应用于L波段风廓线雷达的2 kW限幅器设计

边界层风廓线雷达为气象预报服务提供垂直性、连续性、高时空分辨率的探测数据。针对在全国各雷达站集中式雷达运行过程中限幅器频繁烧毁导致雷达停止工作的问题,设计了一种L波段2kW高功率无源限幅器。此款限幅器在电路前端引入双耦合电缆和功率电阻,增加了散热能力,一分为二限幅,使通过PIN二极管的功率降低一倍,电路后端多级二极管并联,逐级平缓限幅;具有承受功率高,限幅电平低,插入损耗小的特点。利用ADS软件进行仿真,并对限幅器进行了测试,结果表明各项指标满足设计要求。此款限幅器在边界层风廓线雷达上的应用,极大地提高了雷达稳定性。     

干旱区盐碱尘暴的形成、输送及其环境效应

盐碱尘暴是富含细粒硫酸盐和氯化物的化学尘暴,是大气颗粒物PM10的重要来源之一。盐碱尘暴的产生、输送和沉降对区域甚至全球生态环境和气候变化具有重大影响。本文分析了盐碱尘暴的化学组成及其危害,对盐碱尘暴的形成、输送及其环境效应作了研究综述。结果表明：干旱区干涸湖床是盐碱尘暴的发源地,风蚀作用下干涸湖床盐粒和粉尘的扩散过程主要受风场、区域气候特征和地下水埋深的影响。构建综合风动力和下垫面因子的盐粒风蚀物扩散模型,加强盐分风—水两相运移耦合作用及其与流域景观变化的关系研究是盐碱尘暴的突破方向。     

基于模糊逻辑的风廓线雷达功率谱数据质量控制研究

随着风廓线雷达组网观测系统建设的推进,质量控制是提高风廓线雷达观测资料应用效益的重要环节。通过介绍风廓线雷达回波信号的产生机理、信号与数据处理流程,研究了风廓线雷达多普勒功率谱的湍流回波与干扰回波的特征,给出了功率谱的特征量,提出了基于模糊逻辑提取大气湍流回波信息的质量控制方法,改进了多普勒速度估算的准确性。为检验质量控制方法的可靠性,以合肥2008年6月4日10:42:16(北京时,下同)东波束和8日10:36:20西波束的多普勒功率谱数据处理为例开展了风廓线观测资料质量控制的个例试验分析,结果表明处理后观测资料的可用性较好。     

风电场两种超短期风速预报方法的效果对比

针对风电场所需的时效在0~4 h,且时间分辨率不低于15 min的超短期风速预报。根据测风塔实时发回的实测风速序列,建立了基于BP神经网络的风电场风速时间序列外延预报模型。另一方面,建立 MM5模式预报风速与实测风速的误差序列,并利用BP神经网络作误差序列的外延预报,从而利用误差的预报值对MM5风速预报值进行订正,获得新的预报值。综合对两种方法的预报效果指标分析以及拟合曲线的比较结果表明:使用BP神经网络对MM5风速预报值进行修订的方法在总体上效果较优,特别是当影响风电场的天气系统变化明显,近地层风速变率较大时,该方法的预报效果更具有明显的优势。     

Three-dimensional simulations and wind-tunnel experiments on airflow over isolated forest stands

Prediction of windthrow risk to individual or groups of retained trees in harvested stands requires an improved understanding of canopy airflow dynamics. Large-eddy simulations were used to simulate wind-tunnel experiments in two and three dimensions to compare with observations for model validation and to address parameter space considerations for the design of subsequent retention pattern experiments. The three-dimensional simulations were similar to the observed wind-tunnel data for the statistical profiles for but there were greater differences in skewness and kurtosis. These results were obtained using a common leaf-area drag formulation without either skin friction or speed dependent drag that enables scaling with U ₀ (ambient wind speed) and h (height of the canopy). This scaling results in a single non-dimensional parameter h/h _c where h _c (x, y, z) is the momentum range resulting from the canopy drag. The validity of the model scaling was tested using two-dimensional simulations. The irrotational component of the flow (potential flow) was found to be important when defining vertical domain limitations and has significant implications for time dependent flow (i.e. turbulent conditions) when considering retention pattern design. The sudden onset of drag associated with the isolated stand presents some unexpected challenges. The horizontal scales of the shearing instabilities were simulated in two dimensions and found to range between 2h for early times to 7h for later times. The early-time horizontal scales are in the range of logical retention pattern scales and as such need to be taken into account as part of the parameter space, i.e. a range of retention pattern lengths need consideration.     

基于World Wind的鄱阳湖水位动态变化仿真系统研究

World Wind是由美国宇航局(NASA)开发的三维地理信息系统,也是一款可提供丰富数据的数字地球平台,如何将多源数据实现紧密型二三维耦合是基于World Wind开发专业系统需要解决的重要问题.在.NET开发环境下,以World Wind为仿真内核,开发了水位仿真系统,研究了二三维数据耦合技术,实现了环鄱阳湖生态经济开发区的湖区与航道淹没分析和三维漫游.结果表明,仿真系统流畅地实现了任意点地形高程、水位、水深和航道级别等信息的实时查询,仿真了不同控制水位条件下的鄱阳湖区淹没范围,仿真结果能够服务于鄱阳湖水利枢纽的水位调控决策;该仿真系统在湖泊干旱特征水位等确定中也具有重要的应用价值.     

Temporal characteristics and fog water collection during summer in Tenerife (Canary Islands, Spain)

The study of fog dynamics in the island of Tenerife began in 1993 at six sites. The analysis of the relationship between fog and several meteorological parameters was conducted at the site located at Anaga. Anaga is located at the summit of a mountain range, at an altitude of 842 m and 3.5 km away from the north-western coastline of the island. The study uses hourly data of the three summer months (June, July and August) that were collected over a period of nine years — from 1996 to 2005. The mean summer (June–August) rainfall was found to be 21.2 mm whilst the total volume of fog water collected was 879.9 l m^− 2; the daily average fog water collection was 9.5 l m^− 2 day^− 1, and the hourly average about 0.4 l m^− 2 h^− 1. Although these amounts were recorded with wind speeds of between 8 and 12 m s^− 1, the correlation between water collected and wind speed is not statistically significant. In spite of this, the volume of fog water collected and wind speed showed a very distinct daily behavioural pattern, their frequency and speed reaching their minimum at 12 a.m. and their maximum from 7 p.m. to 8 a.m. GMT. The importance of this research is that it shows that the fog in the Canary Islands occurs more frequently and makes a more significant contribution to the growth of vegetation in the summer (the dry season) than in the winter, when fog accompanies rainfall.     

风能模拟系统WEST在中国风能数值模拟中的应用

利用加拿大风能资源数值模拟系统(WEST)进行中国风能资源的模拟,得到了水平分辨率5km、低空垂直分辨率10 m的中国风能分布图谱。将模拟结果与气象台站观测资料进行了对比分析,结果表明,WEST在中国中东部海拔较低地区的模拟能力较好,平均相对误差<20%,但对于中国西部高原的模拟结果不理想,相对误差达到了60%以上,说明WEST系统对中国西部高原的模拟能力还需提高。应从其大尺度气候背景场分类和中尺度模型大气边界层物理过程参数化方面进行本地化改进,使之能更好地应用于中国风能资源评估工作。     

用双多普勒天气雷达资料研究暴雨三维风场结构

使用双多普勒天气雷达三维风场反演技术对2005年6月11-12日梅州和汕头多普勒天气雷达探测到的华南暴雨资料进行了三维风场反演,对暴雨系统的中尺度三维动力结构进行了详细分析.结果表明:此次暴雨主要是由中低层的中β尺度辐合线、中β尺度切变线和嵌于其中的中γ尺度涡旋共同作用引发的.低层辐合、高层辐散的动力结构,有利于暴雨系统的触发、维持和发展.最后,综合分析结果给出了此次暴雨的三维动力结构模型.