A comparison of MODIS-derived cloud amount with visual surface observations   总被引：6，自引：0，他引：6  

Andrzej Z. Kotarba   《Atmospheric Research》2009,92(4):522-530

Two main sources for global cloud climatologies are visual surface observations and observations made by spaceborne sensors. Satellite observations compared with surface data show in most cases differences ranging from − 15% up to − 1%, depending on sensor and observation conditions. These differences are partially controlled by sensors' cloud detection capabilities — a higher number of spectral bands and higher spatial resolution are believed to allow discrimination of clouds from land/ocean/snow background. A Moderate-Resolution Imaging Spectroradiometer (MODIS) produces images of the atmosphere in 36 spectral bands with a spatial resolution of 250–1000 m, thus having a capacity for cloud detection far more advanced than other operating sensors. In this study, instantaneous MODIS cloud observations were compared with surface data for Poland for January (winter) and July (summer) 2004. It was found that MODIS observed 4.38% greater cloud amount in summer conditions and 7.28% in winter conditions. Differences were greater at night (7–8%) than in daytime (0.5–7%) and correlations ranged between 0.577 (winter night) and 0.843 (winter day, summer day and night).  相似文献   

Laboratory experiments on along-slope flows in homogeneous and stratified rotating fluids     

D.L. Boyer  D. Sous  J. Sommeria 《Dynamics of Atmospheres and Oceans》2009,46(1-4):19-35

Laboratory experiments have been carried out for the flow along isobaths of simulated shelf-continental slope geometry. Cases of both homogeneous and linearly stratified fluids are considered and the background flows are sufficiently strong to have the flow near the bottom boundary range from transitional to fully turbulent. The background motions are impulsively started and flows with a coast on the right (spin-down) and on the left (spin-up) are considered. The homogeneous spin-down and spin-up processes are smooth in the sense that no vortical structures were found to be of the order of the slope width or larger. Flows reach equilibrium more quickly for spin-down cases, and this is attributed to secondary flows forced by the basin geometry. All of the stratified experiments exhibited large-scale instabilities as evidenced by the generation of slope and basin scale eddy structures and a much slower decay than their homogeneous counterparts.  相似文献   

The Impact of Mid- and High-Latitude Rossby Wave Activities on the Medium-Range Evolution of the EAP Pattern During the Pre-Rainy Period of South China          下载免费PDF全文

SHI Ning  BUEH Cholaw  JI Liren  WANG Panxing 《Acta Meteorologica Sinica》2009,23(3):300-314

Based on the NCEP DOE AMIP II daily reanalysis data (1979{2005), the evolution of the East Asia/Pacific(EAP) teleconnection pattern during the pre-rainy period of South China is studied on the medium-range time scale. It is found that positive and negative EAP patterns share a similar generation process. In the middle and upper troposphere, Rossby wave packets emanating from the northeast Atlantic or Europe propagate toward East Asia along the Eurasian continent waveguide and finally give rise to the three anomaly centers of the EAP pattern over East Asia. Among the three anomaly centers, the western Pacific subtropical center appears the latest. Rossby wave packets propagate from the high latitude anomaly center toward the mid-latitude and the subtropical ones. The enhancement and maintenance of the subtropical anomaly center is closely associated with the subtropical jet waveguide and the incoming Rossby wave packets from the upstream. In the lower troposphere, Rossby wave packets emanate from the subtropical Asia toward East Asia. Positive and negative EAP patterns could not be regarded as "mirrors" to each other with simply re- versed phase. For the positive pattern, the positive height anomaly center around the Scandinavia Peninsula keeps its strength and position during the mature period, and the Rossby wave packets thus propagate persistently toward East Asia, facilitating a longer mature time of the positive pattern. As for the formation of the negative EAP pattern, however, the incoming Rossby wave energy from the upstream contributes to both the enhancement and southeastward movement of the negative anomaly belt from the Yenisei River to the Bering Strait and the positive anomaly center around Mongolia. At the peak time, the two anomlous circulations are evolved into the Northeast Asia and the mid-latitude anomaly centers of the negative pattern, respectively. The energy dispersion of Rossby wave packets is relatively fast due to the predominant zonal circulation in the extratropics, causing a shorter mature period of the negative pattern. During the pre-rainy period of South China, the prevalence of the EAP pattern signiˉcantly affects the rainfall over the region south of the Yangtze River. The positive (negative) EAP pattern tends to causepositive (negative) precipitation anomalies in that region. This is di?erent from the earlier research findingsbased on monthly mean data.  相似文献   

Effects of the low-frequency zonal wind variation on the high frequency atmospheric variability over the tropics     

K. P. Sooraj  Daehyun Kim  Jong-Seong Kug  Sang-Wook Yeh  Fei-Fei Jin  In-Sik Kang 《Climate Dynamics》2009,33(4):495-507

Recently, there is increasing evidence on the interaction of atmospheric high-frequency (HF) variability with climatic low-frequency (LF) variability. In this study, we examine this relationship of HF variability with large scale circulation using idealized experiments with an aqua-planet Atmospheric GCM (with zonally uniform SST), run in different zonal momentum forcing scenarios. The effect of large scale circulation changes to the HF variability is demonstrated here. The HF atmospheric variability is enhanced over the westerly forced region, through easterly vertical shear. Our study also manifests that apart from the vertical wind shear, strong low-level convergence and horizontal zonal wind shear are also important for enhancing the HF variance. This is clearly seen in the eastern part of the forcing, where the HF activity shows relatively maximum increase, in spite of similar vertical shear over the forced regions. The possible implications for multi-scale interaction (e.g. MJO–ENSO interaction) are also discussed.  相似文献   

CINRAD/SA雷达频综故障检修方法   总被引：3，自引：1，他引：2  

周红根  高玉春  胡帆  周良  蔡勤  吴田  兰杰 《气象》2009,35(10):113-118

频综是多普勒全相参天气雷达的核心部件,其组件工艺水平高且价格昂贵,它提供了整个雷达工作所需的基准信号,共有5路输出,它们分别是9.6MHz主时钟信号、COHO信号、RF DRIVE信号、STALO信号、RF TEST SIGNAL信号.由于不同地区雷达发射机工作频率不同,因此频综不能通用,在台站,备份频综组件不太现实.由于厂家没有提供频综图纸,使得故障判别难度加大.因此通过剖析频综内部结构,给出频综的内部原理简图.针对十多个CINRAD/SA雷达频综出现的故障,划分出三种故障类型,并提出具体维修方法,在此基础上,归纳出该型号雷达在使用过程中频综出现故障时,雷达操作、维护人员应掌握的故障排查方法及技巧,以提高台站的保障能力.  相似文献   

CINRAD/SA雷达开关组件故障分析处理   总被引：6，自引：4，他引：2  

吴少峰  胡东明  黎德波  郭泽勇  杨朝辉 《气象科技》2009,37(3):353-355

根据广州CINRAD／SA雷达发射机开关组件的一起故障现象,结合信号流程、电路原理图,深入元件一级,对故障的定位、检测及排除过程作了详细介绍,并对故障的成因作了推断分析,最后就雷达维护方面总结了一些经验,旨在对雷达技术保障人员提供参考和借鉴。  相似文献   

清洁发展机制（CDM）造林再造林项目碳汇成本研究——以CDM广西珠江流域治理再造林项目为例   总被引：1，自引：0，他引：1       下载免费PDF全文

张治军  张小全  朱建华  罗云建  侯振宏  褚金翔 《气候变化研究进展》2009,5(6):348-356

以清洁发展机制（CDM）广西珠江流域治理再造林项目为例,对项目及其5种造林模式临时核证减排量（temporary certified emission reduction,缩写为tCER）和长期核证减排量（long-term certified emission reduction,缩写为lCER）成本的动态变化进行了初步研究。结果表明：从项目期初到期末,整个项目及5种造林模式人工林的tCER成本均逐渐降低,其中项目成本由第一承诺期末的40.33 ￥/t CO₂降至最后承诺期末的13.34 ￥/t CO₂;lCER成本先降低后升高,在第一承诺期末均降至最小值,项目成本由第一承诺期末的40.33 ￥/t CO₂增加至最后承诺期末的105.27 ￥/t CO₂;各造林模式tCER和lCER成本均以枫香+杉木、枫香+马尾松较高,马尾松+荷木、马尾松+栎类较低,桉树最低;贴现率对项目tCER和lCER、桉树tCER、枫香+杉木lCER成本影响均较大,而对马尾松+栎类tCER和lCER成本影响均较小;对桉树一个轮伐期内的tCER成本进行了敏感性分析,单位面积碳贮量的变化对其影响较大;考虑木材收益时,项目期末tCER净现值为13.11 ￥/t CO₂,从中反映了该CDM项目实施是可行的。  相似文献   

从MODIS资料提取土壤湿度信息的主成分分析方法   总被引：2，自引：1，他引：1       下载免费PDF全文

周秉荣  李凤霞  申双和  胡玲 《应用气象学报》2009,20(1):114-118

沿袭了遥感地物分类中K-L变换思想, 以归一化处理后的遥感数据, 结合地面土壤湿度观测数据, 应用主成分分析方法, 采用MODIS不同红外波段数据, 通过相关关系计算, 在监测结果中融合MODIS具有250 m分辨率的第2波段数据, 建立了青海省多维特征空间土壤湿度监测模型。模型的建立克服了热惯量法监测干旱需多时相遥感数据的缺陷, 经初步检验, 此模型可以在一定精度范围之内监测表层土壤湿度, 具有业务应用潜力。  相似文献   

基于MODIS数据光谱突变法提取冬小麦种植面积研究   总被引：2，自引：0，他引：2  

王云峰  沈润平  田国珍 《内蒙古气象》2009,(6):18-21

利用2004—2005年MODIS 16天合成的NDVI最大值植被指数数据,基于NDVI光谱突变方法对山西省运城地区冬小麦种植面积提取。冬小麦有两个生育阶段其绿度—时相曲线与其他大宗作物、植被有明显差异：一是10—11月,为冬小麦秋播至分蘖阶段;二是5—6月,为冬小麦孕穗至收获期。通过分析得出：2005年5—6月（2005161～2005129）提取的冬小麦面积与实测面积相关性最高,估测的冬小麦面积与实测面积的误差最小,准确性最高。  相似文献   

2008年1月一次强雨雪过程的诊断分析     

朱坤  刘华强  刘宇丹  蒋坡   《气象与环境科学》2009,32(3):15-21

采用NCEP1°×1°客观再分析资料和常规观测资料,对2008年1月25—29日发生在长江中下游地区的强雨雪过程进行诊断分析,结果表明,低空急流与强雨雪有着密切关系,强雨雪的发生需具备一定的温度条件以及水汽场与动力场的耦合机制。对强雨雪过程的湿Q矢量诊断分析表明,700hPa湿Q矢量辐合区以及850hPa锋生函数正值区与强雨雪区对应较好,对雨雪天气的发生有着很好的指示意义。湿位涡特征分析表明,此次强雨雪过程发生在层结稳定的大气中且垂直涡度发展较强。  相似文献