青藏高原地区对流层顶的时空变化特征

利用欧洲中期天气预报中心(ECMWF)提供的ERA-Interim再分析资料,分析1980-2010年青藏高原地区对流层顶的时空分布特征.结果表明:①青藏高原及周边地区对流层顶等压线基本呈纬向分布,对流层顶的高度随着纬度的增加而降低.对流层顶等压线梯度有明显的南北变化,北部的梯度值较大,南部较小;②青藏高原地区对流层顶的高度有明显的季节变化,其平均气压值在夏季最低,冬季最高,这可能与温度的高低和对流活动的强弱有关;③不同季节对流层顶的高度还存在着不同的年(代)际变化,其中秋季和冬季的振荡上升趋势较大,春季和夏季的振荡上升趋势较小;④青藏高原地区对流层顶存在明显的周期变化,不同季节对流层顶存在着不同的周期变化.其中,年平均的对流层顶变化周期为3 a和11a,春季对流层顶的变化周期为5 a,夏季对流层顶的变化周期为2 a和9 a,秋季对流层顶的变化周期为3 a和11a,冬季对流层顶的变化周期为6a和11a.     

格尔木地面、低空风场特征分析

利用格尔木地面和探空风速、风向资料,对格尔木风场特征进行分析。得出各季平均风速的日变化较为明显;年内各月之间平均风速变幅不大;大气边界层风速随高度增加而增大;低空风速的垂直变化一日中只有07时平均风速基本上随高度增加而稍有增大。格尔木常年以西风为主导风向,其次是西西北风和南西南风,各风向下的平均风速玫瑰图春、夏、秋、冬及年很相似,均以偏西风最大,偏东风次之。格尔木常年以w为主导风向,其次是wws风和sws。日变化中10～17时为一日中较大时段,20～23时为一日中较小时段。小于1.5m/s和1.5～3.0m/s的风速频率高,风速较大有利污染物的扩散。     

民勤地区沙尘暴近地面风速特征及其与环境因子的关系

作为沙尘暴发生必不可少的动力条件,风是判定沙尘暴强度的主要指标,也是沙尘暴预测预报的依据。虽然人类对风的认识很早、研究很多,但是对沙尘暴过程中的风速特征仍然在不断的探索中。文中研究了民勤荒漠区、绿洲边缘和绿洲内部三种下垫面近地面50m沙尘暴风速特征及其与环境因子的关系。主要研究结果是:1)在三种不同的下垫面条件下,沙尘暴风速在近地面50m范围内风速均随高度遵循幂函数关系递增。2)从荒漠区到绿洲边缘近地表0-50m内风速平均削减4.11%,再从绿洲边缘到达绿洲内部风速平均削减30.45%。风穿越研究断面,随高度增加风速削减率逐渐减小。3)不同季节,沙尘暴平均风速没有明显差异,但地表粗糙度越小沙尘暴平均风速的季节性差异越大,高度越高季节差异越大。4)绿洲内部地表粗糙度为2.121 cm,绿洲边缘为0.082 cm,荒漠区为0.023 cm。5)根据每次沙尘暴过程中30m in平均风速随时间的振荡曲线的轮廓可将沙尘暴归纳为三类,分别为单峰型、双峰型和多峰型。这三种不同类型的沙尘暴在大气环流背景、沙尘暴的发生时间、沙尘暴过程中风速的时空变化等均有明显的不同。在一次沙尘暴过程中,从垂直梯度看,随着高度的增加风速随时间曲线的振幅增大,而振荡频率降低;从水平梯度看,沙尘暴流场从荒漠区经绿洲边缘到达绿洲内部,风速曲线振幅逐渐减小,振荡频率逐渐增加。     

新疆策勒4个典型下垫面近地层风速脉动特征

以塔克拉玛干沙漠南缘策勒沙漠-绿洲过渡带为研究区,对流沙地、半固定沙地、固定沙地和绿洲内部4个下垫面平均风速、风速脉动和风向脉动特征进行分析,探讨风速、风向脉动差异原因。结果表明:1平均风速与阵风风速之间符合线性相关性,相关性随着距离地表高度的增大而增大,各高度平均风速与阵风风速都呈极显著正相关(P0.01);2从流沙前缘沿主风向至绿洲内部,随着植被盖度的增加,平均风速逐渐降低,且离地表越近降低的幅度越大;3随距离地表高度的增大,各测点风速脉动强度呈现先增大后减小的趋势,风速脉动相对值呈减小的趋势。从流沙地、半固定沙地、固定沙地到绿洲内部,风速脉动强度和风速脉动相对值总体上呈现增大的趋势,而在4个下垫面中,绿洲内部不同高度的风速脉动强度在夏季表现为最小,在冬季表现为最大;4风向脉动幅度以流沙地最小,半固定沙地、固定沙地次之,绿洲内部最大,即随植被覆盖度增加而增大。     

毛乌素沙地风沙流结构的研究

运用曲线拟合、拟合方程等方法,对毛乌素沙地南缘流动沙丘0～30cm垂直高度范围内的风沙流结构进行了分析研究。结果表明:在0～30cm高度,输沙率均与风速成正比,与高度成反比,幂函数拟合关系最佳。其中,各高度层输沙率随风速的变化分别呈幂函数或指数函数关系,同风速下输沙率随着高度的增加而减小,呈幂函数或指数函数关系;随着风速和气流中总输沙率的增加,0～30cm高度范围内的绝对输沙率增加,相对输沙率(%)的变化为下层趋于减少,中层略变,上层增加,风沙流结构的特征值λ增大;风沙流中沙粒粒度沿垂向变化为细沙增加,中沙减少,沙粒平均粒径变细。     

风速对海岸沙丘表面风沙流结构影响的实证研究

在河北昌黎黄金海岸形态典型的横向沙脊顶部,对不同风速下的风沙流结构进行了观测。结果表明:随着风速的增加,风沙流中40 cm高度内的绝对输沙量增加,40~60 cm高度内各层的绝对输沙量减少;相对输沙量,在0~4 cm高度内减少,4~20 cm高度内增加,20~44 cm高度内变化较小,44~60 cm高度内减少;风沙流结构模式在0~40 cm高程内为指数分布,但在0~60 cm高程内随风速增大由幂函数分布转变为指数函数分布,在40~60 cm高程内则转变为相关性更强的多项式函数分布。风速变化对风沙流结构的上述影响,主要与随风速增加增大了沙粒的搬运高度以及气流搬运沙物质的粒度组成有关。     

内蒙古高原小叶锦鸡儿灌丛沙堆对气流结构与风蚀的影响

小叶锦鸡儿(Caragana microphylla)灌丛沙堆是内蒙古高原东南部农牧交错区的主要风沙堆积类型。通过对该区典型灌丛沙堆周围风沙气流的野外观测,结果表明,气流方向与强度和输沙率,随沙堆不同位置而发生变化。绕过沙堆两侧的气流和越过沙堆上部的气流在背风侧汇集,并在同等沙堆高度的范围内和1.5倍沙堆高度的水平范围内出现涡流。从灌丛沙堆迎风坡脚经南北两侧至背风坡脚以及背风侧5倍沙堆高度的水平距离间,风速依次出现逐渐增大—最大—逐渐减小—最小—回増至旷野风速的变化过程。在不同风向条件下,灌丛沙堆背风侧气流的风速廓线,并不完全遵循对数变化规律,沙堆南侧气流在0.3~0.6 m高度处出现变异。另外,沙堆周围输沙率在迎风侧和南北两侧与风速变化基本一致,但在背风侧因气流方向紊乱而出现变异。输沙率随高度增加,在沙堆迎风侧至两侧各部位呈有规律递减,但在背风侧无规律。     

残茬高度对土壤风蚀量影响的试验研究

在内蒙古自治区武川县建立农田土壤风蚀试验区,采用内蒙古农业大学研制的移动式风蚀风洞和旋风分离式集沙仪,观测不同残茬高度条件下农田土壤的风蚀情况.试验结果表明:土壤风蚀量和扬起沙尘的高度随风速的增加而增加,随着作物秸秆残茬高度的增加而降低,且风蚀量与高度变化符合指数函数关系,土壤颗粒主要集中在近地表层内运动.保护性耕作可明显地提高起沙风速,减少农田土壤损失,当秸秆高度为30 cm时,风蚀量仅为传统耕地的1/4左右.     

土壤风蚀量随残茬高度的变化规律研究

在内蒙古自治区武川县建立农田土壤风蚀试验区,采用内蒙古农业大学研制的移动式风蚀风洞和旋风分离式集沙仪,直接在农田上观测不同残茬高度条件下的农田风蚀土壤损失情况。试验结果表明:土壤风蚀量和扬起沙尘的高度随风速的增加而增加,随着作物秸秆残茬高度的增加而降低,且输沙量与高度变化符合指数函数关系,土壤颗粒主要集中在近地表层内运动。保护性耕作可明显地提高启沙风速,减少农田土壤损失,当秸秆高度为30 cm时,风蚀量仅为传统耕地的1/4左右。     

基于SPH方法的风沙流运动特性研究

文中基于光滑粒子流体动力学(Smoothed Particle Hydrodynamics:SPH)方法,采用五次样条光滑函数,通过调节不同类型粒子光滑因子,对风沙流运动特性进行分析:1)在风沙流起动阶段,沙粒平均水平速度随高度增加而增大,同一高度处沙粒平均水平速度随时间推移而减小。2)风沙流稳定前后,沙粒数均随高度的增加而减少。3)风沙流形成过程中气体粒子在计算域中心位置产生涡流,并随着时间推移,涡流又出现在计算域中上及右下方位置。4)起沙前后气体脉动强度随摩阻风速增加而增加,随高度增加呈现不同变化。结果表明:该方法模拟精度较高,适用于解决风沙两相流数值模拟问题。     

行带式柠条林合理带间距的研究

该文以和林格尔县的行带式柠条林为研究对象,采用十路风向风速自动采集仪,在无叶期选择上风方向的三条连续完整行带式柠条林和第二条出现有3m缺口状况的风速分别进行观测,进而分析了行带式柠条林的防风效益以及缺口对其防风效果的影响,并以此为依据讨论了林带间距的适宜宽度。结果表明:行带式柠条林的带间距至少可拉大到20m。     

土壤风蚀的野外风洞实验研究

<正> 土地的不断沙漠化已给自然的生产潜力和人类的生活环境带来了巨大的危害,目前这种危害正在加速地强化着。因此作为沙漠化研究中的一个重要内容——土壤风蚀的研究就显得十分重要了。我们内蒙古林学院在国内外专家的帮助下,于1986年初,顺利地     

中哈边境迁飞蝗虫降落的天气过程分析——以1999年塔城地区为例

为明确中哈边境迁飞蝗虫降落过程的气象背景,选择中哈边境塔城地区蝗虫迁飞为害最严重的1999年为例,基于当年迁飞蝗虫降落时间、地点及为害程度等数据,利用中尺度气象预报与研究(weather research and forecasting,WRF)模式模拟塔城地区迁飞蝗虫降落的天气变化。结果表明,垂直速度达到0.22 m/s的下沉气流、风速为3 m/s以上的东南风向、降雨和低于19℃的温度胁迫是影响1999年7月10日中哈边境迁飞蝗虫降落的主要气象因素;统计当年迁入蝗虫降落事件,发现下沉气流、风向切变、降雨和低温在蝗虫降落过程中出现的频次占总迁入蝗虫降落事件的70%、50%、30%和10%,其中下沉气流和风向切变是影响蝗虫降落的主导因子。表明利用WRF模式可准确预测迁飞蝗虫跨境为害降落区域的天气过程。     

Effects of wind guide plates on wind velocity acceleration and dune leveling: a case study in Ulan Buh Desert,China

The areas used to be covered by shifting sand dunes have been reclaimed rapidly in recent years. However, it is a challenge to reclaim high sand dunes because it is rather costly to level the high dunes to gentle arable lands. In this study, a wind guide plate was used to change the characteristics of natural wind to level the sand dunes. The use of wind energy could significantly increase the efficiency of dune leveling and decrease the cost. Low wind velocity is a typical characteristic in Ulan Buh Desert of China where the average wind speed is much lower than the threshold velocity for sand movement. The experiment of this study was conducted to accelerate the wind velocity by a wind guide plate to level a sand dune. Results show that the threshold velocity for sand movement is 3.32 m/s at 10 cm above the sand surface in Ulan Buh Desert. A wind guide plate set at an angle less than 50° could significantly increase the wind velocity. The wind velocity could be accelerated up to the threshold velocity for sand movement behind a plate when the plate is at the angles of 20°, 25°, 35° and 40°. The most significant acceleration of wind velocity appears at 1.5 and 3.0 m behind the plate with an angle of 25°. An obvious wind velocity acceleration zone exists behind the wind guide plate when the angles are at 25°, 35°, 40° and 45°, with the most obvious zone under the angle of 45°. The results also show that the total amount of sand transferred over the experimental period increased by 6.1% under the effects of wind guide plates compared to the sand moved without wind guide plates. The results of the study will provide theoretical and practical supports for desert management in sand dune areas.     

Changes in wind activity from 1957 to 2011 and their possible influence on aeolian desertification in northern China

Wind activity is proved to have significant impacts on aeolian desertification. Clarifying the fluctuations and change trend of wind velocity is important for understanding their influence on aeolian desertification. In this study, we used a dataset of wind velocities collected from 93 meteorological stations across northern China from 1957 to 2011 to analyze the changes in wind activity during this period. We tested the monotonic and step(abrupt) trends for annual and seasonal data of mean wind velocity by using Mann-Kendall and Mann-Whitney tests, respectively. The results indicated that the annual mean wind velocity decreased by 0.83 m/s from 1957 to 2011. The decreasing trends were also significant(P<0.01) for each season. The magnitude of the decrease was smallest in the east of northern China and largest in the west of northern China, and the most remarkable decrease occurred in the northwest of northern China. Abrupt decreases in annual and seasonal mean wind velocities occurred in the mid-1980 s, which was consistent with the changes in aeolian desertification since the mid-1980 s in northern China. As revealed by our study, although both modern aeolian desertification and ecosystem rehabilitation are affected by human activities to some extent, they are also likely to be strongly controlled by climate change, especially by wind activity.     

灌木林优化配置格局对土壤风蚀的影响

低覆盖度时,灌木林的水平配置格局成为制约土壤风蚀的重要因素。以宁夏盐池县风沙区人工灌木林基地为试验区,研究了不同下垫面类型和不同配置格局的灌木沙障对风速、近地表输沙率和地表粗糙度的影响。结果表明:灌木林的防治土壤风蚀能力与灌木林的种类、高度和配置格局有直接关系:行带式配置能显著提高灌木林的防风效果,其中以沙柳林效果最佳;三行一带、平均高1.5m、行距1.5m、插深0.5m配置规格的沙柳沙障对地表土壤风蚀的控制效果最好,但防护范围限15倍带高以内;在行数一定的情况下,沙障高度越低,控制土壤风蚀能力越强。     

乌鲁木齐市近43年风速气候特征分析

利用乌鲁木齐市1961-2003年逐日平均风速资料,分析了乌鲁木齐市近43年风速的基本气候特征、变化趋势和年际、年代际变化等。其主要结果是:乌鲁木齐市年平均风速为2.47m.s-1。一年四季中夏季的平均风速最大为3.08m.s-1,冬季最小为1.52m.s-1,春季和秋季则分别为2.94m.s-1和2.31m.s-1。近43年乌鲁木齐市春季、夏季、秋季、以及年风速呈下降趋势,而冬季呈上升趋势。Morlet小波分析表明乌鲁木齐市风速变化具有准6、8年的年际尺度和准13、21年的年代际尺度周期变化,其中准13年周期振荡最为强烈。乌鲁木齐市风速变化是不同尺度周期振荡综合作用的结果。     

Effects of variability in landscape types on the microclimate across a desert–oasis region on the southern margins of the Tarim Basin,China

Microclimates play important roles in controlling water budgets and water vapor transportation, as well as vegetation growth characteristics. In order to understand the differences in meteorological parameters under different vegetation cover (VC) and terrain conditions, wind velocity, air temperature, relative humidity (RH), photosynthetically active radiation (PAR), and solar radiation were simultaneously monitored on shifting, semi-fixed and fixed sandy lands, and an oasis. The air temperature and RH differences among the four landscape types were obvious in the period from May to October. It was found that the higher elevations of semi-fixed sandy land can influence PAR and solar radiation during sand-blowing weather. The differences of air temperature and RH among the four sites during the dust-storm and rainy days were not obvious, but their differences during sand-blowing weather were greater than during rainy weather and less than during floating-dust and sunny weather. The differences of PAR and solar radiation among the four landscape types were most obvious during the dust-storm event. During most of the weather types studied, significant positive correlations were found between wind velocity and temperature, PAR, and solar radiation, as well as between temperature and PAR, and solar radiation. Meanwhile, significant negative correlations were found between RH and wind velocity, temperature, PAR, and solar radiation. VC and topography were found to be the main factors influencing the changes in meteorological parameters between desert–oasis ecotone and oasis.     

Attribution analysis and multi-scenario prediction of NDVI drivers in the Xilin Gol grassland,China

Grassland degradation is influenced by climate change and human activities, and has become a major obstacle for the development of arid and semi-arid areas, posing a series of environmental and socio-economic problems. An in-depth understanding of the inner relations among grassland vegetation dynamics, climate change, and human activities is therefore greatly significant for understanding the variation in regional environmental conditions and predicting future developmental trends. Based on MODIS (moderate resolution imaging spectroradiometer) NDVI (normalized difference vegetation index) data from 2000 to 2020, our objective is to investigate the spatiotemporal changes of NDVI in the Xilin Gol grassland, Inner Mongolia Autonomous Region, China. Combined with 12 natural factors and human activity factors in the same period, the dominant driving factors and their interactions were identified by using the geographic detector model, and multiple scenarios were also simulated to forecast the possible paths of future NDVI changes in this area. The results showed that: (1) in the past 21 a, vegetation cover in the Xilin Gol grassland exhibited an overall increasing trend, and the vegetation restoration (84.53%) area surpassed vegetation degradation area (7.43%); (2) precipitation, wind velocity, and livestock number were the dominant factors affecting NDVI (the explanatory power of these factors exceeded 0.4). The interaction between average annual wind velocity and average annual precipitation, and between average annual precipitation and livestock number greatly affected NDVI changes (the explanatory power of these factors exceeded 0.7). Moreover, the impact of climate change on NDVI was more significant than human activities; and (3) scenario analysis indicated that NDVI in the Xinlin Gol grassland increased under the scenarios of reduced wind velocity, increased precipitation, and ecological protection. In contrast, vegetation coverage restoration in this area was significantly reduced under the scenarios of unfavorable climate conditions and excessive human activities. This study provides a scientific basis for future vegetation restoration and management, ecological environmental construction, and sustainable natural resource utilization in this area.