Reconstruction of the late Quaternary environment of the lower Luni Plains,Thar Desert,India

Geomorphological processes in the Thar Desert of India are largely climate driven. In the lower reaches of the River Luni (the only major drainage system in the Thar Desert) a fluvio‐aeolian sequence was located at a site called Khudala. Sediments of this sequence represented a variety of depositional environments, namely aeolian, fluvially reworked aeolian, overbank deposits, gravels, and occasional evidence of pedogenesis. This provided a good opportunity to study aeolian–fluvial interaction in the region and for deducing climatic records. From the luminescence dating standpoint these sequences offered a good opportunity for a comparative study of thermoluminescence (TL), blue‐green light stimulated luminescence (BGSL) and infrared light stimulated luminescence (IRSL) on different mineral separates of identical provenance but deposited under different environments. Broadly, within experimental errors, the TL ages agreed with BGSL and IRSL ages on aeolian sands, but differed substantially in the case of fluvially reworked and proximally deposited sands and silts. The sequence provided a record spanning more than 100 ka, with an aeolian phase at > 100 ka, a channel activation phase between 70 and 30 ka and a phase of climate instability between 13 and 8 ka. This appears consistent with the records of monsoon performance during this period, which includes the Younger Dryas. It is also inferred that during the Last Glacial epoch, geomorphological processes in the Thar (both aeolian and fluvial) were dormant largely on account of their relationship with the southwest monsoon. Copyright © 2001 John Wiley & Sons, Ltd.     

Gravel dispersion on a granite pediment (East Mojave Desert,California): a short-term look at erosional processes

Hypotheses about the influence of surface shape, landscape unit and vegetation cover on gravel dispersion were tested on a shallowly dissected portion of a low-sloping granite pediment in the East Mojave Desert of California. Painted gravels (2 to 20 mm diameter) were placed at 117 nodes on a 6m × 3m grid. Gravel movements were recorded after 9.7 cm of precipitation over a four-month period. Vectors indicating the magnitude and direction of gravel movement were longest for summits (24 cm, 34 nodes observed) and shortest for backslopes (14 cm, 27 nodes observed). Gravels beneath shrub canopies were protected significantly from rainsplash transport. To describe dispersion symmetry, eccentricity values were calculated using a ratio of variances of major and minor axes of an ellipse. Mean eccentricity values ranged from about 3 to 250 with dispersion on summits being the most symmetrical and dispersion in washes being the most elongated. Erosion is the most important soil- and pediment-modifying process at upper elevations of the Granite Cove Pediment which is cut off from sediment additions because of washes incised at the base of the mountain front. Copyright © 1999 John Wiley & Sons, Ltd.     

FIELD STUDIES OF SAND PATCH INITIATION PROCESSES ON THE NORTHERN MARGIN OF THE NAMIB SAND SEA

Field studies of protodunes (sand patches) on the northern margin of the Namib Sand Sea suggest that they are initiated in a zone of spatially and temporally fluctuating winds on the distal plinth of one of the south–north linear dunes and migrate northward across granule to gravel substrates. The sand patches disperse as surface roughness increases in the net migration distance. Dispersal of the sand patches is also constrained by sand supply. These studies suggest the importance of interactions between surface and aerodynamic roughness, transport thresholds, and sand supply in the initiation of dunes.     

莫索湾南缘沙漠植物群落多样性抽样方法的研究

2005年9月中下旬,在莫索湾南缘沙漠设置的200m×40m样带内共观测到植物物种22个,其中草本物种占77．3%。通过种一面积方程拟合和临界抽样面积的求解发现要达到抽取群落60%以上物种,临界样方面积至少在518．33m~2以上,而草本物种在735．49m~2以上。样方间相似性指数分析发现样方布样经历的生境异质性越高,物种替代性增加,相似性降低,抽样效率提高。研究发现沿垂直于沙丘走向的方向布样,以4m×4m为基本样方,抽样272m~2即达到60%群落物种,远低于临界抽样面积的求解结果,表明基本样方大小和设置方向对抽样效率产生重要影响。由于沙漠物种偶见种多,频度和密度较低,并且分布的环境特异性强,认为对沙漠植物群落观测,样线法、巢式样方法以及对草本观测的梅花样方法均具有一定局限性,建议对草本和灌木物种多样性观测,在确定合理的布样方向基础上,以4m×4m为基本样方。提出对沙漠植物群落多样性结构和功能有全面了解,必须将局部抽样与区域抽样结合,增加抽样频率和强度。     

草方格固沙带对垄间新月形沙丘形态和移动的影响

为了探讨草方格固沙带对沙丘形态和移动的影响,在塔克拉玛干沙漠腹地的塔中地区,2004年我们在垄间地设置了观测区,对区内新月形沙丘进行了动态测量。数据分析表明,草方格固沙带对垄间低矮新月形沙丘的逆向演变过程和移动扰动很大:在固沙带迎风边缘邻区,沙丘呈正向演变,沙丘移动速度下降;在固沙带内部沙丘呈逆向演变,移动速度加快,而且逆向演变速率大于自然沙面的沙丘。固沙带不能改变沙丘逆向演变的趋势,但从整体上来看,沙丘在固沙带边缘邻区的正向演变延缓了沙丘的逆向演变速率。固沙带对沙丘形态的影响源于削弱近地表风动力、固定沙面使风沙流趋于极度不饱和,而固沙带通过改变沙丘的形态和体积以及地表风沙流的饱和度进而影响沙丘的移动。     

塔克拉玛干沙漠沙垄起伏地形夏季地表温度差异特征

摘 要：开展塔克拉玛干沙漠沙垄起伏地形夏季地表温度观测试验，旨在为塔克拉玛干沙漠环境陆面过程研究提供科学依据。2019年6月7日至9月2日在塔中地区，沿沙垄迎风坡以及背风坡底部、中部、上部、顶点及垄间谷地共设8个地表温度观测点。结果表明：（1）夏季沙垄地表温度最高温出现在垄间谷地，为74.63 ℃，最低温出现在迎风坡底部，为10.52 ℃；地表温度一天中在7:00左右达到最低，15:00左右达到最高。（2）晴天、多云以及浮尘天各观测点地表温度日均变化曲线呈单峰型，降水、扬沙及沙尘暴天呈双峰型；地表温度的最高温与日均值最大值均出现在晴天的垄间谷地，地表温度的最低温及日均值最小值均出现在降水天的迎风坡底部。（3）沙垄顶点与两个底部最大温差范围是顶点与背风坡底部在晴天的温差范围，为0～18.62 ℃，最小温差范围是顶点与迎风坡底部在降水天的温差范围，为0.01～6.18 ℃；迎风坡和背风坡在晴天地表温度温差范围最大，为0.01～16.93 ℃，在降水天温差范围最小，为0.01～4.15 ℃；顶点与两个底部夏季综合温差范围在0～18.62 ℃，迎风坡与背风坡夏季综合温差范围为0～16.93 ℃。塔克拉玛干沙漠地表温度受典型天气影响变化类型多样，沙垄顶点与底部、迎风坡与背风坡地表温度差异受风力及地形作用明显。     

基于结构相似度的巴丹吉林沙漠地表反照率时空分布特征

为研究巴丹吉林沙漠地表反照率的变化规律,以MODIS黑空短波地表反照率数据为基础,利用结构相似度(SSIM)算法,分析巴丹吉林沙漠地表反照率时空分布特征。结果表明:时间尺度上不同沙丘类型地表反照率结构相似度,受到风、降水、地表温度和海拔高度影响均表现为春季最大,秋、夏季次之,冬季最小,但结构相似度值域和变化幅度存在明显差异。在空间上,沙丘数量和间距是巴丹吉林沙漠地表反照率变化的主要影响因素,沙丘数量较多且间距较小时,SSIM值偏小,反之则较大。同时沙丘形态简单或相对稳定会减少地表反照率空间差异性。     

基于Grimm180粒子仪对塔克拉玛干沙漠沙尘暴的定量观测

为了得到沙尘粒子和沙尘质量浓度的实时定量特征,利用Grimm180粒子仪在塔克拉玛干沙漠对沙尘暴进行了实时观测。通过分析Grimm180粒子仪在2018年5月20日和24日两次沙尘暴过程观测的数据得到:在浮尘、扬沙和沙尘暴期间,PM_2.5的质量浓度值随时间变化不大,一般PM_2.5浓度值<1500μg·m^-3,而PM₁₀在不同阶段的变化比较明显,数值在2000~6000μg·m^-3。沙尘粒子谱和沙尘质量浓度谱的分布形状在浮尘、扬沙和沙尘暴基本相同,当粒子直径>0.35μm时,粒子数浓度随直径的增大近似符合M-P分布。从浮尘到扬沙再到沙尘暴,小粒子区(D≤1μm)的占比越来越小,而中粒子区(1μm10μm)的粒子数越来越多并且占比越来越大。当粒子直径为0.35μm左右时,粒子数浓度达到最大值;当粒子直径在25~32μm时,沙尘质量浓度的值最大。在浮尘和扬沙阶段,PM_2.5/PM₁₀>25%;每分钟1 L体积内的沙尘粒子总数大约是4×10⁵,最大沙尘质量浓度<20μg·L^-1。在沙尘暴阶段,PM_2.5/PM₁₀<15%;每分钟1 L体积内的沙尘粒子总数>5×10⁵,最大沙尘质量浓度>25μg·L^-1。这些结论为准确地分析沙尘暴的定量特征提供了科学依据。     

塔克拉玛干沙漠南缘两次极端暴雨的气流模型与水汽输送特征

采用区域自动站逐小时降水观测数据、GPS/MET大气可降水量观测数据和NCEP/NCAR提供的FNL0.25°×0.25°分析数据，通过对比塔克拉玛干沙漠南缘和田地区2次落区接近、强度不同暴雨过程的环流和水汽特征，分析了影响极端暴雨产生的急流和水汽因子特征，结果表明：沙漠南缘暴雨时环流配置符合“三支气流”模型，高空急流、中层偏南风、低层辐合切变的强度与降水量正相关，当高层有极涡直接南伸至中亚发展而成的副热带大槽、中层有气旋前部的强偏南或西南气流、低层有偏东风急流明显西伸与西风急流形成强辐合时有利于出现极端暴雨。沙漠南缘暴雨的水汽源地、输送路径、水汽含量、饱和层厚度与降水量相关，暴雨的水汽源地一般为欧洲和北冰洋，降水区水汽输入以中低层为主，低层比湿大于6 g?kg-1，饱和层位于700 hPa以上；当中高层有来自阿拉伯海、孟加拉湾的由偏南风输送水汽的加入，低层比湿达8 g?kg-1以上、饱和层扩展至750 hPa以下时，可出现极端暴雨。     

基于VOSviewer的塔克拉玛干沙漠沙尘暴研究进展分析

作为中国最大和世界第二大流动沙漠，塔克拉玛干沙漠是我国主要的沙尘暴中心之一，其沙尘天气对当地及周边地区的生产生活会造成巨大影响。利用VOSviewer可视化分析工具，以中国知网（CNKI）数据库和Web of Science核心数据库中塔克拉玛干沙漠沙尘暴相关355篇文献为对象，从发文时间、作者、关键词、期刊来源与学科分布、发文机构（国家）等方面进行可视化与计量分析，进而综述了塔克拉玛干沙漠沙尘暴研究的现状及发展趋势和未来展望。结果表明：塔克拉玛干沙漠沙尘暴研究的中英文文献产出分为2个阶段，即1996—2005年为起步阶段，2006—2020年为稳步发展阶段；塔克拉玛干沙漠沙尘暴的成因、传输特征及发展规律、沙尘暴过程数值模拟预报研究、沙尘天气及沙漠气象等问题受到了国内外众多学者的高度关注；相关论文主要发表在《沙漠与绿洲气象》、《中国沙漠》及Journal of Geophysical Research Atmospheres等期刊，其中《沙漠与绿洲气象》为中文发文量最多的核心期刊，Journal of Geophysical Research Atmospheres为SCI发文量最高的...