应用PIV系统研究横流中近壁水平圆柱绕流旋涡特性

应用粒子图像测速(PIV)系统对横流中近壁水平圆柱绕流进行了试验研究。介绍了试验原理及装置,讨论了试验参数的选取和粒子的跟随性问题。分析了上游来流的流动特性,显示了亚临界雷诺数下间隙比为0.5时圆柱后尾流区旋涡产生、发展和消亡的动态过程,比较了时均流场和瞬时流场旋涡结构。对圆柱尾迹的旋涡脱落特性进行了分析,得出在试验条件下斯特劳哈尔数保持为常数0.2的结论。     

近六百年来长江三角洲地区城镇空间与城镇体系格局演变分析

基于历史文献、古地图和现代遥感数据,引入历史学古代城镇形态复原方法,复原（提取）明代以来长江三角洲地区113座城镇7个时间断面（1461年、1820年、1930年、1970年、1980年、2000年和2010年）下的城镇边界,采用扩张速率、扩张效率、首位度指数和位序-规模法则,分析了近六百年来区域城镇空间与城镇体系等级规模演变格局。取得以下研究结果：\mathrm{①}研究时段内,区内城镇用地总规模由205.98 km²增加到6442.19 km²,扩大了31.27倍;城镇扩张经历了萌芽阶段（明清时期）、起步阶段（民国至改革开放前夕）、成长阶段（改革开放至2000年）和加速阶段（2000—2010年）,城镇扩张速率不断加快,但扩张效率有待提升;\mathrm{②}在城镇等级规模空间格局上,明清时期南京与苏州为区内的一级城镇,民国后,上海逐渐取代其地位,从五级城镇发展成为区域核心城镇,四级以上城镇主要集中在长江干流沿岸和太湖流域,五级以下城镇大多集中在安徽;城镇体系呈首位型分布,城镇首位度较高,且改革开放后的城镇首位度较明清与民国时期要高,不同等级规模城镇之间差距扩大,大城镇优势较强。近30年,长江沿岸城镇发展加速,苏锡常都市圈、南京都市圈等逐渐形成并快速发展。     

Inland saline lakes with lagoonal biota: some reflections on the concept and nature of athalassic (non-marine), paralic and marine saline waters

First, some inland basins with lagoonal (or paralic) biota are brieffly described. The different kinds of saline aquatic environments are then defined and the composition of their biota are discussed. Finally, the still unknown microbiogeochemical composition of concentrated inland waters is discussed. Under arid and endorheic conditions, it seems that the wider and the more geologically complex a hydrological basin is, the more biogeochemically similar to seawater is the water of its terminal lake. The evolution of the microbiogeochemical complexity of seawater through geological times is considered.This paper has been the subject of considerable discussion among referees. Not all of the views expressed by the author are accepted by them.     

Climate change of the last millennium inferred from borehole temperatures: regional patterns of climatic changes in the Czech Republic — Part III

Accurate temperature–depth profiles may help to assess the temperature variations associated with the climate changes in the past. Ninety-eight ground surface temperature histories inverted from the temperature–depth borehole logs drilled on the territory of the Czech Republic [Bodri, L., ermák, V., 1995. Climate changes of the last millennium inferred from borehole temperatures: results from the Czech Republic — Part I. Global Planet. Change 11, pp. 111–125; Bodri, L., ermák, V., 1997. Climate changes of the last two millennia inferred from borehole temperatures: results from the Czech Republic — Part II. Global Planet. Change 14, pp. 163–173.] are used to reconstruct the regional patterns of the respective climate change. The climate was mapped for the following periods: 1100–1300 A.D. (Little Climatic Optimum), 1400–1500 A.D., 1600–1700 A.D. (main phase of the Little Ice Age), and for the most recent climate trend after year 1960. Comparison of the obtained maps with the meteorological observations and proxy climatic reconstructions confirmed good applicability of the “geothermal” paleoclimatic reconstructions for the regional studies.     

Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China

Short sediment cores retrieved from Bosten Lake, the largest inland freshwater lake in China, were used to explore humidity and precipitation variations in arid central Asia during the past millennium. The chronology of the cores was established using 137Cs, 210Pb and AMS 14C dating re- sults. Multi-proxy high-resolution analysis, including pollen ratios of Artemisia and Chenopodiaceae (A/C), carbonate content and grain size, indicates that the climate during the past millennium can be divided into three stages: a dry climate between 1000―1500 AD, a humid climate during the Little Ice Age (LIA) (c. 1500―1900 AD), and a warm dry period after 1900 AD. On centennial timescales, the climate change in northwestern China during the past 1000 years is characterized by oscillations between warm-dry and cold-humid climate conditions. All the proxies changed significantly and indi- cate increased precipitation during the LIA, including increased pollen A/C ratios and pollen concen- trations, decreased carbonate content and increased grain size. The humid period during the LIA re- corded by the Bosten Lake sediments is representative of arid central Asia and is supported by nu- merous records from other sites. During the LIA, the water runoff into the Keriya River and Tarim River in the Tarim Basin increased, while the ice accumulation in the Guliya ice core increased. Additionally, the lake levels of the Aral and Caspian Sea also rose, while tree-ring analysis indicates that precipita- tion increased. We hypothesize that both the lower temperature within China and the negative anomalies of North Atlantic Oscillation (NAO) during this period may have contributed to the humid climate within this area during LIA.     

全球过去千年典型暖期温度空间格局重建

利用过去两千年全球变化研究网络(PAGES 2k network)最新公布的501条代用记录,重建了全球过去千年全年平均温度空间格局的演化特征,对比分析了中世纪暖期及其最暖100年与20世纪现代暖期、中世纪暖期和小冰期最暖30年与20世纪最近30年的年平均温度空间模态异同.结果显示,在世纪尺度上,现代暖期与历史上中世纪暖期的温度异常空间格局大致相同,变化幅度也在大部分区域相当,但从年代际尺度上,最近30年的升温比过去千年中世纪暖期和小冰期两个典型时期都明显.值得一提的是北大西洋中高纬度海温变化与上述特征并不相同,在年代际和世纪尺度上小冰期和中世纪暖期海温均高于20世纪.可能原因是大西洋经圈翻转环流在中世纪暖期、小冰期和20世纪现代暖期等3个特征时段对太阳辐射、火山活动和温室气体等外强迫的响应不同.     

过去2000年全球典型暖期特征与机制的模拟研究

本文利用美国国家大气研究中心(NCAR)的通用地球系统模式(Community Earth System Model,简称CESM)的低分辨率版本(CESM1.0.3,T31_g37)在国际国内率先进行了多组过去2000年瞬变积分模拟试验,在与历史重建资料和观测资料进行对比验证的基础上,对过去2000年中的典型暖期(中世纪暖期与现代暖期)的特征和成因机制进行了初步探讨,结果表明:中世纪暖期太阳辐射加强是导致其“暖化”的主要原因之一,而温室气体浓度的激增是现代全球变暖的最主要原因;在中世纪暖期,自然因子(包括太阳辐射和火山活动)对降水量的影响之和比温室气体的影响高一个数量级;而在现代暖期,温室气体对降水量的影响比自然因子(包括太阳辐射和火山活动)对降水量的影响之和高一个数量级;在不同外强迫条件下的海表温度变化在热带太平洋区域截然不同,即自然因子影响下为类-拉尼娜态,而温室气体影响下为类-厄尔尼诺态;无论在中世纪暖期还是现代暖期,相对于1000～1850年的平均情况,沃克(Walker)环流均处于增强状态.     

过去百年青海和西藏耕地空间格局重建及其时空变化

网格化的历史土地利用/覆被数据集,可为历史气候变化和碳循环研究提供基础数据。本文估算了1910年,并订正了1950-2000年青海和西藏的省域耕地面积数据;基于现代耕地空间格局,量化了海拔高程和地面坡度与耕地空间分布之间的关系,构建了历史耕地网格化重建模型。将1910、1960、1980和2000年的省域耕地面积数据带入网格化重建模型,得到了4个时间断面的耕地空间格局。结果表明:青藏两省耕地面积1910-1950年稳定,1950-1980年快速增加,1980-2000年基本稳定,略有降低。就空间格局而言,1960-1980年,河湟谷地和"一江两河"地区土地开垦范围的扩张和垦殖强度的增长在过去百年最为明显。模型检验表明,模型重建的2000年耕地空间格局与2000年遥感数据相关系数达0.92。     

呼和浩特市近50a气温变化特征分析

利用呼和浩特市1961—2010年气温资料,用线性回归、方差分析等统计方法分析呼市气温的年代际变化特征以及季节性变化规律,指出近50a来平均气温以每0.57℃/10a的幅度增高。     

A View of Earth System Model Development

This paper gives a definition of earth system model and shows three development phases of it, including physical climate system model, earth climate system model, and earth system model, based on an inves- tigation of climate system models in the world. It provides an expatiation on the strategic significance of future development of earth system model, an introduction of some representative scientific research plans on development of earth system model home and abroad, and a review of its status and trends based on the models of the fourth assessment report （AR4） ofthe Intergovernmental Panel on Climate Change （IPCC）. Some suggestions on future development of earth system model in China are given, which are expected to be helpful to advance the development.