rate estimate. Significance tests are also employed to investigate whether the use of different sample sizes shows statistically significant differences. The experimental results show that in most cases, the error rate estimate is around 0.1–0.2; more importantly, only a small number (e.g., 50–100) of training samples is needed, which indicates the usability of binary logistic regression for road selection.     

遥感及其地球表面时空多变要素的区域尺度转换

阐明了遥感在获取时空多变要素中的作用和意义,同时利用遥感方法作出了空间变异较大的叶面积指数、地表温度和净辐射通量的区域分布。通过遥感方法与传统的区域表达方法的对比,讨论了传统的等值线方法及其区域要素计算和表达方法的不足,估算了利用空间差异较大的非均匀要素所作出的区域分布的可能误差。其步骤是： ①用遥感和生态网络观测数据相结合的方法作出几个要素的区域分布影像图; ②在影像图上标出单点生态站的观测数据; ③以图像处理的方法,作出不同范围的各种要素平均值和标准差; ④揭示单点站的观测数据和不同范围要素平均值的差异; ⑤分析用传统的等值线方法所作出的区域分布的可能误差。     

Climate Change,Geopolitics, and Human Settlements in the Hexi Corridor over the Last 5,000 Years

Social responses to climate change over human history have been widely discussed in academia over the last two decades. However, the transformation of the human–environment nexus crossing prehistoric and historic periods and the processes associated with it are not yet clearly understood. In this study, based on published works on radiocarbon dating, archaeobotany, zooarchaeology, and archaeological sites, together with a synthesis of historical documents and highresolution paleoclimatic records, we trace the extent to which human settlement patterns in the Hexi Corridor in northwestern China evolved in conjunction with climate change over the last 5,000 years. A total of 129 Neolithic, 126 Bronze Age, and 1,378 historical sites in the Hexi Corridor(n=1,633) were surveyed. Our results show that, in the Late Neolithic and Bronze Age periods(～2800–100 BC), climate change contributed to the transformation of subsistence strategies and the subsequent changes in human settlement patterns in the Hexi Corridor. The warm-humid climate in ～2800–2000 BC promoted millet agriculture and helped the Majiayao, Banshan, and Machang Cultures to flourish. The cold-dry climate in ～2000–100 BC resulted in the divergence and transformation of subsistence strategies in the Xichengyi–Qijia–Siba and Shajing–Shanma Cultures and in a shift in their settlement patterns. However, in the historical period(121 BC–AD 1911), human settlement patterns were primarily determined by geopolitics related to the alternating rule of regimes and frequent wars, especially in the Sui–Tang dynasties. We also find that trans-Eurasian cultural exchange since ～2000 BC improved social resilience to climate change in the Hexi Corridor, mediating the human–environment nexus there. Our findings may provide insights into how human societies reacted to climate change in arid and semi-arid environments over the long term.