中国黄海西岸海陆风循环结构研究          下载免费PDF全文

Yongxiang Ma  Jinyuan Xin  Xiaoling Zhang  Lindong Dai  Klaus Schaefer  Shigong Wang  Yuesi Wang  Zifa Wang  Fangkun Wu  Xinrui Wu  Guangzhou Fan 《大气和海洋科学快报》2021,14(1):14-21

陆海风是由于海陆表面之间的比热容不同而导致的昼夜热量分布差异,从而在海岸附近引发的大气中尺度循环系统.本文利用多普勒风激光雷达Windcube100s首次对黄海西海岸的海陆风的循环结构进行了观测研究.在2018年8月31日至9月28日观测期间发现,海陆风发展高度一般在700 m至1300 m.海陆风转化持续的时间为6小时至8小时.在425m高度,海风水平风速出现最大值,平均为5.6 m s-1.陆风最大水平风速出现在370m,约为4.5 m s-1.最大风切变指数在1300m处,为2.84;在陆风向海风转换过程中,最大风切变指数在700m处,为1.28.在同一高度上,风切变指数在海风盛行和陆风盛行时的差值范围为0.2-3.6,风切变能反映出海陆风的发展高度.  相似文献   

Automated extraction of hydrographically corrected contours for the conterminous United States: the US Geological Survey US Topo product     

Samantha T. Arundel  Philip T. Thiem  Eric W. Constance 《制图学和地理信息科学》2018,45(1):31-55

The US Topo is a new generation of digital topographic maps delivered by the US Geological Survey (USGS). These maps include contours in the traditional 7.5-min quadrangle format. The process for producing digital elevation contours has evolved over several years, but automated production of contours for the US Topo product began in 2010. This process, which is quite complex yet fairly elegant, automatically chooses the proper USGS quadrangle, captures the corresponding 1/3 as grid points from the national elevation data set (3D Elevation Program), and adjusts elevation data to better fit water features from the National Hydrography Dataset. After additional processing, such as identifying and tagging depressions, constructing proper contours across double-line streams, and omitting contours from water bodies, contours are automatically produced for the quadrangle. The resulting contours are then compared to the contours on the original (legacy) topographic map sheets, or to the 10-m contours from the original map sheets. Where the elevation surface used to generate the contours has been derived from the previously published contours for a quadrangle, the generated contours match the legacy contours quite well. Where newer elevation sources, such as lidar, originate the elevation surface, generated contours may vary significantly from the previous cartographically produced contours due to more accurate representations of the surface, and less reliance on cartographic interpretation.  相似文献   

Global, 30-m resolution continuous fields of tree cover: Landsat-based rescaling of MODIS vegetation continuous fields with lidar-based estimates of error   总被引：1，自引：0，他引：1  

《International Journal of Digital Earth》2013,6(5):427-448

Abstract

We developed a global, 30-m resolution dataset of percent tree cover by rescaling the 250-m MOderate-resolution Imaging Spectroradiometer (MODIS) Vegetation Continuous Fields (VCF) Tree Cover layer using circa- 2000 and 2005 Landsat images, incorporating the MODIS Cropland Layer to improve accuracy in agricultural areas. Resulting Landsat-based estimates maintained consistency with the MODIS VCF in both epochs (RMSE =8.6% in 2000 and 11.9% in 2005), but showed improved accuracy in agricultural areas and increased discrimination of small forest patches. Against lidar measurements, the Landsat-based estimates exhibited accuracy slightly less than that of the MODIS VCF (RMSE=16.8% for MODIS-based vs. 17.4% for Landsat-based estimates), but RMSE of Landsat estimates was 3.3 percentage points lower than that of the MODIS data in an agricultural region. The Landsat data retained the saturation artifact of the MODIS VCF at greater than or equal to 80% tree cover but showed greater potential for removal of errors through calibration to lidar, with post-calibration RMSE of 9.4% compared to 13.5% in MODIS estimates. Provided for free download at the Global Land Cover Facility (GLCF) website (www.landcover.org), the 30-m resolution GLCF tree cover dataset is the highest-resolution multi-temporal depiction of Earth's tree cover available to the Earth science community.  相似文献   

From Zipf's law to hypsometry: seeking the ‘signature’ of elevation distribution     

Lan Mu 《International journal of geographical information science》2013,27(7):1312-1328

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A 14-year monthly climatology and trend in the 35–65 km altitude range from Rayleigh Lidar temperature measurements at a low latitude station     

Paulo P. Batista  Barclay R. Clemesha  Dale M. Simonich 《Journal of Atmospheric and Solar》2009,71(13):1456-1462

A sodium resonance lidar at 589 nm has been operated in São José dos Campos, Brazil (23°S, 46°W) since 1972 mainly for studies related to the origin, chemistry and dynamics of the mesospheric sodium layer. Beginning in 1993, the improved laser capability has also enabled the processing of the Rayleigh signal from which the temperatures from 35 to 65 km are retrieved on a nightly mean basis. We used these nightly profiles to determine the monthly temperature profiles from 1993 to 2006. The mean temperature characteristics for each year and for the whole period are obtained. Seasonal thermal amplitude is small (6 K peak to peak at 40 and 60 km). Compared with the MSISE-90 model, a large difference is noted, with temperature lower than the model below the stratopause and higher above. Also the seasonal variation has a large difference with better agreement occurring around local winter, but with temperatures higher by 8–10 K at the equinoxes. The semiannual component is dominant over the annual at all altitudes. Linear trends with decreasing temperature of 1.09, 2.29 and 1.42 K/decade are observed at 40, 50 and 60 km, respectively.  相似文献   

利用瑞利激光雷达观测北京地区上平流层地形重力波活动   总被引：4，自引：0，他引：4       下载免费PDF全文

郭文杰  胡雄  闫召爱  郭商勇  程永强  杨钧烽 《地球物理学报》2015,58(10):3481-3486

本文利用中国科学院空间科学与应用研究中心的瑞利激光雷达首次观测到了平流层地形重力波活动的现象,并结合美国国家环境预报中心(NCEP)的全球预报系统(GFS)的风场数据分析了该地形重力波的基本参数.与惯性重力波相比较,地形重力波的密度扰动没有下传的相位,在同一高度上,其扰动相位保持不变.北京空间科学与应用研究中心瑞利激光雷达自2012年开始观测实验以来,已经观测到多起地形重力波活动事件.本文以2013年11月11日的观测数据为例,研究北京上空的地形重力波活动,并结合GFS风场数据分析了北京上平流层地形重力波的波长、传播方向、传播速度等参量.通过分析得到在2013年11月11日北京上空存在一列传播方向为北偏西52.4°,水平波长为5.5km,平均垂直波长约为6.0km的地形重力波.  相似文献   

Bank erosion of legacy sediment at the transition from vertical to lateral stream incision          下载免费PDF全文

Nathan J. Lyons  Michael J. Starek  Karl W. Wegmann  Helena Mitasova 《地球表面变化过程与地形》2015,40(13):1764-1778

Streambank erosion is a primary source of suspended sediments in many waterways of the US Atlantic Piedmont. This problem is exacerbated where banks are comprised of fine sediment produced by the intensive land use practices of early European settlers. A stream in this region, Richland Creek incises into banks comprised of three stratigraphic layers associated with historic land use: pre‐European settlement, early European agriculture and development, and water‐powered milldam operation. This study aims to identify the bank processes along a reach of Richland Creek that is eroding towards its pre‐disturbance elevation. The volume of material that has eroded along this stream since the milldam breached was calculated by differencing a reconstructed surface of the pond bed and an aerial lidar digital terrain model (DTM). Immediately downstream from the study reach, the channel is floored by bedrock and immediately upstream the rate of channel erosion approximately doubled along the longitudinal profile of Richland Creek, which indicate that the study reach spans the transition from a channel dominated by vertical incision in the upstream direction to horizontal widening in the downstream direction. The combined hydrometeorological conditions and dominant processes causing reach‐scale cut bank erosion were investigated with analyses of stream stage, precipitation, and streambank volumetric and surfaces change that was measured during nine terrestrial lidar surveys in 2010–2012. The spatial variability of erosion during a simulated precipitation event was examined in a field‐based experiment. Erosion was greatest where mill pond sediment columns detached along vertical desiccation and horizontal seepage cracks. This sediment accumulated on the bank toe throughout the study and was a source of readily‐entrained fine sediment contrary to the upper reaches where depositional accommodation space is more limited. Findings suggest that hotspots of sediment excavation progress upstream, indicating that restoration efforts should focus upon stabilizing banks at these locations. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Modelling Internal Boundary-Layer Development in a Region with a Complex Coastline   总被引：1，自引：1，他引：0  

Ekaterina Batchvarova  Xiaoming Cai  Sven-Erik Gryning  Douw Steyn 《Boundary-Layer Meteorology》1999,90(1):1-20

The purpose of this paper is to test the ability of two quite different models to simulate the combined spatial and temporal variability of the internal boundary layer in an area of complex terrain and coastline during one day. The simple applied slab model of Gryning and Batchvarova, and the Colorado State University Regional Atmospheric Modelling System (CSU-RAMS) are tested by comparison with data gathered during a field study (called Pacific '93) of photochemical pollution in the Lower Fraser Valley of British Columbia, Canada. The data utilised here are drawn from tethered balloon flights, free flying balloon ascents, and downlooking lidar operated from an aircraft flown at roughly 3500 m above sea level. Both models are found to represent the temporal and spatial development of the internal boundary-layer depth over the Lower Fraser Valley very well, and reproduce many of the finer details revealed by the measurements.  相似文献   

Introduction to the themed issue: Wildfire and Geomorphic Systems          下载免费PDF全文

Ellen Wohl 《地球表面变化过程与地形》2018,43(7):1542-1546

Wildfires alter fluxes of water, sediment, solutes, and organic matter in ways that can be transient or persistent. Alterations in material flux then impact geomorphic processes and landforms in a manner that can also be transient or persistent and that can involve complex response. This themed issue includes papers that document distinctive geomorphic responses in the upland and channel components of forested landscapes in southern Europe, northern Australia, and the western United States. Among the themes that emerge from the collected papers are: (i) the importance of ongoing technological developments, including real‐time instrumentation, ground‐based and aerial remote sensing, isotopic ratios, and numerical models of landscape processes, for documenting and predicting fire‐related geomorphic processes; and (ii) the great uncertainties about future landscape change in a global environment of rapidly changing climate and growing human populations that encroach onto remaining wildlands in fire‐susceptible regions. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

The influence of DEM resolution on simulated solar radiation‐induced glacier melt     

Chris Hopkinson  Laura Chasmer  Scott Munro  Michael N. Demuth 《水文研究》2010,24(6):775-788

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