"2004.6"湘西北低空急流暴雨的中尺度分析

利用常规观测,T213、雷达和MM5中尺度模式输出资料对2004年6月23-24日湘西北地区的暴雨和大暴雨进行了天气动力学和中尺度分析.结果表明这场暴雨是在有利的天气背景条件下产生的,造成强降水的雨团在时空尺度上具有中尺度系统的特征,中尺度辐合线和低空急流为降水发生提供了有利的触发条件.     

长江三角洲地区对流层臭氧的变化趋势

Analysis of tropospheric ozone residual (TOR) data from satellite measurements indicates an increasing trend of tropospheric ozone over the Yangtze Delta region of China. The increasing trend can be derived both from the annual mean TOR and from the monthly mean TOR except for January and March. The increase rate of the decadal mean TOR was 0.82 DU during 1978-2000. The impact of this long-term trend on the climate and atmospheric oxidizing capacity over the region should be further studied. Data comparison shows a significant correlation between the TOR and surface ozone data collected at Lin'an background station in the Yangtze Delta region, suggesting an internal connection between both quantities.     

Integrated Navigation System and Experiment of a Low-Cost and Low-Accuracy SINS/GPS

When SINS (strap-down inertial navigation system) is combined with GPS, the observability of the course angle is weak. Although the course angle error is improved to some extent through Kalman filtering, the course angle still assumes a divergent trend. This trend is aggravated further when using low-cost and low-accuracy SINS. In order to restrain this trend, a method that uses AHRS to substitute for SINS course angle information is put forward aimed at the hardware component characteristic of the low-cost and low-accuracy SINS including AHRS (attitude and heading reference system) and IMU (inertial measurement unit). Real static and dynamic experiments show that the method can restrain the divergent trend of the navigation system angle effectively, and the positioning accuracy is high.     

计算机地貌晕渲效果增强方法研究

在总结传统手工晕渲经验和方法的基础上，深入分析了计算机地貌晕渲的原理，着重研究了坡度和坡向对地貌晕渲中阴影强弱和明暗程度的影响，提出了变比例调整高程和晕渲笔调调整两种方法。实验表明，利用本文方法能有效改善地貌晕渲图的三维立体视觉效果。     

An Improved Hilbert Curve for Parallel Spatial Data Partitioning

A novel Hilbert-curve is introduced for parallel spatial data partitioning, with consideration of the huge-amount property of spatial information and the variable-length characteristic of vector data i...     

基于ArcGIS的时空数据库的设计与实现

一般的数据库基本上不存储旧的、过时的数据，而时空数据库则包括任何历史数据，使数据库可以成为任何一个系统和部门的完整的电子信息档案库。本文通过基于ArcGIS基础空间数据库的建库，运用ArcGIS的历史归档机制，探索出一套时空数据库的设计与实现方案。     

影响自动站传输率的故障分析及处理

从自动站参数设置、值班人员要求和网络等方面分析影响自动站传输率的原因,提出注意事项。     

Climate change and critical thresholds in China’s food security

Identification of ‘critical thresholds’ of temperature increase is an essential task for inform policy decisions on establishing greenhouse gas (GHG) emission targets. We use the A2 (medium-high GHG emission pathway) and B2 (medium-low) climate change scenarios produced by the Regional Climate Model PRECIS, the crop model – CERES, and socio-economic scenarios described by IPCC SRES, to simulate the average yield changes per hectare of three main grain crops (rice, wheat, and maize) at 50 km × 50 km scale. The threshold of food production to temperature increases was analyzed based on the relationship between yield changes and temperature rise, and then food security was discussed corresponding to each IPCC SRES scenario. The results show that without the CO₂ fertilization effect in the analysis, the yield per hectare for the three crops would fall consistently as temperature rises beyond 2.5 ^{^}C; when the CO₂ fertilization effect was included in the simulation, there were no adverse impacts on China’s food production under the projected range of temperature rise (0.9–3.9 ^{^}C). A critical threshold of temperature increase was not found for food production. When the socio-economic scenarios, agricultural technology development and international trade were incorporated in the analysis, China’s internal food production would meet a critical threshold of basic demand (300 kg/capita) while it would not under A2 (no CO₂ fertilization); whereas basic food demand would be satisfied under both A2 and B2, and would even meet a higher food demand threshold required to sustain economic growth (400 kg/capita) under B2, when CO₂ fertilization was considered.     

Multi-scale analysis of global temperature changes and trend of a drop in temperature in the next 20 years

Summary A novel multi-timescale analysis method, Empirical Mode Decomposition (EMD), is used to diagnose the variation of the annual mean temperature data of the global, Northern Hemisphere (NH) and China from 1881 to 2002. The results show that: (1) Temperature can be completely decomposed into four timescales quasi-periodic oscillations including an ENSO-like mode, a 6–8-year signal, a 20-year signal and a 60-year signal, as well as a trend. With each contributing ration of the quasi-periodicity discussed, the trend and the 60-year timescale oscillation of temperature variation are the most prominent. (2) It has been noticed that whether on century-scale or 60-year scales, the global temperature tends to descend in the coming 20 years. (3) On quasi 60-year timescale, temperature abrupt changes in China precede those in the global and NH, which provides a denotation for global climate changes. Signs also show a drop in temperature in China on century scale in the next 20 years. (4) The dominant contribution of CO₂ concentration to global temperature variation is the trend. However, its influence weight on global temperature variation accounts for no more than 40.19%, smaller than those of the natural climate changes on the rest four timescales. Despite the increasing trend in atmospheric CO₂ concentration, the patterns of 20-year and 60-year oscillation of global temperature are all in falling. Therefore, if CO₂ concentration remains constant at present, the CO₂ greenhouse effect will be deficient in counterchecking the natural cooling of global climate in the following 20 years. Even though the CO₂ greenhouse effect on global climate change is unsuspicious, it could have been excessively exaggerated. It is high time to re-consider the trend of global climate changes.     

大型沉水植物狐尾藻不同盖度的光谱特征

地物特征与其光谱特征的关系是解译遥感影像的关键。本研究利用ASD便携式地物光谱仪对上海崇明国际湿地公园人工湖中的沉水植物狐尾藻的反射光谱进行了初步研究。结果表明,随狐尾藻盖度的增加,其光谱反射率、一阶和二阶导数红边斜率的峰值也相应增加,不同盖度狐尾藻的光谱反射率的差异主要表现在500—650nm和700—900nm波段范围。分别对狐尾藻盖度与这些波段的光谱反射率及根据一阶和二阶导数获得的光谱指数进行回归分析,得到了较好的线性关系。应用回归分析得到的线性方程,可以根据测定的光谱反射率定量反演水体中的狐尾藻盖度。研究结果可为监测大型沉水植物的高光谱遥感影像解译和分类提供技术支撑,为大尺度遥感监测沉水植物的分布和动态变化提供科学依据。