A new method to compare hourly rainfall between station observations and satellite products over central-eastern China     

陈昊明  宇如聪  沈艳 《Acta Meteorologica Sinica》2016,30(5):737-757

This study employs a newly defined regional-rainfall-event (RRE) concept to compare the hourly characteristics of warm-season (May-September) rainfall among rain gauge observations, China merged hourly precipitation analysis (CMPA-Hourly), and two commonly used satellite products (TRMM 3B42 and CMORPH). By considering the rainfall characteristics in a given limited area rather than a single point or grid, this method largely eliminates the differences in rainfall characteristics among different observations or measurements over central-eastern China. The results show that the spatial distribution and diurnal variation of RRE frequency and intensity are quite consistent among different datasets, and the performance of CMPA-Hourly is better than the satellite products when compared with station observations. A regional rainfall coefficient (RRC), which can be used to classify local rain and regional rain, is employed to represent the spatial spread of rainfall in the limited region defining the RRE. It is found that rainfall spread in the selected grid box is more uniform during the nocturnal to morning hours over central-eastern China. The RRC tends to reach its diurnal maximum several hours after the RRE intensity peaks, implying an intermediate transition stage from convective to stratiform rainfall. In the afternoon, the RRC reaches its minimum, implying the dominance of local convections on small spatial scale in those hours, which could cause large differences in rain gauge and satellite observations. Since the RRE method reflects the overall features of rainfall in a limited region rather than at a fixed point or in a single grid, the widely recognized overestimation of afternoon rainfall in satellite products is not obvious, and thus the satellite estimates are more reliable in representing sub-daily variation of rainfall from the RRE perspective. This study proposes a reasonable method to compare satellite products with rain gauge observations on the sub-daily scale, which also has great potential to be used in evaluating the spatiotemporal variation of cloud and rainfall in numerical models.  相似文献   

Momentum budget diagnosis and the parameterization of subgrid-scale orographic drag in global GRAPES   总被引：2，自引：0，他引：2  

陈起英  沈学顺  孙健  刘琨 《Acta Meteorologica Sinica》2016,30(5):771-788

The initial tendency approach is used to diagnose systematic errors in global GRAPES (Global/Regional Assimilation Prediction System), including overly strong westerlies in the northern midlatitudes, cold/warm bias dipoles in the vicinity of the tropopause, and excessively strong southerlies in downstream regions of the Tibetan Plateau. This approach, involving the use of the assimilation system, focuses on the first few time steps of numerical weather forecasts to identify the deficiencies in diabatic forcing. The results show that there is insufficient diabatic dissipation in the upper troposphere and lower stratosphere of the northern midlatitudes and the lower troposphere of most latitudes, which results from the absence of a parameterization of subgrid orographic drag in global GRAPES. A scheme to parameterize the effects of these drags is therefore tested and the experiments indicate that the newly introduced scheme reduces zonal momentum budget residuals, weakens the northern midlatitude westerlies and southerlies in the downstream regions of the Tibetan Plateau, decreases the cold/warm bias dipoles, and leads to improved objective verification scores.  相似文献   

质量守恒的订正算法在GRAPES_GFS中的应用   总被引：1，自引：0，他引：1       下载免费PDF全文

苏勇  沈学顺  张倩 《应用气象学报》2016,27(6):666-675

如何在长时间积分的过程中保证模式大气的质量守恒是数值模式动力框架面临的基本问题之一,对于半拉格朗日动力框架来说, 在理论上要满足质量守恒面临着诸多的困难,质量订正方案不失为一种简单可行的选择。中国气象局数值预报中心的GRAPES_GFS (Global-Regional Assimilation and PrEdiction System, Global Forecast System) 在长时间积分过程中质量损失问题较为明显,该研究工作借鉴C-CAM (Climate-Community Atmosphere Model) 中对地面气压进行订正控制模式质量守恒的思路,在GRAPES_GFS中开发了一种对每个网格内的质量按照不同权重系数进行调整、控制模式大气总质量守恒的算法。经过一系列的试验,验证了该方法在GRAPES_GFS中的可行性,在保证模式质量守恒的情况下可有效减小高度场的预报偏差,缓解模式预报结果中天气系统偏弱的问题,在实际业务预报中有一定应用价值。  相似文献   

Modelling the spatial evolution of map objects by map agents     

Shen Ying  Wan Wen  Yuan Wan  Xinqiao Duan 《国际地球制图》2016,31(4):408-427

To overcome the weakness of modelling the relationships between map objects that represent the same geographic entities or phenomena at different times and scales, an agent-based approach is presented to modelling of the spatial evolution of map objects for better understanding of the evolutional process of different maps. Map agents are used to establish and manage the many-to-many corresponding relationships between map objects, and they render map objects active rather than traditionally passive. The evolutions of map objects are modelled by map agents using association and generation relationships to model the connectivity between map objects. This effort reduces the workload of multi-scale map updating by avoiding update of the entire map; instead, it simply allows map agents to detect, perceive and choose suitable behaviours on which to operate and update a spatially evolving object. Experiments of specific examples are presented to demonstrate the feasibility and the effectiveness of our approach.  相似文献   

Evolution of the groundwater system under the impacts of human activities in middle reaches of Heihe River Basin (Northwest China) from 1985 to 2013   总被引：1，自引：0，他引：1  

Lina Mi  Honglang Xiao  Jianming Zhang  Zhenliang Yin  Yongping Shen 《Hydrogeology Journal》2016,24(4):971-986

Investigation of the evolution of the groundwater system and its mechanisms is critical to the sustainable management of water in river basins. Temporal and spatial distributions and characteristics of groundwater have undergone a tremendous change with the intensity of human activities in the middle reaches of the Heihe River Basin (HRB), the second largest arid inland river basin in northwestern China. Based on groundwater observation data, hydrogeological data, meteorological data and irrigation statistical data, combined with geostatistical analyses and groundwater storage estimation, the basin-scaled evolution of the groundwater levels and storage (from 1985 to 2013) were investigated. The results showed that the unbalanced allocation of water sources and expanded cropland by policy-based human activities resulted in the over-abstraction of groundwater, which induced a general decrease in the water table and groundwater storage. The groundwater level has generally fallen from 4.92 to 11.49 m from 1985 to 2013, especially in the upper and middle parts of the alluvial fan (zone I), and reached a maximum depth of 17.41 m. The total groundwater storage decreased by 177.52?×?10⁸ m³; zone I accounted for about 94.7 % of the total decrease. The groundwater balance was disrupted and the groundwater system was in a severe negative balance; it was noted that the groundwater/surface-water interaction was also deeply affected. It is essential to develop a rational plan for integration and management of surface water and groundwater resources in the HRB.  相似文献   

Population geography in China since the 1980s: Forging the links between population studies and human geography     

Yu Zhu  Jinhong Ding  Guixin Wang  Jianfa Shen  Liyue Lin  Wenqian Ke 《地理学报(英文版)》2016,26(8):1133-1158

This paper reviews the progress of population geography in China since the 1980s. The review results suggest that contrary to the common perception of its invisibility and marginalized status in the field, tremendous progress has been made in population geography in China since the 1980s. Population geographers have made significant contribution to the understanding of a wide range of population issues from geographical perspectives, including migration, urbanization, population distribution, the relationships between population, environment and resources, aging, marriage patterns, and migrants’ crimes, although such contribution often did not appear in the geographical circle. Furthermore, population geographers have played an indispensable role in revitalizing population studies in China and forging its links to human geography, occupying an important position in this multi-disciplinary field. Population geographers’ contribution to the areas of migration and urbanization research has been particularly significant, reflected in their leading roles in these areas’ research. The paper demonstrates that as latecomers in the field after more than 20 years of isolation, population geographers in China have gone through a process of catching up and increasing engagement with developments in social sciences and increasing interaction with social scientists since the 1980s, and have benefited greatly from it; however, there is a tendency for population geography to be increasingly alienated from the main stream human geography, a phenomenon similar to but not exactly the same as Anglo-American geography in the late 1990s and early 2000s. The paper argues that population geography is only half way in the course to forge the links between population studies and human geography, and it needs to return to geographical sciences to strike a healthy balance between the field of population studies and that of human geography, and promote its further development in a multi-disciplinary field.  相似文献   

Relative contributions of boundary-layer meteorological factors to the explosive growth of PM<Subscript>2.5</Subscript> during the red-alert heavy pollution episodes in Beijing in December 2016     

Junting Zhong  Xiaoye Zhang  Yaqiang Wang  Junying Sun  Yangmei Zhang  Jizhi Wang  Kaiyan Tan  Xiaojing Shen  Haochi Che  Lu Zhang  Zhouxiang Zhang  Xuefei Qi  Huarong Zhao  Sanxue Ren  Yang Li 《Acta Meteorologica Sinica》2017,31(5):809-819

Based on observations of urban mass concentration of fine particulate matter smaller than 2.5 μm in diameter (PM_2.5), ground meteorological data, vertical measurements of winds, temperature, and relative humidity (RH), and ECMWF reanalysis data, the major changes in the vertical structures of meteorological factors in the boundary layer (BL) during the heavy aerosol pollution episodes (HPEs) that occurred in winter 2016 in the urban Beijing area were analyzed. The HPEs are divided into two stages: the transport of pollutants under prevailing southerly winds, known as the transport stage (TS), and the PM_2.5 explosive growth and pollution accumulation period characterized by a temperature inversion with low winds and high RH in the lower BL, known as the cumulative stage (CS). During the TS, a surface high lies south of Beijing, and pollutants are transported northwards. During the CS, a stable BL forms and is characterized by weak winds, temperature inversion, and moisture accumulation. Stable atmospheric stratification featured with light/calm winds and accumulated moisture (RH > 80%) below 250 m at the beginning of the CS is closely associated with the inversion, which is strengthened by the considerable decrease in near-surface air temperature due to the interaction between aerosols and radiation after the aerosol pollution occurs. A significant increase in the PLAM (Parameter Linking Aerosol Pollution and Meteorological Elements) index is found, which is linearly related to PM mass change. During the first 10 h of the CS, the more stable BL contributes approximately 84% of the explosive growth of PM_2.5 mass. Additional accumulated near-surface moisture caused by the ground temperature decrease, weak turbulent diffusion, low BL height, and inhibited vertical mixing of water vapor is conducive to the secondary aerosol formation through chemical reactions, including liquid phase and heterogeneous reactions, which further increases the PM_2.5 concentration levels. The contribution of these reaction mechanisms to the explosive growth of PM_2.5 mass during the early CS and subsequent pollution accumulation requires further investigation.  相似文献   

激光雷达与微波辐射计联合观测大气边界层高度变化     

沈建  沈利洪  韩笑  孙新会  李展  盛世杰  伍德侠  张天舒 《气象科技》2017,45(3):425-429

为了研究苏州地区大气边界层结构的日变化及季节特征,利用2014年1—7月期间大气颗粒物激光雷达对苏州上空大气气溶胶进行了连续观测。选定2014年1月15日、3月16日、5月7日与7月22日全天的消光系数探测数据,通过优化后的梯度法得到了该地区的大气边界层高度,分析了其日变化特征,并分析了边界层高度与地表的温湿变化之间的相关性。结果表明除1月15日外,边界层的变化与地表温度存在明显的正相关,而与地表的相对湿度存在负相关。同时,对站点微波辐射计观测得到的温湿廓线与边界层内消光系数廓线进行了联合研究。研究结果表明,微波辐射计湿度垂直廓线与激光雷达消光系数廓线探测得到的边界层具有良好的一致性。  相似文献   

1951—2013年我国冬季气温年代际变化与PDO的关系     

徐忆菲  彭丽霞  李季  申双和 《气象科技》2017,45(4):669-677

利用我国160个测站1951—2013年冬季月平均气温资料和1951—2016年间冬季太平洋年代际振荡(PDO：Pacific Decadal Oscillation)指数资料,分析了两者在年际和年代际时间尺度上的相关关系,探讨了PDO对我国冬季气温影响的可能物理过程。结果发现：PDO与我国冬季气温年际变化不显著;在冬季期间,PDO对我国气温的影响是滞后的;PDO与我国冬季气温年代际变化存在密切关系,当PDO处于年代际正(负)位相时,我国气温普遍偏高(低);PDO年代际分量对我国的影响机制为：当PDO指数位于年代际正(负)位相时段,海平面气压场上西伯利亚高压减弱(增强),500 hPa高度场东亚大槽强度减弱(增强),200 hPa纬向风场东亚北支急流减弱(增强),这些都有利于我国冬季气温偏高(低)。  相似文献   

An improved GRACE monthly gravity field solution by modeling the non-conservative acceleration and attitude observation errors     

Qiujie Chen  Yunzhong Shen  Wu Chen  Xingfu Zhang  Houze Hsu 《Journal of Geodesy》2016,90(6):503-523

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