基于DEM的地形高度与土地利用空间格局的关系——以韶关市大塘镇为例

地形高度是影响土地利用空间格局分布的影响因素之一,本文以韶关市大塘镇为研究区,基于研究区的DEM和土地利用现状图,利用GIS提取研究区的地形高程及土地利用信息,并将各地形高度与土地利用图进行叠加分析,研究地形高度与土地利用空间格局的关系。研究结果表明:1随着高程增加,各土地利用类型的面积及占土地总面积的比例都呈下降趋势;2土地利用类型占该该类土地利用的比重均在第一级高程或第二级高程达到最大值,随高程增加,分布比重逐渐下降;3低高程区域土地利用较为破碎,高高程区域土地利用较为集中,以林地为主。     

不确定性引导下的地形简化方法研究

提出一种不确定性引导下的地形简化方法。该方法利用地统计方法中特有的方差统计量对简化结果的不确定性进行量化评估,并以此作为优化目标进行地形简化操作。实验部分,从高程精度、地表基本形态以及骨架保留度三方面对新方法的有效性进行验证。结果表明:与传统的特征简化方法相比,新方法在控制地形简化的不确定性的前提下很好地保持了地形简化精度以及原始地表的骨架结构。     

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GRAPES-Mesov3.1在西南地区2011年汛期的预报检验分析

基于GRAPES-Mesov3.1模式建立的GRAPES-Meso中尺度模式系统在西南区域气象中心运行稳定,该系统于2011年5月投入试验运行。应用GRAPES模式分析产品,NCEP的1°×1°再分析资料,实况资料以及2011年西南低涡探空加密观测资料等,对2011年汛期GRAPES-Meso系统的预报进行统计检验与天气过程分析。结果表明,模式对2011年8月川渝持续高温、9月16~18日四川东北部大暴雨等高影响天气过程有较强的预报能力,这对实际天气预报有着积极的指导意义。预报与实况偏差主要表现在模式通常超报云南地区降水,而对西南其他地区易漏报。模式通常低报青藏高原到四川西部气温,高报四川东部及重庆地区气温。预报高度场持续偏低,西南低空急流预报偏强,对流层中低层比湿偏低,这些可能是造成降水强度偏弱、降水落区偏北、强降水落区偏小的主要原因。对流层中低层高度场持续偏低,低空急流偏强与模式温度预报偏高和加热不均匀有关。同时模式对平原地区较高原山地预报要好,误差通常随等压面高度降低而增大,在一定程度上表明复杂地形对模式预报影响较大。     

Turbulence intensity and turbulent kinetic energy parameters over a heterogeneous terrain of Loess Plateau

A deep understanding of turbulence structure is important for investigating the characteristics of the atmospheric boundary layer, especially over heterogeneous terrain. In the present study, turbulence intensity and turbulent kinetic energy (TKE) parameters are analyzed for different conditions with respect to stability, wind direction and wind speed over a valley region of the Loess Plateau of China during December 2003 and January 2004. The purpose of the study is to examine whether the observed turbulence intensity and TKE parameters satisfy Monin-Obukhov similarity theory (MOST), and analyze the wind shear effect on, and thermal buoyancy function of, the TKE, despite the terrain heterogeneity. The results demonstrate that the normalized intensity of turbulence follows MOST for all stability in the horizontal and vertical directions, as well as the normalized TKE in the horizontal direction. The shear effect of the wind speed in the Loess Plateau region is strong in winter and could enhance turbulence for all stability conditions. During daytime, the buoyancy and shear effect together constitute the generation of TKE under unstable conditions. At night, the contribution of buoyancy to TKE is relatively small, and mechanical shearing is the main production form of turbulence.     

北京“7.21”暴雨的不稳定性及其触发机制分析

本文利用WRF模拟的高分辨率资料对2012年7月21日北京特大暴雨过程的对流不稳定和条件对称不稳定性及其触发和维持机制进行了诊断分析。分析结果表明:(1)在临近暴雨发生时刻及暴雨初期, 大气低层主要以对流不稳定为主, 随后对流触发, 不稳定性减弱, 而低空急流和湿斜压性的增强, 使得条件性对称不稳定加强, 维持和加强了暴雨的不稳定性。(2)分析表明, 在暴雨过程中主要由于较强的水平风的垂直切变造成湿位涡的斜压分量异常, 从而导致条件性对称不稳定的产生。(3)本文分别对暴雨发生过程中的对流不稳定与条件对称不稳定的触发机制进行了分析, 主要结论如下:暴雨初期对流性降水阶段, 切变线上有利的垂直上升环境与地形的强迫抬升相互配合, 触发了对流性降水。另外, 北京上空的干冷空气入侵, 也增强了大气的对流不稳定性, 更易触发对流;对称不稳定导致的降水阶段, 主要是由于北京上空冷暖空气的长期对峙, 冷空气逐渐深入到暖湿空气下方, 使得暖湿气团沿冷气团爬升, 从而触发对称不稳定, 造成持续性降水。此次暴雨过程中0900～1300 UTC时刻暴雨增幅的重要原因是0900 UTC北京风向突变, 转为偏东风, 且风速骤增, 北京西北侧的喇叭口状的地形的强迫抬升作用, 与上空750 hPa移来的切变线上的垂直运动相互叠加, 形成中尺度涡旋, 产生了强烈的上升运动, 触发不稳定, 产生大暴雨。     

金活动态测量法在红壤区与干旱黄土区找矿中的应用

用金属活动态提取法在广西与山西黄土区进行试验研究,发现在山西黄土区,利用金的水提取态含量偏低,异常不明显,而金的粘土结合态、有机物结合态和铁锰氧化物结合态异常清晰地反映在矿体上方;而在雨量充沛的广西红壤区,金的水提取态和铁锰氧化物结合态异常较好,而粘土结合态金异常效果不太理想。研究结果表明在这两个地区应用金属活动态测量法进行找矿研究时,可以对其提取有利的相态来进行靶位确定。     

On the definition of the flow width for calculating specific catchment area patterns from gridded elevation data

Specific catchment area (SCA) patterns are commonly computed on grids using flow direction algorithms that treat the flow as coming from a point source at the pixel centre. These algorithms are all ambiguous in the definition of the flow width to be associated with a pixel when computing the SCA. Different methods for computing the flow width have been suggested, without giving an objective reason. In the few cases where this issue has been specifically discussed, the flow width is derived from subjective analysis and incorrect conceptualizations. This paper evaluates alternative approaches for defining the flow width when computing SCA patterns using the D∞ and D8 algorithms, by comparing theoretical and computed SCA patterns on sloping planes, inward and outward cones. Two new methods of defining the flow width are also analysed for both the D∞ and D8 algorithms. The performances of the different methods are discussed in relation to two dimensionless parameters: (1) the global resolution, defined as the ratio of a characteristic length of the study area to the grid size and (2) the upslope area resolution, defined as the ratio of the theoretical SCA to the grid size. The optimal methods are identified by specific threshold values of these dimensionless parameters. We conclude that assuming the flow width invariant and equal to the grid size is generally the best approach in most practical circumstances, both for the D∞ and D8 algorithm. Copyright © 2005 John Wiley & Sons, Ltd.