Effects of initial step height on the headcut erosion of bank gullies: a case study using a 3D photo-reconstruction method in the dry-hot valley region of southwest China

Abstract

Headcut erosion has been recognized as one of the main processes involved in gully development in the dry-hot valley region of southwest China. To examine the effect of initial step height on headcut erosion processes, three headcuts were constructed ranging in height from 0.75 to 1.25 m on an active bank gully head, and a series of scouring experiments were conducted under a flow discharge of 120 L min^?1. The morphological evolutions of the plunge pools and soil loss volume were estimated by three-dimensional photo-reconstruction methods (3D-PR). As the step height increased, the experimental results showed that: (1) the transformed potential energy and shear stress would increase by approximately 4.89 J s^?1 and 26.4 Pa on average when the step height increased 0.25 m; (2) the mean depth and width of the plunge pool exhibited obvious growth, and the morphology of the cross-section developed from approximately V-shaped to U-shaped; and (3) soil loss volume increased logarithmically, with total soil loss volumes of 0.076, 0.105 and 0.116 m³, respectively. Although the significant effects of the initial step height on headcut erosion were verified, further quantitative studies are required to quantify the mechanism of headcut erosion, especially for plunge pool erosion.     

The Pedagogical Benefits of SimCity in Urban Geography Education

This article investigated the pedagogical potential of the SimCity simulation game in an urban geography course. University students used SimCity to build their own cities and applied a wide range of theories to support their urban structures. Moreover, the students critically evaluated the logic and functioning of the SimCity simulation compared to real-world contexts and urban geography principles. The students believed the SimCity activity provided them with opportunities to promote their geographic creativity, resulting in diverse, unique, and interesting cities. The findings demonstrate that the use of SimCity can be an effective tool for geography education.     

Comparative analysis of significant wave height between a new Southern Ocean buoy and satellite altimeter

中国于2019年第35次南极考察中,首次在南大洋布放了锚系实时综合观测浮标(西风带海洋环境监测浮标,WEMB),为深入了解此海区的海洋环境变化提供了宝贵资料.国家海洋技术中心WEMB研究团队基于AVISO公开发布的多颗卫星高度计L3产品,通过数据配对,误差统计和最小二乘线性拟合等方法,对西风带海洋环境监测浮标的有效波高数据误差进行了分析与校正.校正后的浮标有效波高统计显示西风带常年处于大浪以上海况,观测期间内57％处于巨浪海况,并且伴随有高度相关的大风天气.     

关键元素与生命健康:中国耕地缺硒吗?

地球上的生命和非生命都是由自然界已发现的92种化学元素组成的,通过全国土壤地球化学基准值与人体血液元素含量对比研究,发现血液中40~50种化学元素平均值与土壤地球化学基准值的分布高度一致,表明这些关键元素与生命息息相关。近年大家持续关注的硒(Se)元素是人体必需的微量元素,缺乏会产生健康风险,但摄入过量也会导致中毒,因此被称为健康窗口元素。过去研究认为,中国耕地缺硒是造成健康危害的原因之一。本文通过对全国3 382个网格化点位土壤采样,获得Se的地球化学基准值和空间分布数据,发现中国贫硒国土面积,按照世界卫生组织推荐值(0.1 mg/kg)和中国规范(0.125 mg/kg)计算,分别占21.1%和31.6%;适宜区(0.125~0.40 mg/kg)面积大约555万km²,占国土面积约57.1%;富硒区(>0.40 mg/kg)面积达110万km²,占国土面积约11.2%。贫硒国土主要分布在青藏高原和内蒙古局部地区,而中国9大平原的粮食主产区耕地总体上不缺硒,其中珠江三角洲平原、广西平原、成都平原、长江中下游平原是富硒区(>0.40 mg/kg),华北平原、东北平原、三江平原、关中平原是硒边缘区-适量区(0.125~0.40 mg/kg),只有河套平原是缺硒区(<0.125 mg/kg)。根据覆盖全国的网格化土壤采样分析结果,发现低硒带呈不连续的片状分布于内蒙古东部至青藏高原一带,与传统认为“低硒带分布于东北三省至西南云贵高原”不完全一致。硒的空间分布模式主要受地质背景、岩石类型、土壤类型和自然地理景观控制。     

Main Detrainment Height of Deep Convection Systems over the Tibetan Plateau and Its Southern Slope

Deep convection systems (DCSs) can rapidly lift water vapor and other pollutants from the lower troposphere to the upper troposphere and lower stratosphere. The main detrainment height determines the level to which the air parcel is lifted. We analyzed the main detrainment height over the Tibetan Plateau and its southern slope based on the CloudSat Cloud Profiling Radar 2B_GEOPROF dataset and the Aura Microwave Limb Sounder Level 2 cloud ice product onboard the A-train constellation of Earth-observing satellites. It was found that the DCSs over the Tibetan Plateau and its southern slope have a higher main detrainment height (about 10?16 km) than other regions in the same latitude. The mean main detrainment heights are 12.9 and 13.3 km over the Tibetan Plateau and its southern slope, respectively. The cloud ice water path decreases by 16.8% after excluding the influences of DCSs, and the height with the maximum increase in cloud ice water content is located at 178 hPa (about 13 km). The main detrainment height and outflow horizontal range are higher and larger over the central and eastern Tibetan Plateau, the west of the southern slope, and the southeastern edge of the Tibetan Plateau than that over the northwestern Tibetan Plateau. The main detrainment height and outflow horizontal range are lower and broader at nighttime than during daytime.     

2018年常州一次罕见持续性雾-霾天气分析

利用常规气象观测资料、探空资料、污染物浓度及AQI资料、NCEP再分析资料等,对2018年11月24日至12月3日夜间常州持续11 d的强浓雾和严重霾天气过程进行了分析。结果表明：（1）此次雾-霾过程持续时间长、范围广、强度大、污染重。（2）中纬度地区高层持续纬向环流控制、中低层暖脊稳定存在,地面持续受均压场或弱倒槽顶部、弱冷锋前部影响,是这次持续性雾-霾过程的重要天气条件。（3）边界层内弱辐散、负涡度及弱的下沉气流是此次雾-霾天气得以长时间维持、发展的动力因子。近地层长时间水汽饱和且维持小风速利于雾-霾的长时间维持。（4）近地面高强度的贴地逆温长时间维持和持续较低的混合层高度是此次雾-霾形成、发展和长时间维持的重要热力条件。雾比霾的平均混合层高度明显偏低且霾等级越高混合层高度越低,混合层高度的变化先于能见度变化,对雾-霾临近预警有较好的指导作用。（5）弱冷空气渗透、风速适当增加、混合层高度的先期快速下降、负净辐射曝辐量绝对值的明显增大是雾爆发性增强的主要原因。     

2017年5月7日广州特大暴雨模拟中的背景场影响分析

2017年5月7日广州发生了特大暴雨,为研究不同背景场资料对这次暴雨过程的影响,模式背景场分别采用美国NCEP的GFS资料和中国的T639资料,利用GRAPES_Meso模式对这次暴雨过程进行了数值模拟和影响分析;数值试验结果表明,采用不同的背景场对这次暴雨过程具有显著影响,用T639资料(T639_run)作为模式背景场大致模拟出了这次暴雨过程,而采用NCEP GFS数据(GFS_run)模拟的降水明显偏北。其原因是,采用T639资料做背景场时,华南暴雨区域存在深厚的水汽输送,同时存在强烈的上升运动,可以产生极端强降水;而采用GFS资料进行数值模拟时,实际暴雨区上空的上升气流较弱,水汽输送也较弱,使强降水落区偏北。GRAPES_Meso模式模拟的华南地区的云顶高度整体偏高,云顶温度整体偏低,相对来说,采用T639_run的模拟结果优于GFSrun的结果,该研究结果可以为云降水方案中的水物质和云量计算方案的改进和优化提供一定的参考。     

公路勘测中应注意的几个问题

结合营口滨海大道勘测设计工程实例,探讨了公路勘测时坐标系统选择、平面控制点点位选定、全站仪三角高程代替四等水准、RTK技术应用等一些问题,并提出了几点结论。     

批判实在论在城市空间研究中的应用

批判实在论是一种有关社会科学的哲学理论,它从浅显易懂的本体论出发,抨击了传统科学研究中背离客观实在的种种理想主义倾向,如对“规律性”的迷信、对计量分析方法的过分依赖等。在上世纪80年代批判实在论被引入到西方城市空间研究中、发展为一种新的研究范式,该范式在对传统空间分析研究的批判基础上强调对空间现象的因果机制的阐释,提出了有关因果机制的概念框架,认为只有透过错综复杂的因果关系去把握决定事物的深层结构和机制,才能避免传统研究中常出现的“混乱归因”现象,为此发展了具体研究和抽象研究、深入研究和广泛研究相结合的研究方法,并将其应用于城市空间研究实践中。本研究对批判实在论范式的产生背景和哲学基础等进行了分析,介绍了其理论脉络、方法论和研究实践,并对该范式进行了评价。