The importance of local‐scale openness within regions dominated by closed woodland     

Ralph Fyfe 《第四纪科学杂志》2007,22(6):571-578

New and existing pollen data from Wales, UK, are used to assess the level of landscape openness at the regional and local scale. At the regional scale, the existing pollen data support the high‐forest model of vegetation structure by 6000 cal. yr. BC prior to any palynological signal for anthropogenic impact in the region. New data from two sites in southwest Wales follow the general regional pattern of early to middle Holocene vegetation succession, but are striking owing to maintenance of high non‐arboreal pollen percentages (NAPs) throughout the mid‐Holocene. It is argued that these NAPs indicate that a significant degree of openness can be found at the local level (and beyond the confines of the peat‐forming site) within regions characterised by closed woodland. It is possible that woodland development in these areas may have been suppressed by reduced drainage, although the role of grazing animals in maintenance of clearings cannot be assessed. Implications for this local degree of openness are discussed, in particular the significance of vegetation heterogeneity at the local scale for the construction of place or locale for prehistoric communities. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Fine-resolution simulation of surface current and sea ice in the Arctic Mediterranean Seas   总被引：1，自引：0，他引：1  

刘喜迎  张学洪  宇如聪  刘海龙  李薇 《中国海洋湖沼学报》2007,25(2):132-138

A fine-resolution model is developed for ocean circulation simulation in the National Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Chinese Academy of Sciences, and is applied to simulate surface current and sea ice variations in the Arctic Mediterranean Seas. A dynamic sea ice model in elastic-viscous-plastic rheology and a thermodynamic sea ice model are employed. A 200-year simulation is performed and a dimatological average of a 10-year period (141st-150th) is presented with focus on sea ice concentration and surface current variations in the Arctic Mediterranean Seas. The model is able to simulate well the East Greenland Current, Beaufort Gyre and the Transpolar Drift, but the simulated West Spitsbergen Current is small and weak. In the March climatology, the sea ice coverage can be simulated well except for a bit more ice in east of Spitsbergen Island. The result is also good for the September scenario except for less ice concentration east of Greenland and greater ice concentration near the ice margin. The extra ice east of Spitsbergen Island is caused by sea ice current convergence forced by atmospheric wind stress.  相似文献   

An assessment of arctic sea ice concentration retrieval based on “HY-2” scanning radiometer data using field observations during CHINARE-2012 and other satellite instruments     

SHI Lijiang  LU Peng  CHENG Bin  KARVONEN Juha  WANG Qimao  LI Zhijun  HAN Hongwei 《海洋学报(英文版)》2015,(3)

A retrieval algorithm of arctic sea ice concentration (SIC) based on the brightness temperature data of “HY-2” scanning microwave radiometer has been constructed. The tie points of the brightness tempe...  相似文献   

北京市平原区2015年—2019年0.8 m地表反射率数据集     

申茜  姚月  李利伟  龙腾飞  陈甫  张兵 《遥感学报》2021,25(11):2303-2312

地表反射率产品作为最重要的定量遥感产品,是很多参量化遥感产品的基础数据源,可以被广泛应用于林业、农业、水资源、生态环境、城市环境等典型应用领域。对于米级高分辨率的遥感影像,国内外不提供反射率影像产品。目前主流的国产高分数据源大部分都是蓝、绿、红、近红4个波段的多光谱数据,缺少短波红外波段,难以满足陆地区域浓密植被算法或者清洁水体的短波红外信号近似看作零的假设条件,要完成精确大气校正、生产大范围的GF-2影像拼接的地表反射率产品,是一个挑战。为了更好的推广高分地表反射率的应用,本研究针对北京市平原区,运用全色和多光谱融合、几何精校正和相对辐射一致化算法,以Sentinel-2为参考影像,生成了一套几何精校正后的0.8 m地表反射率影像集。该数据集时间范围为2015年—2019年,每年一期,包含年度产品的覆盖情况及分布矢量,共计184景地表反射率影像,数据量总共为1.63 TB。  相似文献   

Impact of the Vertical Velocity Field on Charging Processes and Charge Separation in a Simulated Thunderstorm          下载免费PDF全文

WANG Fei  ZHANG Yijun  ZHENG Dong  XU Liangtao 《Acta Meteorologica Sinica》2015,29(2):328-343

A three-dimensional(3D) charging-discharging cloud resolution model was used to investigate the impact of the vertical velocity field on the charging processes and the formation of charge structure in a strong thunderstorm. The distribution and evolution of ice particle content and charges on ice particles were analyzed in different vertical velocity fields. The results show that the ice particles in the vertical velocity range from 1 to 5 m s-1obtained the most charge through charging processes during the lifetime of the thunderstorm. The magnitude of the charges could reach 1014 n C. Before the beginning of lightning activity,the charges produced in updraft region 2(updraft speed 13 m s-1) and updraft region 1(updraft speed between 5 and 13 m s-1) were relatively significant. The magnitudes of charge reached 1013 n C, which clearly impacted upon the early lightning activity. The vertical velocity conditions in the quasi-steady region(updraft speed between –1 and 1 m s-1) were the most conducive for charge separation on ice particles on different scales. Accordingly, a net charge structure always appeared in the quasi-steady and adjacent regions. Based on the results, a conceptual model of ice particle charging, charge separation, and charge structure formation in the flow field was constructed. The model helps to explain observations of the"lightning hole" phenomenon.  相似文献   

基于贝叶斯融合方法的高分辨率地面-卫星-雷达三源降水融合试验   总被引：15，自引：1，他引：14  

潘旸  沈艳  宇婧婧  熊安元 《气象学报》2015,73(1):177-186

为了探讨一种适用于区域性的地面、雷达、卫星等多源降水资料融合的方法,一种曾用于高分辨雷达、卫星土壤湿度产品反演的贝叶斯融合(Bayesian Merging)方法被尝试应用于江淮地区1 h-0.05°×0.05°经纬度高分辨率的雷达估测降水、卫星反演降水与地面站点观测降水3种资料的融合。在应用该方法时,通过2009年8月样本统计分别估计卫星和雷达反演降水的误差关系,通过曲线拟合建立误差方程,并以卫星资料作为背景场,但在融合时将雷达估测降水作为新的观测信息与地面观测降水同时引入。融合试验检验结果表明:贝叶斯融合方法能够有效实现雷达、地面、卫星3种不同来源资料的融合,该方法生成的多源融合产品的精度均优于任何单一来源的降水产品。  相似文献   

HYSPLIT模式轨迹计算误差分析     

马玉芬  陆辉  刘海涛 《南京气象学院学报》2015,7(1):86-91

基于NCEP 1°×1°再分析资料GDAS和NCEP2.5°×2.5°再分析资料GBL,利用美国NOAA 空气资源实验室ARL研发的一种用于计算和分析大气污染物输送、扩散轨迹的混合单粒子拉格朗日综合轨迹模式HYSPLIT,对2010年3月12日12时和田站距地100 m高度空气质点的3 d前向轨迹进行了模拟,分析了轨迹计算中的积分误差和分辨率误差.此次轨迹模拟试验中,积分误差对轨迹计算误差的贡献很小.随着积分时间的延长,积分误差略有增大.积分误差并未随着驱动数据分辨率的提高而减小.分辨率误差在积分的各个时刻并不相同,它与地形高度与天气系统有关.在轨迹模式中,轨迹计算基于风速在时间和空间上的线性插值,轨迹模拟的不确定性也与插值有关.使用不同分辨率的驱动数据对轨迹计算结果影响显著,分辨率误差对轨迹计算误差的贡献远大于积分过程中截断近似等带来的积分误差.  相似文献   

European Solar Telescope: Progress status     

M. Collados  F. Bettonvil  L. Cavaller  I. Ermolli  B. Gelly  A. Prez  H. Socas‐Navarro  D. Soltau  R. Volkmer  the EST team 《Astronomische Nachrichten》2010,331(6):615-619

In this paper, the present status of the development of the design of the European Solar Telescope is described. The telescope is devised to have the best possible angular resolution and polarimetric performance, maximizing the throughput of the whole system. To that aim, adaptive optics and multi‐conjugate adaptive optics are integrated in the optical path. The system will have the possibility to correct for the diurnal variation of the distance to the turbulence layers, by using several deformable mirrors, conjugated at different heights. The present optical design of the telescope distributes the optical elements along the optical path in such a way that the instrumental polarization induced by the telescope is minimized and independent of the solar elevation and azimuth. This property represents a large advantage for polarimetric measurements. The ensemble of instruments that are planned is also presented (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

世界各国日像仪主要性能比较     

姬国枢  王威  何俊波 《天文研究与技术》2010,7(2)

本文是世界各国日像仪的天线阵性能汇集,包括日、俄、法、中、美等专用日像仪及美国、印度、巴西等兼作日像仪的天线阵,列出了几个典型天线阵列排列及接收系统。附录中列出了等口径及不等口径天线阵列的灵敏度及动态范围计算公式,同时列出了视场、角分辨率等公式。便于读者自行分析,计算,比较各天线阵列性能。  相似文献   

面元细分处理资料的分辨率定量评价     

徐辉  张军华 《物探化探计算技术》2010,32(1):59-63

以永新工区高精度采集的地震资料为例,对高精度勘探的面元细分方法及细分处理资料的分辨率进行了评价。首先给出了面元细分的方法及面元细分对地震资料分辨率的影响,介绍了现有的一些分辨率计算方法。对于纵向分辨率,主要从λ/4传统薄层分辨率和高截频二个方面进行了讨论;对于横向分辨率,从菲涅耳带半径、防空间假频、Lindsey分辨率定义、考虑偏移孔径的分辨率等四个方面进行了分析、比较。通过研究,得出了有一定借鉴意义的结论:①在现有常规检波器条件下,面元细分处理对地震资料的分辨率影响较小,其变化不大;②在单道记录信噪比已较高的情况下,想通过提高覆盖次数来提高资料的分辨率,其提升空间有限;③就横向分辨率而言,考虑偏移孔径的计算方法,结果比较准确;④对于东部地区,从性价比上考虑,覆盖次数150,200已能满足要求,太高的覆盖次数没有从本质上改进资料的质量。  相似文献