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On the Relationship between Local topography and Small Glacier Change under Climatic Warming on Mt. Bogda, Eastern Tian Shan, China

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Journal of Earth Science 2011年第4期22卷 515-527页

作者：李开明李慧林王林高闻宇 State Key Laboratory of Cryospheric Sciences/Tianshan Glaciological Station Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences College of Geography and Environment Science Northwest Normal University

Glacial features in the geological record provide essential clues about past behavior of climate. Of the numerous physical systems on earth, glaciers are one of most responsive to climate change, especially small glaciers, their direct marginal response taking only a few years or decades to be expressed. Accelerating recession of modern glaciers raises the issue of the climate＇s impact on water runoff. Data based on topographic maps and Advanced Spaceborne Thermal Emission and Radiometer （ASTER） imagery show the trends that are highly variable over time and within the region. An analysis of the local topographic settings of very small （〈0.5 km2） glaciers was conducted to investigate their influence on recent changes in these glaciers. Among 137 glaciers, 12 disappeared completely. The study reveals that glaciers situated in favorable locations had tiny relative area reduction, while those in less favorable settings generally had large area loss or even disappeared. It is suggested that most of the small glaciers studied have retreated as far as they are likely to under the climatic conditions of the late 20th century. Undoubtedly, the strong retreating of small glaciers exerts adverse effects on the hydro- logic cycle and local socioeconomic development.

关键词： glacier change climatic warming topography Mt. Bogda remote-sensing.

Reverse-Time Prestack Depth Migration of GPR Data from topography for Amplitude Reconstruction in Complex Environments

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Journal of Earth Science 2015年第6期26卷 791-798页

作者： John H.Bradford Center for Geophysical Investigation of the Shallow Subsurface Boise State University

With increased computational power, reverse-time prestack depth migration（RT-PSDM） has become a preferred imaging tool in seismic exploration, yet its use has remained relatively limited in ground-penetrating radar（GPR） applications. Complex topography alters the wavefield kinematics making for a challenging imaging problem. Model simulations show that topographic variation can substantially distort reflection amplitudes due to irregular wavefield spreading, attenuation anomalies due to irregular path lengths, and focusing and defocusing effects at the surface. The effects are magnified when the topographic variations are on the same order as the depth of investigation––a situation that is often encountered in GPR investigations. Here, I use a full wave-equation RT-PSDM algorithm to image GPR data in the presence of large topographic variability relative to the depth of investigation. The source and receiver wavefields are propagated directly from the topographic surface and this approach inherently corrects for irregular kinematics, spreading and attenuation. The results show that when GPR data are acquired in areas of extreme topography, RT-PSDM can accurately reconstruct reflector geometry as well as reflection amplitude.

关键词： reverse-time prestack depth migration ground-penetrating radar topography wavefield reflector geometry reflection amplitude.

Quantitative assessment of the influence of terrace and check dam construction on watershed topography

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Frontiers of Earth Science 2020年第2期14卷 360-375页

作者： Guowei PANG Qinke YANG Chunmei WANG Rui LI Lu ZHANG Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity College of Urban and Environmental ScienceNorthwest UniversityXi’an 701027China Key Laboratory of Ecological Hydrology and Disaster Prevention in Arid Regions State Forestry and Grassland AdministrationXi’an 710127China Institute of Soil and Water Conservation CAS&MWRYangling 712100China Key Laboratory of Degraded and Unused Land Consolidation Engineering MNRXi’an 710075China

Terrace and check dam construction has substantially changed land surface morphology,which in turn affects modern surface processes.Digital elevation models(DEMs)provide an effective way to quantitatively analyze surface morphology and processes.However,existing DEMs lack sufficient ability to express artificial terrain.Based on 1:10000 topographic maps of the Zhifanggou watershed,a series of artificial terrain DEMs for the study site were constructed by both field investigation and remote sensing images from 1938 to 2010.Digital terrain analysis was used to quantitatively assess the influence of terrace and check dam construction on the watershed terrain.The results showed that the artificial terrain DEM could capture the spatial distribution patterns of terraces and dam lands and improved the ability of DEM to express terrain.The construction of terraces and check dams clearly changed the surface elevation.The average elevation change of each terrace mainly ranged between–1.5 and 1.5 m,while the annual average deposition height of the dam lands was 9.16 cm.The average slope,slope length,and slope length and steepness factor of the watershed decreased with the effect of the artificial terrain on the surface,and their averages decreased by 0.65°,6.75 m,and 0.83,respectively,from 1938 to 2010.Although the construction of terraces reduced their surface slope to nearly 0°,the slope of terrace embankments rapidly increased,to more than 45°,which may lead to gravitational erosion and potential terrace damage.Terracing reduced the slope length in both the terrace distribution area and downslope of the terraces.Check dam deposition reduced the slope and slope length of the channel.This study contributes to a better understanding of the topographic change rules after terrace and check dam construction,and aids in elucidating the mechanisms of soil erosion process influenced by artificial topography.

关键词： check dam digital elevation model Loess Plateau terrace topography

Effects of the Convex topography on Railway Environmental Vibrations

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Computer Modeling in Engineering & Sciences 2019年第1期118卷 177-205页

作者： Huaxi Lu Zhicheng Gao Luyao Xu Bitao Wu Department of Civil Engineering East China Jiaotong UniversityNanchang330013China.

The railway environmental vibration caused by high-speed railways is harmful to the human health,the structural safety of adjacent buildings,and the normal use of precision instruments.At the same time,it occurs frequently.In this case,the railway environmental vibration has drawn much attention with the rapid development of highspeed railways.Studies in Earthquake Engineering show that a convex topography has a great impact on ground vibrations,however,there is no consideration about the convex topographic effect in the study of the railway environmental vibration when the convex topography is near the roadway.In this paper,the influence of a convex topography on the railway environmental vibration was investigated.Two-dimensional(2D)finite element models consist of subgrade-convex topography and subgrade-flat topography are established using the finite element method.The length and the height of the analysis model are taken as 200 m and 41.3 m,respectively.The external soil of the calculation model is simulated via the artificial boundary.By comparison with measured results,the 2D finite element models were verified to be effective.The convex topographic effect is studied by conducting parameter investigations,such as the bottom width,cross-sectional shape,height-width ratio and the foundation soil properties.Results show that the dimension and cross-section shape of the convex topography and the foundation soil properties have significant effect on the convex topographic effect.

关键词： Railway environmental vibration convex topography ground acceleration ground displacement frequency spectra.

Numerically quantifying the relative importance of topography and buoyancy in driving groundwater flow

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Science China Earth Sciences 2010年第1期53卷 64-71页

作者： YANG JianWen 1,2,FENG ZuoHai 1,LUO XianRong 1 & CHEN YuanRong 1 1 Faculty of Earth Sciences,Guilin University of Technology,Guilin 541004,China 2 Department of Earth and Environmental Sciences,University of Windsor,Windsor,Ontario,N9B 3P4,Canada Faculty of Earth Sciences Guilin University of Technology Guilin China Department of Earth and Environmental Sciences University of Windsor Windsor Canada

Both topography and buoyancy can drive groundwater flow;however,the interactions between them are still poorly understood.In this paper,the authors conduct numerical simulations of variable-density fluid flow and heat transport to quantify their relative importance.The finite element modeling experiments on a 2-D conceptual model reveal that the pattern of groundwater flow depends largely upon the relative magnitude of the flow rate due to topography alone and the flow rate due to buoyancy alone.When fluid velocity due to topography is greater than that due to buoyancy at large water table gradients,topography-driven 'forced convection' overwhelms buoyancy-driven 'free convection'.When flow velocity due to buoyancy is greater than that due to topography at small water table gradients,mixed free and forced convection takes place.In this case,free convection becomes dominant,but topography-driven flow still plays an important role since it pushes the free convection cells to migrate laterally in the downhill direction.Consequently,hydrothermal fluid flow remains changing periodically with time and no steady state can be reached.The presence of a low-permeability layer near the surface helps eliminate the topography effect on the underlying free convection.

关键词： hydrothermal flow free convection forced convection topography buoyancy finite element modeling

Seafloor topography and landform characteristics of Zengmu Shoal waters and their evolvement

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Acta Oceanologica Sinica 2004年第1期23卷 159-167页

作者： ZHANWenhuan TANGCheng ZHANGYixiang WANGPing ZHANGYechun ZHAOJunfeng SouthChinaSeaInstituteofOceanology ChineseAcademyofSciencesGuangzhou510301China

The topography data of the Zengmu Shoal and its adjacent area are acquired by the SeaBat-8111 multibeam system. The full survey covering over the Zengmu Shoal area gives us new knowledge about the area. It is a flat underwater platform consisting of coral reefs, its fathom line is like a trap in near SN direction and its shape is like an isosceles triangle with the acute angle pointing to the north. The east and west sides of the shoal are steep while its south side is more gentle. As viewed from geological evolution, the Zengmu Shoal is a typical biologic coral landform caused by tectonic uplift.

关键词： topography landform evolvement Zengmu Shoal

Numerical simulation of topography effects on the “00.7” severe rainfall in Beijing

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Progress in Natural Science:Materials International 2005年第9期15卷 818-826页

作者： ZHANG Chaolin1**, JI Chongping1, KUO Yinghwa2, FAN Shuiyong1, XUAN Chunyi3 and CHEN Min1(1. Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089, China 2. Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, CO 80307-3000, USA 3. Beijing Meteorological Bureau, Beijing 100089, China) Institute of Urban Meteorology China Meteorological Administration Beijing 100089 China Mesoscale and Microscale Meteorology Division National Center for Atmospheric Research Boulder CO 80307-3000 United States Beijing Meteorological Bureau Beijing 100089 China

In an effort to study the severe rainfall event of 4—5th July 2000 in Beijing (with 24h accumulated precipitation of 240 mm), we perform numerical simulations to investigate this event using the MM5v3.6 model. The model is initialized with the MM5/WRF 3DVAR analysis, which incorporates the ground-based GPS precipitable water vapor, automatic and conventional meteorological observations in its assimilation step. For 24 h accumulated precipitation forecast, the threat scores are 0.72, 0.76, 0.67 and 0.63, for thresholds of 1, 5, 10, and 20 mm, respectively. Holding other factors unchanged, sensitivity experiments were conducted with different topographic resolutions of 110, 50 and 3.7 km to investigate the topographic effects on precipitation over the Beijing area. In these sensitivity experiments, we attempt to preserve the realistic orographic distribution in the model topography under the condition of keeping the dynamic-thermodynamic consistency of the initial model atmosphere to the extent possible. Results indicate that the unique topographic distribution and variations in the Beijing area play an important role in determining the location, distribution and intensity of heavy precipitation.

关键词： topography heavy rainfall 3DVAR ground-based GPS numerical simulation.

New Method for Estimating Daily Global Solar Radiation over Sloped topography in China

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Advances in Atmospheric Sciences 2018年第3期35卷 285-295页

作者： Guoping SHI Xinfa QIU Yan ZENG School of Geography and Remote Sensing Nanjing University of Information Science and Technology Nanjing 210044 China School of Applied Meteorology Nanjing University of Information Science and Technology Nanjing 210044 China jiangsu Climate Center Nanjing 210009 China

A new scheme for the estimation of daily global solar radiation over sloped topography in China is developed based on the Iqbal model C and MODIS cloud fraction. The effects of topography are determined using a digital elevation model. The scheme is tested using observations of solar radiation at 98 stations in China, and the results show that the mean absolute bias error is 1.51 MJ m-2 d-1 and the mean relative absolute bias error is 10.57%. Based on calculations using this scheme, the distribution of daily global solar radiation over slopes in China on four days in the middle of each season （15 January, 15 April, 15 July and 15 October 2003） at a spatial resolution of 1 km×1 km are analyzed. To investigate the effects of topography on global solar radiation, the results determined in four mountains areas （Tianshan, Kunlun Mountains, Qinling, and Nanling） are discussed, and the typical characteristics of solar radiation over sloped surfaces revealed. In general, the new scheme can produce reasonable characteristics of solar radiation distribution at a high spatial resolution in mountain areas, which will be useful in analyses of mountain climate and planning for agricultural production.

关键词： sloped terrain solar radiation topography geographic information system

The elusive mantle dynamic topography

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Science China Earth Sciences 2020年第2期63卷 312-314页

作者： Lijun LIU Department of Geology University of Illinois at Urbana-Champaign

The Earth's surface is characterized by a bi-modal distribution of topography,where continents on average are about 5 km higher than the ocean basins.This basic topographic property of the planet Earth could be intuitively explained by isostasy,in that the felsic・to・intermediate continental crust is thick(~40 km)and light(~2.8 g/cm3)while the mafic oceanic crust is thin(〜7 km)and dense(〜3 g/cm3).There are also large-scale topographic variations within continents and oceans,which could also be attributed to isostasy:the former is usually due to lateral variation in crustal thickness and the latter to different ages of the seafloor.Since it seems isostasy works just fine for most large-scale topographic features on Earth,why do we bother to further introduce dynamic topography?

关键词： topography topographic Earth