A fine-granularity scheduling algorithm for parallel XDraw viewshed analysis     

Wanfeng Dou  Yanan Li  Yanli Wang 《Earth Science Informatics》2018,11(3):433-447

Viewshed analysis is widely used in many terrain applications such as siting problem, path planning problem, and etc. But viewshed computation is very time-consuming, in particular for applications with large-scale terrain data. Parallel computing as a mainstream technique with the tremendous potential has been introduced to enhance the computation performance of viewshed analysis. This paper presents a revised parallel viewshed computation approach based on the existing serial XDraw algorithm in a distributed parallel computing environment. A layered data-dependent model for processing data dependency in the XDraw algorithm is built to explore scheduling strategy so that a fine-granularity scheduling strategy on the process-level and thread-level parallel computing model can be accepted to improve the efficiency of the viewshed computation. And a parallel computing algorithm, XDraw-L, is designed and implemented taken into account this scheduling strategy. The experimental results demonstrate a distinct improvement of computation performance of the XDraw-L algorithm in this paper compared with the coarse-partition algorithm, like XDraw-E which is presented by Song et al. (Earth Sci Inf 10(5):511–523, 2016), and XDraw-B that is the basic algorithm of serial XDraw. Our fine-granularity scheduling algorithm can greatly improve the scheduling performance of the grid cells between the layers within a triangle region.  相似文献   

Real-time identification of urban rainstorm waterlogging disasters based on Weibo big data     

Yang Xiao  Beiqun Li  Zaiwu Gong 《Natural Hazards》2018,94(2):833-842

With the acceleration of urbanisation in China, preventing and reducing the economic losses and casualties caused by urban rainstorm waterlogging disasters have become a critical and difficult issue that the government is concerned about. As urban storms are sudden, clustered, continuous, and cause huge economic losses, it is difficult to conduct emergency management. Developing a more scientific method for real-time disaster identification will help prevent losses over time. Examining social media big data is a feasible method for obtaining on-site disaster data and carrying out disaster risk assessments. This paper presents a real-time identification method for urban-storm disasters using Weibo data. Taking the June 2016 heavy rainstorm in Nanjing as an example, the obtained Weibo data are divided into eight parts for the training data set and two parts for the testing data set. It then performs text pre-processing using the Jieba segmentation module for word segmentation. Then, the term frequency–inverse document frequency method is used to calculate the feature items weights and extract the features. Hashing algorithms are introduced for processing high-dimensional sparse vector matrices. Finally, the naive Bayes, support vector machine, and random forest text classification algorithms are used to train the model, and a test set sample is introduced for testing the model to select the optimal classification algorithm. The experiments showed that the naive Bayes algorithm had the highest macro-average accuracy.  相似文献   

积雪升华过程对高寒湿地陆气相互作用的影响     

张海宏  苏永玲  姜海梅  晁红艳  苏文将 《冰川冻土》2018,40(6):1223-1230

利用青海玉树隆宝地区2014年12月积雪升华过程的观测资料,分析了积雪升华过程中高寒湿地陆气相互作用特征及积雪深度对陆气相互作用的影响。结果表明：在降雪和积雪升华过程中,高寒湿地浅层土壤温度在短时期内有所升高,而深层土壤温度和土壤体积含水量对降雪过程的响应不敏感。积雪升华过程中净辐射、感热通量和潜热通量的日平均值增加,向上短波辐射的日平均值减少。积雪逐渐升华导致地表吸收的能量增加,同时地表向大气传递的能量也随之增加。随着积雪的逐步升华,感热占比和潜热占比逐渐升高,而土壤热通量占比和热储存占比逐渐降低。积雪深度增加会导致地表反照率和地表比辐射率增大,感热输送系数减小。  相似文献   

黑龙江省两次温带气旋暴雪过程对比分析     

周显伟  赵宇  祝玉梅  娄德君 《冰川冻土》2018,40(6):1195-1206

利用多种资料对黑龙江省两次由江淮气旋和蒙古气旋合并引发的暴雪过程的水汽、热动力条件和中尺度特征进行了对比分析。结果表明：（1）两次暴雪过程都发生在北支槽和短波槽合并、北支槽北部有冷涡的背景下,850 hPa上低涡合并促使江淮气旋和蒙古气旋合并;气旋合并后,低空急流为降雪提供了充足水汽,强暖平流使气旋爆发性发展,导致降雪加强。（2）两次降雪过程都表现出逗点云系的合并发展,"1211 "暴雪过程中高层形成涡旋偏西,700 hPa低涡东部偏南风引导气旋北上西折,低空急流和地形共同作用使暖湿空气强烈辐合上升,产生对流云,暴雪发生在A类逗点云系的头部,降雪强度大,范围广;"1412"暴雪过程高空槽低涡位置偏东,700 hPa低涡东部西南风始终引导气旋向东北方向移动,近地面层具有冷垫,暴雪主要发生在B类气旋逗点云系头部西侧中低云团中,降雪范围和强度较"1211"过程小。（3）低层（0.3 km）冷空气侵入和中高层（5.5 km）转为偏北风对判断降雪开始和结束有很好的表征意义。（4）冷涡前部强高压脊使冷涡移动缓慢,从而延长了降水的持续时间,气旋移动路径与高压脊伸展方向密切相关。  相似文献   

A comparative frequency analysis of three standardized drought indices in the Poyang Lake basin,China     

Guixia Yan  Zhiyong Wu  Denghua Li  Heng Xiao 《Natural Hazards》2018,91(1):353-374

Regional drought frequency analysis was carried out in the Poyang Lake basin (PLB) from 1960–2014 based on three standardized drought indices: the standardized precipitation index (SPI), the standardized precipitation evapotranspiration index (SPEI) and the standardized Palmer drought index (SPDI). Drought events and characteristics were extracted. A Gumbel–Hougaard (GH) copula was selected to construct the bivariate probability distribution of drought duration and severity, and the joint return periods (T _a ) were calculated. Results showed that there were 50 (50 and 40) drought events in the past 55 years based on the SPI (SPEI and SPDI), and 9 (8 and 10) of them were severe with T _a more than 10 years, occurred in the 1960s, the 1970s and the 2000s. Overall, the three drought indices could detect the onset of droughts and performed similarly with regard to drought identification. However, for the SPDI, moisture scarcity was less frequent, but it showed more severe droughts with substantially higher severity and longer duration droughts. The conditional return period (Ts|d) was calculated for the spring drought in 2011, and it was 66a and 54a, respectively, based on the SPI and SPDI, which was consistent with the record. Overall, the SPI, only considering the precipitation, can as effectively as the SPEI and SPDI identify the drought process over the PLB under the present changing climate. However, drought is affected by climate and land-cover changes; thus, it is necessary to integrate the results of drought frequency analysis based on different drought indices to improve the drought risk management.  相似文献   

A model for the representation of emergency cases     

Chao Zhang  Jiansong Wu  Chao Huang  Bo Jiang 《Natural Hazards》2018,90(1):337-348

The aim of this paper is to propose a location model of earthquake emergency service depot on the basis of hybrid multi-attribute decision-making method. The advantage of the proposed method is that practical mixed uncertainty of location decision information is considered, and the corresponding factors that affect the location of transfer stations are contained. To solve the location problem, a hybrid multi-attribute decision procedure without information transformation is developed. Besides, a novel weighting method and aggregation process is given. Finally, a numerical example is provided to show the feasibility and validity of the proposed method.  相似文献   

Intraseasonal oscillation of the rainfall variability over Rwanda and evaluation of its subseasonal forecasting skill          下载免费PDF全文

Xuan Zhou  Lin Chen  Janet Umuhoza  Yifeng Cheng  Lu Wang  Ran Wang 《大气和海洋科学快报》2021,14(6):60-65

非洲中东部地区的经济主要依靠自给农业支撑,该地区农业经济对降水的变化尤为敏感.本文以卢旺达为例,观测分析指出卢旺达的次季节降雨主要集中在10-25天;根据次季节尺度降水变率的单点相关方法,发现卢旺达的次季节降水变率和周围区域变化一致;进一步合成结果显示该地区次季节降水变率与异常西风有关,这可追溯到赤道地区西传的赤道Rossby波.最后,本文评估了当前动力模式ECMWF对 卢旺达地区(即非洲中东部)次季节降水变率的预报能力,发现EC模式在对该区域降水和相关风场指数的预报技巧都在18天左右,且预报技巧表现出一定的年际差异,这可能与热带太平洋的背景海温信号有关.该工作增进了当 前对非洲中东部地区的次季节降水变率和预测水平的认知,并且对该地区国家粮食安全和防灾减灾具有启示性意义.  相似文献   

Possible contribution of the PDO to the eastward retreat of the western pacific subtropical high: PDO对西太平洋副热带高压年代际东退的可能贡献          下载免费PDF全文

《大气和海洋科学快报》2021,14(1):100005

Previous studies have demonstrated that the western Pacific subtropical high (WPSH) has experienced an eastward retreat since the late 1970s. In this study, the authors propose that this eastward retreat of the WPSH can be partly attributed to atmospheric responses to the positive phase of the Pacific decadal oscillation (PDO), based on idealized SST forcing experiments using the Community Atmosphere Model, version 4. Associated with the positive phase of the PDO, convective heating from the Indian Peninsula to the western Pacific and over the eastern tropical Pacific has increased, which has subsequently forced a Gill-type response to modulate the WPSH. The resulting cyclonic gyre over the Asian continent and the western Pacific in the lower troposphere is favorable for the eastward retreat of the WPSH. Additionally, the resulting anticyclonic gyre in the upper troposphere is favorable for the strengthening and southward expansion of the East Asian westerly jet, which can modulate the jet-related secondary meridional–vertical circulation over the western Pacific and promote the eastward retreat of the WPSH.摘要以往的研究已证实, 西太平洋副热带高压 (副高) 在1970s后期减弱东退.基于大气模式 (CAM4) 的理想型海温强迫试验, 结果表明:副高的东退可能是大气对于正位相太平洋年代际振荡 (PDO) 的相应.伴随着PDO转变为正位相, 西太平洋至印度半岛以及热带东太平洋的对流加热增强, 大气表现为Gill型响应, 在亚洲大陆至西太平洋上空低层产生气旋性异常, 有利于副高东退.同时, 高层产生反气旋异常, 使得东亚西风急流加强和向南扩展, 进而调节西太平洋上空的次级环流, 进一步有利于副高东退.  相似文献   

Trigger mechanism of a snow burst event in Northeast China: 东北一次雪飑事件的触发机制研究          下载免费PDF全文

《大气和海洋科学快报》2021,14(2):100017

A snow burst event characterized by brief heavy snowfall affected Northeast China and caused serious social impact on 26 January 2017, with the snowband generally aligned with a northeast–southwest-oriented cold front. ECMWF reanalysis data were used to diagnose the possible trigger mechanism. Results showed there were two stages: (a) an initial stage far away from the Changbai Mountains, and (b) an enhancement stage under the influence of high terrain. During the initial stage, the coupling of low-level frontogenesis and a favorable convergence pattern caused strong upward motion, contributing to the release of instability. When the snowband approached the high terrain during the enhancement stage, the various instabilities were triggered by the low-level frontogenesis, terrain circulation, and strong wind shear associated with the low-level jet. Further, a modified Q-vector divergence including generalized potential temperature was calculated to diagnose the vertical motion. It showed that the frontogenesis terms contributed greatly to the negative Q-vector divergence along the moist isentropes, while the pseudo-vorticity terms played a role in the regions with strong wind shear associated with the low-level jet in the warm section, suggesting both were important in stimulating the ascending motion. The regions with negative Q-vector divergence had a close relationship with the vertical structure of convection, indicating the potential to track the development of the snowband in the next few hours.摘要2017年1月26日, 中国东北地区发生了一次短时强降雪过程.本文利用ECMWF再分析数据诊断该过程的可能触发机制.分析表明, 该过程可分两个阶段:初生阶段降雪远离高地形, 低层锋生和有利的辐散场配置激发上升运动释放不稳定;增强阶段雪带接近长白山, 低层锋生,地形环流以及与低空急流有关的风切变共同释放锋前不稳定.本文进一步计算了包含广义位温的修正Q矢量方程.结果表明, 锋生项对沿湿等熵线的负Q矢量散度贡献较大, 而拟涡度项在暖区强风切变区域中比较显著, 两项在激发上升运动中同等重要.  相似文献   

Comparisons in the global planetary boundary layer height obtained from COSMIC radio occultation,radiosonde, and reanalysis data 基于无线电掩星数据, 探空资料以及再分析资料估算大气边界层高度的比较          下载免费PDF全文

《大气和海洋科学快报》2021,14(2):100018

The global planetary boundary layer height (PBLH) estimated from 11 years (2007–17) of Integrated Global Radiosonde Archive (IGRA) data, Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) soundings, and European Center for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) data, are compared in this study. In general, the spatial distribution of global PBLH derived from ERA-Interim is consistent with the one from IGRA, both at 1200 UTC and 0000 UTC. High PBLH occurs at noon local time, because of strong radiation energy and convective activity. There are larger differences between the results of COSMIC and the other two datasets. PBLHs derived from COSMIC are much higher than those from radiosonde and reanalysis data. However, PBLHs derived from the three datasets all exhibit higher values in the low latitudes and lower ones in the high latitudes. The latitudinal difference between IGRA and COSMIC ranges from −1700 m to −500 m, while it ranges from −500 m to 250 m for IGRA and ERA-Interim. It is found that the differences among the three datasets are larger in winter and smaller in summer for most studied latitudes.摘要用11年的全球无线电掩星数据 (COSMIC) , 无线电探空数据 (IGRA) 以及欧洲中心再分析资料 (ERA-Interim) 对全球大气边界层高度 (PBLH) 进行估算比较. 结果表明: (1) 在1200 UTC和0000 UTC, 由ERA-Interim和IGRA数据估算得到的全球PBLH空间分布较为一致, 相关性较好, 在白天正午时候太阳辐射能力较强, 对流活动频繁, 估算得到的大气边界层高度较高. (2) 由COSMIC掩星数据估算得到的边界层高度比探空数据和再分析数据估算结果整体偏大. (3) COSMIC掩星数据, IGRA 探空数据以及 ERA-Interim 再分析资料估算结果都表明边界层高度在低纬度地区偏大, 高纬度地区偏小. (4) 分析不同数据估算边界层高度纬向季节性差异表明, IGRA探空数据和COSMIC数据间差异为-1700m至-500m, IGRA与ERA-Interim之间的差异为-500m至250m.此外, 对于大多数纬度而言, 三个数据集之间的差异在冬季较大, 在夏季较小.  相似文献