Footpath morphology and terrain sensitivity on high plateaux: the Mamore Mountains,Western Highlands of Scotland

Variations in the morphology of a high‐level footpath are characterized using a new approach that relates footpath morphology to six terrain units defined jointly by two contrasting plant communities (U7 grass–heath communities dominated by Nardus stricta and Carex bigelowii, and U10 moss–heath communities dominated by Carex bigelowii and Racomitrium lanuginosum) and by the contrasting textural characteristics of underlying mineral soils developed on schist, granite and quartzite. All six terrain units are characterized by distinct footpath morphologies. The most critical factor affecting footpath morphology is the shear strength of the vegetation mat and underlying root zone. Vegetation mat shear strength was measured using a specially constructed shear rake. On all three lithologies, median shear strengths for U7 communities significantly exceed those for U10 communities, so that pathways on the former are significantly narrower and deeper than those developed on the latter. Adjacent zones of damaged or modified vegetation cover are also wider on U10 communities. The role of mineral soil (regolith) texture and thus underlying lithology in controlling footpath morphology is more complex. For soils with abundant fines, granite soils have lower shearing resistance than schist soils, and are associated with wider footpaths. Footpaths are also wide on clast‐supported quartzite regolith, which has high shearing resistance: pathways are trapezoidal in cross‐section in areas of U7 vegetation cover, but footpaths are very broad and diffuse in areas of U10 cover. Pathway depths are limited by increasing shear and compressive strength with depth. Implications of these findings for further research and management strategies are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

The Kwinana Coastal Fumigation Study: III – Meteorological and Turbulence Modelling on Selected Days

The Kwinana Coastal Fumigation Study took place inearly 1995 at Kwinana near Perth in Western Australia.The study involved surface and elevated meteorologicaland plume fumigation measurements in sea-breeze flowsnear the coast, and has yielded a comprehensive dataset that is suitable for assessing meteorological andplume dispersion models. In this paper, wesimulate the meteorology and turbulence on four casestudy days, and compare model results with thedetailed surface and aircraft measurements takenduring the study. These days had surface synopticwinds ranging from southerly to northeasterly, witheither stable or near-neutral temperature profilesover the sea.The model used was based on that developed by Hurley(Boundary-Layer Meteorol. 83, 43–73, 1997), but extended here to allow domain nesting,optional non-hydrostatic simulations, and a vegetativecanopy at the surface. The model was forced bystandard weather service synoptic data, and thesimulations have captured the essential features ofthe strong sea-breeze circulation observed on thesedays. The boundary-layer structure over the sea waspredicted to be near-neutral or stable in agreementwith the observations on the particular day. The windspeed and direction in the sea-breeze flow weregenerally predicted well, although the predictedmaximum inflow speed over the land was a little toohigh. The potential temperature was generallyover-predicted, but temperature gradients agreed well.Predicted turbulence levels in the bottom-half of thethermal internal boundary layer compared well to theobservations, but under-estimated the observations inthe in the upper half of this layer. Near-surfacemeasurements of meteorological variables werepredicted well over the entire diurnal cycle, althoughthe predicted sea-breeze onset was generally tooearly. A quantitative model evaluation for thenear-surface sites showed the model performance to bebetter than that from other studies, with Index ofAgreement (IOA) values of 0.8 (wind speed) and 0.96(temperature), compared with values of 0.5–0.6 (windspeed) and 0.33 (temperature) obtained from otherstudies.The availability of new higher resolution synopticanalyses should obviate the lack of spatial andtemporal resolution in synoptic inputs. Theincorporation of these higher resolution synopticinputs and new parameterisation schemes should improvefuture model performance.     

华南沿海2011年7月15—18日持续暴雨过程中的季风槽与中尺度对流系统相互作用

应用NCEP FNL再分析资料及位涡分离反演等方法,对华南沿海2011年7月15—18日持续暴雨过程中季风槽与中尺度对流系统的相互作用进行了研究,主要针对暴雨发生期间季风槽气旋性涡度向上发展的机理及其对季风槽维持发展和中尺度对流系统活动的影响进行分析。结果发现,季风槽的中尺度对流系统发展于弱斜压性环境中,大多在槽东西两端涡度中心区发展最强。南侧盛行的西南低空急流为对流反复发生提供了对流发展的“可维持性”条件,是对流得以组织发展成为中尺度对流系统的重要原因。涡度收支诊断表明,季风槽气旋性涡度生成主要由中尺度对流系统低层辐合引起。位涡分离反演结果证实,季风槽气旋性环流增强主要由与中尺度对流系统潜热加热相关的扰动位涡造成,并随着中尺度对流系统加热峰值高度升高而向上发展,是大尺度环流对中尺度对流系统潜热加热动力响应的结果。在季风槽东西两端,由于中尺度对流系统发展强烈且持续,具有更高的加热效率,引起的气旋性涡度向上发展最为明显。其结果可引起中尺度对流系统西南一侧向北非地转风发展,并在地转偏向力作用下增强西风,维持低空急流的发展,为对流反复发生提供条件。这些都说明季风槽大尺度环流与中尺度对流系统相互作用在中尺度对流系统和持续暴雨形成过程中有重要作用。     

中尺度模式中的边界层特征量分析

在中尺度数值天气预报模式MM4中，用level3及E-ε-l两种湍流闭合方法对原总体边界层参数化方案进行改进，使得中尺度模式中可以直接输出有关湍流量，并对地表通量参数化方案进行改进，进而对不同下势需如沙漠，植被上的有关湍流量和边界层特征量进行分析。研究中尺度系统中边界层结构的特征，本文主要从地表通量，湍流交换系数，湍流动能（q^2)，温度脉动方差（θ^2)及风温廓线等几个方面进行研究，结果表明，新方案能更好地反映边界层特征。     

顾及地形起伏的无人机影像覆盖分析方法

使用无人机实施测绘航空摄影时,由于无人机相对航高较低,地面起伏会对无人机影像的分辨率、覆盖范围、重叠度造成较大的影响,影像成果会出现分辨率不足、重叠度不够、覆盖漏洞等缺陷。针对这一情况,本文提出了一种利用数字微分正解法的计算方法,借助DEM准确计算每张影像的覆盖范围,并使用FME软件高效生成全部影像的覆盖范围。经过实际使用,验证了该方法可以在航线设计阶段准确预测并分析全部影像的覆盖范围、重叠度,因此可及时发现设计问题并调整航线。该方法可以有效减少因地形起伏造成的影像覆盖缺陷,减少返工现象,从整体上提高了作业效率。     

Use of terrestrial photogrammetry for monitoring and measuring bank erosion

This paper examines the use of terrestrial photogrammetry as a technique for measuring bank erosion in a rapidly changing fluvial environment. It has been recognized that there are a number of advantages when applying photogrammetric techniques to geomorphological situations. In this study the enhancement of spatial sampling combined with the ability to capture additional information, such as soil moisture, on film, is of particular importance in enabling the identification of specific processes involved in bank erosion as well as detailed volumetric analysis of losses. Metric terrestrial photography was taken of the river bank on several dates, and data were abstracted by the use of analytical photogrammetry. This enabled the generation of digital terrain models from which morphological and volumetric changes could be assessed. © 1997 John Wiley & Sons, Ltd.     

Surface circulation of the Levantine Basin: Comparison of model results with observations

The eastern Mediterranean (Levantine Basin) hydrography and circulation are investigated by comparing the results of a high-resolution primitive equation model with observations. After a 10-year integration, the model is able to reproduce the major water masses and the circulation patterns of the eastern Mediterranean. Comparisons with the POEM hydrographical observations show good agreement. The vertical distribution of the water masses matches that of the observations quite well in terms of monthly mean. The model surface circulation is in agreement with circulation schemes derived from recent observations. Some well-known mesoscale features of the upper thermocline circulation are also realistically reproduced. In agreement with satellite observations, the model shows that high-energy mesoscale eddies dominate the upper thermocline circulation in the southern and the central parts of the Levantine Basin. Most of the Atlantic Water follows the north African coast and forms a strong coastal jet near the Libyan coast rather than forming the Mid-Mediterranean Jet described by several authors. The sub-basin circulation shows a strong seasonal signal. A strong and stable current flows along the isobaths in winter, becoming weaker and with more meanders in summer. The mesoscale eddies throughout the whole basin are more energetic in summer than in winter.     

非对称型强飓风中的准平衡流特征分析Ⅱ:波动结构

利用非对称波分量分解和小波分析的方法,对准平衡动力模型下非对称强飓风内中尺度波动的空间结构和时间序列特征进行分析.结果表明,平衡流场中1波扰动占主要地位且具有涡旋Rossby波的典型结构特征,准平衡流各波数下扰动的空间分布反映了中尺度波动的混合性质;模式大气和准平衡垂直运动的全局功率谱中,超过信度检验的强波动信号中不仅包含分别表征重力波和涡旋Rossby波的高频和低频波动信号,还存在表征具有物理性质不可分特性的混合涡旋Rossby-重力波的中频波动.混合波的出现建立了不同频段波动之间的能量交换通道,其信号的变化对飓风系统的强弱变化具有一定的指示作用.非平衡垂直运动的波动强信号则主要集中在高频和低频区域,反映了在飓风强度变化情况下,与高频重力波有关的快波调整过程所引起的垂直扰动的振荡和传播.强垂直风切变对飓风内中尺度波动的切向和径向传播具有重要影响,当环境垂直风切变很强时,准平衡1波扰动在径向和切向方向上均呈驻波形态,随着环境垂直风切变的减弱,1波扰动以混合波波速逆基本气流传播.