长江中下游旱涝中期预报方法及其业务应用   总被引：1，自引：1，他引：1  

金荣花  李月安  晁淑懿  任金声 《气象》2004,30(12):47-52

介绍了双层多因子综合相似的长江中下游旱涝中期预报模型。该模型引入了具有明确动力学和热力学意义的地转西风动量经向输送和经向温度梯度诊断量，同时强调了西太平洋副热带高压对长江中下游夏季降水的关键作用，并考虑了对流层中、低层500hPa高度和850hPa温度的大尺度环流背景场。与过去业务应用的单层相似预报模型相比较，不仅物理意义和天气学含义明确，而且更符合对具有复杂动力和热力机制的降水预报的考虑。5年的预报试验和业务应用结果表明，该方法对长江中下游地区旱涝的中期趋势预报有较好的预报能力。  相似文献   

基于GIS的地下水水源地补给潜力探讨     

叶超  李宇  田茂勇 《水文地质工程地质》2005,32(1):67-69

本文提出了一种基于GIS的补给潜力分析方法。在实例研究中,通过对地形、地表物质组成、包气带岩性、植被覆盖等因子建立的专题图层的叠加分析,确定了地下水的补给潜力分区,结合研究区含水层分布特征,综合确定了水源地的靶区和开采潜力区。研究表明,利用GIS确定研究区降雨入渗补给量是一种高效、直观、可行的方法。  相似文献   

Selective feeding of bay scallop Argopecten irradians on phytoplankton community revealed by HPLC analysis of phytopigments in Bohai Sea,China     

JIANG Tao  WANG Longhua  ZHANG Fuchong  FANG Xiao  LU Lin  ZHANG Jihong  WANG Wei  QU Keming  CHAI Chao 《中国海洋湖沼学报》2019,(5)

Understanding the feeding selectivity on phytoplankton by shellfish is currently a big challenge.In order to investigate the feeding behavior of bay scallop(Argopecten irradians)on phytoplankton,we compared its compositions of phytopigments in digestive glands with those in the surrounding seawater,and conducted five consecutive investigations between July and November 2016 in a bay scallop culture area along coast of Qinghuangdao City,northwest of the Bohai Sea,China.Phytopigments in four-size fractionated phytoplankton of seawater(micro-(20-200 μm);nano(L)-[10-20 μm];nano(S)-[2.7-10 μm],and pico-[2.7 μm])and digestive glands of A.irradians were examined to investigate the selective feeding of A.irradians.Results show that fucoxanthin and peridinin constituted the major part of taxonomically diagnostic carotenoids(TDCs)in the micro-and nano(L)-phytoplankton in seawater.Compared with total phytoplankton biomass of seawater(TPB,sum of the four sizes),a substantial decrease of fucoxanthin proportion to total DCs in digestive glands was observed while that of peridinin,19'-butanoyloxyfucoxanthin,alloxanthin and 19'-hexanoyloxy-fucoxanthin showed an obvious increase when those pigments were mainly confined to micro-sized phytoplankton(20-200 μm).However,zeaxanthin and prasinoxanthin were mainly confined to nano(s)-and pico-phytoplankton,of which the proportions in digestive glands were usually lower in TPB.The contribution of lutein to total DCs in digestive glands(with an average of 7.23%)increased compared with TPB of seawater(with an average of 0.63%)during all five sampling times.  相似文献   

2001-2015年中国植被覆盖人为影响的时空格局   总被引：3，自引：0，他引：3  

王建邦  赵军  李传华  朱钰  康重阳  高超 《地理学报》2019,74(3):504-519

基于MODIS-NDVI和气温、降水数据,使用基于变异系数的人为影响模型定量计算了2001-2015年中国植被覆盖人为影响,辅以趋势分析、Hurst指数等方法探讨了中国植被覆盖人为影响的时空变化特征及未来演变趋势。研究发现：① 2001-2015年,中国植被覆盖人为影响由南向北空间分异愈发明显,年均值为-0.0102,植被覆盖在人类活动影响下轻微减少,负影响面积占51.59%,略大于正影响面积。② 中国植被覆盖人为影响年际变化特征明显,整体呈负影响波动减少趋势,降速为0.5%/10a,其中正影响、负影响均呈增大趋势,正影响增速（0.3%/10a）远大于负影响（0.02%/10a）。③ 2001-2015年间,中国植被覆盖人为正影响重心向东北方向移动,负影响重心向西南方向移动,东北部植被覆盖在人为影响下不断改善,西南部人类活动对植被破坏程度不断增大。④ 中国植被覆盖人为影响主要呈负影响减少和正影响增大趋势,面积占比分别为28.14%和25.21%,生态环境趋于改善。⑤ Hurst指数分析表明,中国植被覆盖人为影响未来演变趋势的反向特征强于正向特征,主要呈人为负影响先减少后增大趋势,面积占比15.59%。  相似文献   

基于Stacking集成学习的恒星/星系分类研究          下载免费PDF全文

李超  张文辉  李然  王俊义  林基明 《天文学报》2020,61(2):21-111

机器学习在当今诸多领域已经取得了巨大的成功,但是机器学习的预测效果往往依赖于具体问题.集成学习通过综合多个基分类器来预测结果,因此,其适应各种场景的能力较强,分类准确率较高.基于斯隆数字巡天(Sloan Digital Sky Survey,SDSS)计划恒星/星系中最暗源星等集分类正确率低的问题,提出一种基于Stacking集成学习的恒星/星系分类算法.从SDSS-DR7(SDSS Data Release 7)中获取完整的测光数据集,并根据星等值划分为亮源星等集、暗源星等集和最暗源星等集.仅针对分类较为复杂且困难的最暗源星等集展开分类研究.首先,对最暗源星等集使用10折嵌套交叉验证,然后使用支持向量机(Support Vector Machine,SVM)、随机森林(Random Forest,RF)、XGBoost(eXtreme Gradient Boosting)等算法建立基分类器模型;使用梯度提升树(Gradient Boosting Decision Tree,GBDT)作为元分类器模型.最后,使用基于星系的分类正确率等指标,与功能树(Function Tree,FT)、SVM、RF、GBDT、XGBoost、堆叠降噪自编码(Stacked Denoising AutoEncoders,SDAE)、深度置信网络(Deep Belief Network,DBN)、深度感知决策树(Deep Perception Decision Tree,DPDT)等模型进行分类结果对比分析.实验结果表明,Stacking集成学习模型在最暗源星等集分类中要比FT算法的星系分类正确率提高了将近10%.同其他传统的机器学习算法、较强的提升算法、深度学习算法相比,Stacking集成学习模型也有较大的提升.  相似文献   

日本“3·11”海啸引起的乐清湾共振研究          下载免费PDF全文

刘勇  卢文芳  应超  李新文  姚文伟 《海洋学研究》2019,37(3):31-39

本文基于TELEMAC-2D模型建立太平洋区域海啸传播模型,模拟2011年日本“3·11”海啸事件下海啸波的传播。使用实测数据对该模型进行验证,在模型验证良好的基础上分析日本“3·11”海啸事件对乐清湾的影响。通过频谱分析得到“3·11”海啸激发的乐清湾内240、180和103 min这3个主导模态的幅值及其相位。通过白噪声实验对乐清湾的固有共振特征进行估算,进一步支持了乐清湾在上述3个模态发生共振这一结论。白噪声实验还表明,海啸等海洋灾害发生时会在乐清湾湾顶及湾口处产生较大的增水,该结论对乐清湾内海洋灾害风险防范具有指导意义。  相似文献   

Earth's rotation variations: a wavelet analysis     

Benjamin F. Chao  WeiYung Chung  ZongRong Shih  YiKai Hsieh 《地学学报》2014,26(4):260-264

Historical to up‐to‐date data of the minute variations in the solid Earth's rotation are subjected to a comprehensive time‐frequency wavelet analysis. The length‐of‐day for the period 1962–2012 confirms the presence of a prominent, robust 6‐year periodicity and reveals an anomalously strong 18.6‐year tidal oscillation as well as a ~13‐year quasi‐periodic signal. The polar‐motion excitation for the period 1900–2012 validates the existence of the ~26‐year Markowitz wobble and shows an ~8‐year quasi‐periodic signal, but no appreciable 18.6‐year periodicity. Although it is known that exchanges of angular momentum with the geophysical fluids are responsible for the rotational variations of the solid Earth, the exact physical mechanisms involved on interannual‐to‐decadal timescales are still far from understood.  相似文献   

Analysis of Jiangsu Tidal Flats Reclamation from 1974 to 2012 Using Remote Sensing     

赵赛帅  刘永学  李满春  孙超  周旻曦  张荷霞 《中国海洋工程》2015,(1):143-154

Jiangsu has the most abundant tidal flat resources among China's coastal provinces.To ease the conflict between the growing population and shrinking usable land and to promote regional sustainable development,large-scale coastal reclamation development activities have been performed in Jiangsu Province since 1949.The present study has integrated multi-source remote sensing images during 1974 to 2012 by using a Multi-point Fast Marching Method(MFMM) to extract the Jiangsu coastal reclamation areas for different time periods.The temporal and spatial patterns of the extent and elevation of the reclamation areas were analysed in order to determine the unused potential for future reclamation.It will provide information necessary to support the development and construction of tidal flats in Jiangsu.Results show that:(1) the reclaimed tidal flats along the Jiangsu coast cover more than 19.86×104 hm2,of which 13.97×104 hm2 is located in Yancheng,4.84×104 hm2 in Nantong,and 1.05×104 hm2 in Lianyungang;(2) the average elevation of the reclaimed Jiangsu tidal flats has gradually decreased over the last 40 years,while those in Dongtai and Rudong have showed particularly accelerated decrease since the 1990s;and(3) in 2012,very few unused tidal flats two meters above the sea level are left along the Jiangsu coast,and mainly concentrated in Yancheng.As there are still reserving some coastal land resources between 0-2 m,providing us with a potential for future development.All of these findings may be useful for researchers and local authorities for the development and utilization of tidal flat resources in Jiangsu.  相似文献   

Rift structures and its related unconformities on and adjacent the Dongsha Rise: insights into the nature of the high-velocity layer in the northern South China Sea     

Lei  Chao  Ren  Jianye  Pang  Xiong 《Marine Geophysical Researches》2019,40(2):99-110

Marine Geophysical Research - It is curious that the typical feature of high-velocity layer (HVL) underneath the crust for the magma-rich margin was found in the magma-poor margin of the South...  相似文献   

BDS卫星失效对区域定位精度的影响评估     

徐炜  徐梅  严超  王涛 《大地测量与地球动力学》2018,38(11):1133-1136

基于STK软件实现了2016-09 BDS系统星座结构的仿真，并选取可见卫星数、DOP值、系统可用性作为评估BDS卫星星座设计结构的指标，分析单颗与全部倾斜轨道卫星（IGSO）、地球静止轨道卫星（GEO）失效后对我国大陆地区BDS系统可用性的影响。结果表明，IGSO4卫星与GEO5卫星失效后对BDS在区域的定位性能影响较大，失效后的GDOP值分别为1.98、2.16。取BDS卫星正常运行时区域平均GDOP最大值(S=2.60)作为系统可用性阈值时，系统可用性分别降低了1.79%、32.63%；阈值取2S(5.20)、3S(7.80)、4S(10.40)、5S(13.00)时，系统可用性均可达100.00%。GEO整体失效后BDS系统在高精度定位中仍部分可用，而IGSO整体失效后BDS系统可用性受到大幅度限制。因此，增加在轨备份卫星时需重点考虑GEO5、IGSO4，并适当增加IGSO卫星的数目。  相似文献