基于精确Riemann求解器的明满流过渡过程模拟          下载免费PDF全文

孙万光  李成振  马军  范宝山 《水科学进展》2021,31(6):936-945

Preissmann窄缝法模拟明满流过渡过程方法简单,但存在明显的非物理振荡,抑制非物理振荡是该方法应用的关键。基于Godunov格式和精确Riemann求解器对明满流过渡过程进行模拟,针对Riemann问题代数恒等式在明满流交界处不光滑问题,提出了三阶收敛方法与二分法结合的迭代求解方法,保证迭代收敛至真实解;针对由于变量空间重构方法不能准确表达变量在空间中真实物理状态而导致的非物理振荡,提出了基于精确Riemann解的变量空间重构方法,准确表达激波间断在单元内的空间分布状态,从机理上抑制了非物理振荡。实例研究表明,数值计算结果与解析解或实测值吻合良好,研究成果为明满流过渡过程的高精度数值模拟提供了新的方法。  相似文献   

云南石林喀斯特露石径流输出及其影响因素探究   总被引：1，自引：0，他引：1  

王庆贺  赵志猛  沈有信 《地球学报》2021,42(3):383-390

喀斯特露石具有重要的生态功能,但关于露石承接降水后的石面径流及其影响因子研究仍然很少.本实验选择云南石林的石漠化、人工林、原生林生态系统,布设露石径流收集装置,收集并测量不同降雨事件后的露石石面径流,测定露石承接降水面积和粗糙度.结果表明:(1)在3.92 mm到72.31 mm的降雨范围内,露石承接降雨量与露石径流量间存在极显著的正相关关系.(2)降雨量,林冠覆盖,露石粗糙度均影响露石径流输出.降雨量与露石径流深成显著正相关关系;石漠化生态系统的露石承接降雨量和露石径流输出显著高于两类林地;露石径流输出随露石粗糙度的增加而减小,两者间存在显著的负相关关系.(3)石漠化生态系统的降雨-露石径流转换系数为0.483,显著高于人工林生态系统的0.434和原生林生态系统的0.413,但两类林地的差异性仅在降雨量为小雨时显著.多因素影响下的喀斯特露石径流具有高度异质性,其将对土壤水分、养分异质性与生物多样性的形成产生重要影响.  相似文献   

中国月尘探测进展及后续展望     

李存惠  张小平  张熇  王鹢  谢良海  严奇  马继楠  张海燕  庄建宏  赵呈选 《吉林大学学报(地球科学版)》2021,51(4):1276-1283

月球尘埃研究具有重要的科学和工程价值。目前对月球尘埃运动规律、运动机理等的了解非常有限,对尘埃运动物理参数缺少系统的定量测量,严重制约了月球尘埃的科学研究。阿波罗17号宇航员观察到的月尘扬起及其物理机制迄今为止在科学上仍然是一个谜。中国的嫦娥三号月球探测任务得到了月面上的尘埃沉积数据及尘埃活动高度数据,表明尘埃活动具有显著的地域差异。在嫦娥五号采样返回任务中将研究月尘带电方面的物理特性。探月后续任务中如果能够在高纬度地区首次系统地定量测量月尘运动的物理参数,将会揭示不同经纬度区域、不同太阳光照条件、不同太阳风条件、不同地形条件下的尘埃活动规律及其关键影响因素,对高精度数值模型的建立及其参数选择提供定量限制,必将取得新的重要科学发现。  相似文献   

GFS模式地形高度偏差对地面2m气温预报的影响          下载免费PDF全文

智协飞  吴佩  俞剑蔚  慕建利  赵倩 《大气科学学报》2019,42(5):652-659

利用2016年1月1日—12月31日全球预报系统(GFS,Global Forecasting System)1～5 d的2 m气温预报资料,以及同期中国地面气象站2 m气温观测资料,研究模式地形高度偏差对地面2 m气温预报的影响。结果表明,较大模式地形高度偏差可严重影响2 m气温模式预报性能,导致较大预报误差。随着模式预报时效延长,2 m气温预报均方根误差也略有增加。比较模式地形高度偏差和预报时效对于模式预报性能的影响,发现模式地形高度偏差对于模式预报效果的影响更加显著。两种地形订正方案,即不做温度垂直订正的线性回归以及对温度进行垂直订正的线性回归都能显著减小2 m气温模式预报的误差,后者的订正效果更好。  相似文献   

GRAPES全球集合预报初始条件及模式物理过程不确定性方法研究   总被引：3，自引：0，他引：3       下载免费PDF全文

李晓莉  陈静  刘永柱  彭飞  霍振华 《大气科学学报》2019,42(3):348-359

为描述GRAPES全球模式初始条件的不确定性,基于适合集合预报应用的GRAPES全球奇异向量技术,依据大气初始误差符合正态分布的特征,采用高斯取样奇异向量来构造全球集合预报初始扰动,在此基础上建立了GRAPES全球集合预报系统(GRAPES-GEPS)。利用GRAPES全球同化分析场,对采用初始扰动的GRAPES-GEPS连续试验预报结果进行检验和分析。结果表明:GRAPES-GEPS中高度场、风场及温度场预报的集合离散度能有效快速增加,集合平均均方根误差与集合离散度的关系合理;相对控制预报的均方根误差,集合平均的预报优势在预报中期非常显著。为进一步体现GRAPES-GEPS中模式物理过程的不确定性,发展了模式物理过程倾向随机扰动技术(SPPT)。试验结果表明:SPPT方案的应用有效提高了GRAPES-GEPS在南、北半球和热带地区等压面要素预报的集合离散度,同时一定程度减小了集合平均误差,进而改进了集合平均误差与集合离散度的关系,其中SPPT方案在热带地区的改进最为显著。本文发展的基于奇异向量的初始扰动方法和模式扰动SPPT方案在中国气象局2018年12月业务化运行的GRAPES-GEPS中得到了应用。  相似文献   

新时代城市地质工作战略思考   总被引：2，自引：0，他引：2  

程光华  杨洋  赵牧华  苏晶文  李云峰 《地质论评》2018,64(6):1438-1446

中国共产党“十九大”提出了满足人民美好生活、人与自然和谐共生的目标,而现有城市地质工作体系不论从理论技术还是理念上,都难以满足服务“绿色、低碳、循环、安全、集约、智慧”城市发展需求,需要建立适应城市发展要求的新时代城市地质工作体系。我国现有城市地质工作经历了2003年以前单要素调查、2003以来多专业综合地质调查两个阶段,虽然在一定程度上服务了城市建设,但尚不能满足新时代城市国土空间立体可持续开发的需要。本文在全面分析国内外城市地质工作现状和存在问题的基础上,对新时代城市地质工作进行战略思考,提出建立以地球系统理论为指导,以多场扰动再平衡、全空间资源与环境评价以及空间资源协同规划等理论为基础的城市地质学理论体系;建立包括1项调查、3项评价、1套监测系统、1套信息系统的“1311”城市地质工作体系;提出新时代城市地质工作新机制。  相似文献   

Study on Jinan urban construction planning based on the protection of karst landscape          下载免费PDF全文

SUN Bin  YU Da-lu 《地下水科学与工程》2018,6(4):280-292

Study on urban construction planning based on karst landscape protection contributes to sustainable development of urban construction in karst area. Jinan is a city famous for karst spring water. Karst landscape plays a decisive role in urban construction. Through hydrogeological analysis, the distribution characteristics of karst mountain, cave, gully and flat dam in Jinan are analyzed. It is revealed that various karst landforms are involved in the spring circulation process to varying degrees. Some karst landforms have been destroyed in the process of urban construction and the karst landscape has been overexploited resulting in the direct or indirect weakening of spring water recharge and infiltration capacity and the decrease of spring water flow. Through the study of the principle of organic combination of karst landscape and urban construction planning, on the basis of protecting the ecological environment of the south, paying attention to the overall protection of the karst geomorphology system and the principle of accessibility of the karst landscape, the development countermeasures guided by urban planning are put forward based on karst landforms protection. On the basis of fully considering the special karst landform conditions in Jinan, the countermeasures are that the ecological control red line of urban construction planning should be set up based on karst mountains and valleys in southern of Jinan City. It is suggested that the bare carbonate rock continuous mountain foot line in the direct recharge area should be taken as the south control red line of urban development and included in the overall planning. The urban landscape is mainly displayed in the main axis based on karst mountains and springs, constructing East-West Axis-characteristic Landscape Belt along the Wufeng Mountain-Langmao Mountain-Hero Mountain-Qianfo Mountain-Long cave-Panlong cave-Jinping Mountain line and North-South Axis Landscape Belt along the Baotu Spring- Qianfo Mountain line, Baiquan-Panlong cave line, Baimai spring-Dajian Mountain line. Based on the karst river valleys and the river system, the urban spatial pattern is constructed, forming ecological corridor, restoring infiltration function of river. The form of urban construction should be shaped based on karst landform and the river system. The main form is semi-star like radiation type and the combination of central intensive type and zonal type. Based on the whole protection of karst geomorphology system and the scientific molding of karst landscape, the ecological landscape city with the symbiosis of spring and urban can be built.  相似文献   

Estimation of forest aboveground biomass from HJ1B imagery using a canopy reflectance model and a forest growth model     

Xinyun Wang  Yige Guo  Jie He  Lingtong Du  Tianhua Hu 《国际地球制图》2018,33(2):148-162

Accurately estimating the spatial distribution of forest aboveground biomass (AGB) is important because of its carbon budget forms part of the global carbon cycle. This paper presented three methods for obtaining forest AGB based on a forest growth model, a Multiple-Forward-Mode (MFM) method and a stochastic gradient boosting (SGB) model. A Li-Strahler geometric-optical canopy reflectance model (GOMS) with the ZELIG forest growth model was run using HJ1B imagery to derive forest AGB. GOMS-ZELIG simulated data were used to train the SGB model and AGB estimation. The GOMS-ZELIG AGB estimation was evaluated for 24 field-measured data and compared against the GOMS-SGB model and GOMS-MFM biomass predictions from multispectral HJ1B data. The results show that the estimation accuracy of the GOMS-MFM model is slightly higher than that of the GOMS-SGB model. The GOMS-ZELIG and GOMS-MFM models are considerably more accurate at estimating forest AGB in arid and semiarid regions.  相似文献   

Vegetation change and fragmentation in the mega city of Delhi: Mapping 25 years of change     

《Applied geography (Sevenoaks, England)》2015

Delhi, the worlds' second most populous city, has experienced rapid, planned and unplanned expansion at the cost of its green cover in recent decades. In this study, we use satellite images from 1986, 1999 and 2010 to map changes in urban and green cover, assess the fragmentation of green spaces, and identify the drivers of change. We find that urban patterns of development have shaped the distribution and fragmentation of green spaces, with the city center containing more green spaces with less fragmentation compared to intermediate areas and the peri-urban periphery. Yet, the city core has also experienced the greatest degree of vegetation clearing and fragmentation over time due to infrastructural expansion, while the peri-urban periphery has shown an increase in vegetation and a decrease in fragmentation due to recent compensatory plantation in these peripheral areas. Forests, archaeological sites, and military and academic campuses have played a major role in protecting green cover and limiting fragmentation in the core and intermediate areas of the city. This research helps in advancing our understanding of the pattern–process relationship between urbanization and land cover change/fragmentation in India's largest city.  相似文献   

The role of NGOs in public and private land development: The case of Dhaka city     

《Geoforum》2015

Through a series of case studies, this paper discusses the three stakeholders in land development for housing in Dhaka city: the public and private sectors, and NGOs. In a scenario in which urban planning merely serves to the fulfil formal requirements and benefit certain groups, in which the public sector is an accomplice to the private sector, and where NGOs have their own private interests; urban planning in the public interest is interlocked with private interests. NGOs are important tertiary stakeholders in planning and service provision. While they vary in their types and objectives, environment NGOs in particular often find themselves in an antagonistic position concerning public and private land development. However, the interventions to the public and private sectors placed by the NGOs can provide a platform for future negotiation and participation in policy formulation.  相似文献