三维社区建模与分析的共形几何代数方法

利用共形几何代数的多维统一表达与分析优势,研究了集成多源数据的三维社区统一建模与分析方法。构建了基于多重向量存储结构的社区场景整体建模流程,实现了CityGML、DXF等多源数据的导入与集成,并设计了基于共形几何代数的对象运动表达与插值方法。以德国Waldbruecke村为例的验证结果显示,基于共形几何代数的三维社区建模可以较好地表达复杂社区对象,并可以有效支撑几何度量、动态对象跟踪、运动轨迹重建等功能实现。     

High Asia cryospheric observation: a proposed network under Global Cryosphere Watch (GCW)

In coordination with Global Cryosphere Watch (GCW) initiated by World Meteorology Administration (WMO), a regional observation network is proposed based on existing stations/sites over High Asia and cryospheric elements required by GCW. Thus, High Asian Cryosphere (HAC) network is preliminary designed, composing of seven "supersites", each containing several reference sites. The network covers major mountain ranges in High Asia, such as East Tianshan, Qilian, Tanggula, Nyainqentanglha, Himalayas as well as the central and eastern Qinghai-Xizang (Tibet) Plateau. Although multiple cryospheric elements were observed at the existing HAC network, many others, which are required by Integrated Global Observation System-Cryosphere Theme (IGOS-Cryosphere), are not yet included. More comprehensive observations are necessary to be included into "supersites" of HAC, so that the basic requirements for validation of satellite data, assimilation and coupled regional models can be met.     

Hydrodynamic change recorded by diatoms in sediments of Liuxihe Reservoir, southern China

Diatoms are used widely for paleolimnological studies in lakes, but their use for studying the environmental history of reservoirs has not been tested extensively. Reservoirs have hydrodynamic characteristics intermediate between those of rivers and lakes. This study assessed the utility of diatom assemblages as recorders of long-term changes in hydrodynamics and spatial gradients in Liuxihe Reservoir, an impoundment in southern China. Four sediment cores were collected in the reservoir, from the riverine, transition and lacustrine zones. Each core was sectioned at 2-cm intervals to investigate the stratigraphic distribution of accumulated diatoms. Varve counting was used to develop a chronology for one of the cores. The unique characteristics of Liuxihe Reservoir, including its large size, great depth, long narrow morphology and strong thermal stratification for 10 months of the year, limit secondary sedimentation processes and preserve the varves, enabling development of an accurate chronology. Damming profoundly altered the physical environment of the former river, especially in the lacustrine zone, where the change is clearly illustrated by diatoms in the sediment. Diatom abundance increased as a consequence of nutrient enrichment after construction of the dam in 1958, but later decreased as the new impoundment stabilized. After damming, relative abundance of Cyclotella increased along with a simultaneous decrease of Navicula and Achnanthes in the lacustrine zone, most significantly in 1963, when Cyclotella replaced Navicula as the dominant genus. This switch was indicative of a general shift from a lotic to a lentic habitat. A longitudinal gradient was apparent in the patterns of sedimentation and diatom accumulation at different sites in the reservoir, with diatom abundance highest in the transition zone. In the long term, water discharge from the reservoir showed a weak, but significant negative correlation with diatom abundance in the lacustrine zone (r = −0.320, P = 0.03). In summary, diatom assemblages in the Liuxihe Reservoir sediments recorded past changes in hydrodynamics, suggesting that paleolimnological study of some impoundments is feasible.     

Application of a simple binary mixing model to the reconstruction of lead pollution sources in two Mississippi River floodplain lakes

A simple binary mixing model is used to determine the isotopic ratios of lead (Pb) pollution sources to a lake located near a smelter closed because of excessive Pb aerosols (Horseshoe Lake Madison County, Illinois, USA). As a control, we also examine a relatively unpolluted lake in a rural area of Southern Illinois (Horseshoe Lake Alexander County). Sediment cores were taken from both lakes and analyzed for Pb and Pb isotopes by ICP-MS. The mixing model shows that Madison County Horseshoe Lake had 3 different sources of Pb in its history. The first source is sediment from the Mississippi River with an intermediate ²⁰⁶Pb/²⁰⁷Pb ratio (1.223 ± 0.009) which dominates inputs in pre-settlement times. From 1750 to 1933, the source of pollution Pb has the high ²⁰⁶Pb/²⁰⁷Pb ratio (1.256 ± 0.005) characteristic of ore from the southeast Missouri Pb mines. The most recently deposited pollution Pb comes from a source with a low ²⁰⁶Pb/²⁰⁷Pb ratio (1.202 ± 0.005). This source is similar in isotopic composition to pollution Pb found by several other investigators in the Eastern US and probably represents the mixture of ores used in modern industrial processes. It is unclear from the isotopic composition whether this source at Horseshoe Lake is the local Pb smelter or vehicle exhaust. The sediment core from Horseshoe Lake, Alexander County, shows a less variable isotopic composition. The binary mixing model showed a source composition of 1.225 ± 0.003 before 1850 and 1.231 ± 0.003 after this date. The change does not indicate a pollution source, but may be a shift in the sources of natural sediment with slightly different isotopic ratios to the lake. Our results show the value of simple binary mixing models to reconstruct the isotopic composition of Pb sources to lakes.     

Sequence architecture and depositional evolution of the Ordovician carbonate platform margins in the Tarim Basin and its response to tectonism and sea‐level change

The sequence architecture and depositional evolution of the Ordovician carbonate platform margins in the Tarim Basin, China, were formed in response to the interplay of tectonism and sea‐level change, their history being documented by the integrated analysis of many seismic lines, drilling and outcrop data. The Ordovician carbonate system in the basin is divided into four composite sequences defined by major unconformities. Each sequence consists of a regional depositional cycle from transgression with an onlapping transgressive systems tract (TST) to regression with a prograding highstand systems tract (HST), and can be further subdivided into 10 third‐order sequences based on subordinate discontinuous boundaries at the carbonate platform marginal zones. Constrained by the marginal slope of the early‐rifted Manjiaer aulacogen, the carbonate platform margins of the Lower and Middle Ordovician that prograded eastward in an arcuate belt extending generally north‐south across the northern part of the basin. The development of the Tazhong uplift due to compression resulted in an extensive paleokarst hiatus between the Middle and the Upper Ordovician in the south‐central basin, and subsequently constrained the formation of a peninsula‐shaped carbonate platform whose margins were controlled by marginal thrust‐fault belts of the paleo‐uplift during the Late Ordovician. In the northern basin, the Late Ordovician carbonate platform margin developed around the marginal slope of the Tabei paleouplift. The transgressive–regressive cycles of the carbonate system are comparable and seem to have occurred simultaneously across the entire basin, suggesting that the cyclic sequence architecture was fundamentally controlled by eustatic fluctuations. Stacking patterns of the composite sequences varied due to the interplay between the accommodation produced by tectonism and sea‐level change, and the carbonate production rate. The reef–shoal facies complexes that developed along the platform margins, with paleokarst development at unconformities, constitute the major reservoir of large petroleum reserves in the basin.     

基于分区和多元数据的青藏高原温泉区域多年冻土分布研究

以野外勘探、室内理论分析与建模为主要研究方法,以数字高程模型(GDEM)和实测数据为基础进行统计分析,发现坡向对多年冻土分布具有重要影响。针对青藏高原温泉区域地形的复杂性,基于分区的方法将研究区分为平原区和山区两个地形区。对于平原区来说,考虑到苦海湖泊对多年冻土的影响,将苦海滩地单独划出并采用专家知识完成冻土制图,其余平原区采用建立的地温模型进行冻土制图;对于山区来说,通过定量化研究坡向对冻土地温的影响建立了基于坡向调整作用下的地温模型,应用此模型完成了山区的冻土分布图。以地温作为冻土类型划分的依据,分析了研究区域冻土的空间分布与特征,结果表明:多年冻土的分布面积为1 681.4km2,占整个区域的66.7%,其中,过渡型和亚稳定型多年冻土为主要多年冻土类型,两者占整个研究区域的50.8%,其次为不稳定型多年冻土(11.4%),稳定型和极稳定型多年冻土的面积比例相对较小(4.4%和0.2%)。从空间分布格局来看,冻土分布具有明显的垂直分带特征,随着海拔高度的升高,冻土地温逐渐降低,冻土类型依次经历季节冻土-不稳定型多年冻土-过渡型多年冻土-亚稳定型多年冻土-稳定型多年冻土-极稳定型多年冻土的变化。     

An analytical investigation of a sequence of unusual springtime ozone episodes over metropolitan Taichung in 2007

This study investigated the potential factors contributing to a series of ozone (O₃) episodes in the Taichung metropolis, which occurred during the first half of May 2007. Surface data of the meteorological parameters and air pollutant concentrations, supported by Taiwan Environmental Protection Administration, and vertical data monitored via tethersonde sampling were analysed. The analyses showed that local anthropogenic activities and physical factors such as the sea–air interaction were not the main factors contributing to the O₃ events. Excluding these potential causes, the results suggest that, during the aforementioned period, the stronger Mainland High and Pacific Low may have been responsible for the long-range transport of large quantities of O₃ from Mainland China to Taiwan. Furthermore, O₃ photochemical activity also played an important role in the O₃ episodes. The faster consumption of NO lead to a more rapid increase in the O₃ concentration.     

Detection of trends in precipitation extremes in Zhejiang, east China

Extreme weather exerts a huge impact on human beings and it is of vital importance to study the regular pattern of meteorological and hydrological factors. In this paper, a selection of seven extreme indices is used to analyze the trend of precipitation extremes of 18 meteorological stations located in Zhejiang Province, east China using the Mann–Kendall test. Then the precipitation trends in the plum season (from May to July) and typhoon season (from August to October) are studied separately. The results show that the precipitation trend varies from east to west. There is a positive trend in the east and a negative one in the west. The largest part of Zhejiang Province shows a positive trend in heavy precipitation and the most significant upward trend is detected in Dinghai with 3.4?mm/year for precipitation on very wet days. Although the upward trend of extreme precipitation is not prevailing, the range of increase in specific areas is apparent, like Dinghai with 1.3?mm/year. Precipitation intensity exhibits an upward trend in most areas and a typical upward trend can be found in Dachendao, Tianmushan, and Yuhuan with 0.04, 0.02, and 0.05?mm/year respectively. Precipitation intensity in both plum and typhoon seasons has increased too, especially for the coastal stations.     

东太平洋冷舌区海表面温度日变化特征的模拟研究

本文通过分辨太阳辐射日变化, 利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室 (LASG/IAP) 气候系统海洋环流模式 (LICOM), 模拟了东太平洋冷舌区海表面温度 (SST) 的日变化特征并研究了弱混合对其影响。采用理想的太阳辐射日变化强迫上层垂向分辨率为10 m的海洋模式LICOM, 模拟出了SST日变化一些特征, 同时海洋的上层流场也产生明显日变化。模拟的SST日变化振幅水平分布与观测接近, 且受太阳辐射日变化振幅水平分布调制。在赤道中东太平洋区, 模拟的SST日变化振幅 (约为0.3～0.4℃) 比观测偏小约0.1～0.2℃。模拟的SST日变化峰值出现在15～16 时 (当地标准时间), 落后于太阳辐射峰值2～3个小时, 接近观测。进一步减弱混合后, 模拟的日变化振幅增加约0.1℃, 更接近观测。这说明在东太平洋冷舌区SST日变化主要受太阳辐射日变化和垂直混合影响。此外, 混合减小后, 在太阳辐射日变化调制下, 平均态 (如混合层、温度和流场) 也出现明显变化。在赤道东太平洋冷舌区北侧, 弱混合导致混合层变浅, 变浅使热量堆积进而使平均SST升高约0.3℃; 在赤道东太平洋冷舌南侧, 经向平流加强导致平均SST降低约0.2℃。     

大气本底站反应性气体观测数据处理系统功能设计及实现

基于反应性气体多年观测的较为成熟的数据处理和质量控制方法,采用模块化功能结构设计,通过应用Visual Studio开发平台并结合MAP WinGIS等空间和时间显示控件,对反应性气体观测数据处理系统进行了设计和开发.系统实现了观测数据在空间和时间上的可视化显示,实际业务应用表明,具有良好的人机交互和数据处理能力,具备一定的数据统计分析功能.实现了对大气本底站反应性气体观测数据的统一管理和综合处理,已成为大气成分观测数据质量控制业务系统的一个重要组成部分.