不同砾石盖度戈壁床面动力学特征研究

利用野外车载移动式风洞,对莫高窟顶不同砾石盖度戈壁床面的动力学特征进行了实地模拟实验。结果表明：砾石盖度直接决定戈壁床面的粗糙元数量和分布状况,进而影响近地表风速廓线、摩阻速度、床面粗糙度和剪切力;随着风洞进口指示风速的增加,摩阻速度呈线性递增,而动力学粗糙度在波动中呈下降趋势;相同高度,随着砾石盖度的增加,近地表风速逐渐降低,而摩阻速度、动力学粗糙度和剪切力呈线性增加;当床面盖度增加至35%时,动力学粗糙度达到0.30 cm,摩阻速度相应提高到0.93 cm/s,床面剪切力增加至1.11 N/cm。     

三种不同床面近地层湍流输送特征

为了深入理解土壤风蚀发生机制,利用风洞实验风速廓线资料,采用空气动力学方法,计算了干旱、半干旱地区不同类型地表近地层湍流输送随风速以及地表性质的变化特征.结果表明:地表越粗糙,风速越大,湍流输送越强,且湍流输送强度与地面粗糙元密度有关.     

黄土高原风蚀和风水蚀复合区的风蚀气候侵蚀力变化

利用黄土高原风蚀和风水蚀复合区30个气象站1961-2010年的观测资料,根据联合国粮农组织给出的风蚀气候因子指数（C值）的计算公式和线性趋势法、Pettitt变点检测、Morlet小波分析等方法,研究风速的空间分布、时空变化、突变特征和周期特性及其对C值的影响。结果表明：① 该区多年平均风速为2.2 m•s^-1,内蒙古和宁夏境内的部分地区风速较大,陕北、晋西北、陇东和青海部分地区较小。近50 a来风速整体呈显著减小趋势,1970s风速最大,2000s最小。② 年尺度83%的站点风速发生了突变,区域整体突变发生于1982年,四季风速突变时间与年尺度基本一致。③ 近50 a风速存在3次交替变化,1961-1977年和1995-2010年偏大,而1977-1995年偏小,季节尺度上也发现了类似的现象,未来一段时间内该地区风速仍然偏小。④ 该区多年平均C值的空间分布格局和时空变化趋势与风速较为一致,整体也呈现出显著减小趋势。⑤ C值与相对湿度和降水量呈负相关关系,与潜在蒸发量、干旱指数和风速呈正相关关系。风力增强（风速增加）和干旱加剧对于风蚀起到促进作用;温度上升及其造成的蒸发量增大也有助于风蚀的形成。     

基于ITPCAS再分析资料中国近地面风速时空变化特征

准确分析中国近地面风速时空变化规律对区域气候变化、蒸散发的估算、雾霾预报等研究具有重要意义。本文利用1979-2015年ITPCAS再分析资料的近地面风速(10 m)与中国110个气象站点的风速资料,分析该数据集在中国区域的适用性,并对2011-2012年风速数据进行修正,分析该区域近地面风速的时空变化特征。结果表明:①ITPCAS再分析数据集风速资料基本满足应用要求,但部分数据需修正。修正后的风速数据模拟精度得到较大提高,具有较好的应用前景,特别是在西北高寒、干旱地区;②1979-2015年中国62.12%的区域风速为下降趋势,全国平均风速每10 a变化速率为-0. 073 m·s^-1,其中东南诸河流域每10 a变化速率最大(-0.202 m·s^-1);③除珠江流域外,其他各流域风速均呈下降趋势。中国各月平均风速呈单峰形,最大值出现在4月,最小值出现在12月;④年平均风速变化主要表现在3-6月下降速率最大,风速变化趋势在各个流域、各月份保持不变。     

塔克拉玛干沙漠荒漠过渡带空气动力学粗糙度分析

根据塔克拉玛干沙漠北缘荒漠过渡带哈德、肖塘2个试验点的风、温梯度观测数据,利用风速比法计算了中性大气层结、无风沙运动条件的空气动力学粗糙度[WTBX](z0),并分析探讨z0[WTBZ]与下垫面状况、大气稳定度及风速的相互关系。结果表明：哈德、肖塘中性条件下z₀的取值范围分别为 1.81×10^-11～1.20×10^-3m,1.00×10^-11～1.65×10^-3m,平均值为2.70×10^-5m 和6.05×10^-5m,与平坦沙面的值较为接近;z₀随下垫面性质变化明显;空气动力学粗糙度总体上随着理查逊数(R_i)增大而变大,但又呈现出一定的离散程度;空气动力学粗糙度与2 m高度风速呈显著的负指数关系;大气稳定度对空气动力学粗糙度的影响作用有待于进一步确定。      

草原灌木带空气动力学粗糙度研究

为了定量研究灌木带修复退化草原的机理,采用集沙仪和风速廓线仪野外采集了不同高度灌木带及退化草原的风蚀物及风速廓线,利用最小二乘法对风速廓线数据进行计算得到了相应的空气动力学粗糙度。结果表明:灌木带对草地的防护机理在于提升了地表的空气动力学粗糙度,降低了近地表的风速,从而导致灌木带相对退化草原的抗风蚀能力增强,大量风蚀物集中在近地表30 cm范围内;距灌木带的距离越远,空气动力学粗糙度呈现下降趋势;同时对不同高度灌木带的研究发现,0.3 m、0.7 m和1.5 m高的灌木带分别在距背风面3 m、5 m和6 m处的空气动力学粗糙度与退化草原的值趋于一致,此距离为该灌木带的有效防风蚀范围,空气动力学粗糙度及有效防护范围均随灌木高度的增加而增大。     

Effect of stones on the sand saltation threshold during natural sand and dust storms in a stony desert in Tsogt-Ovoo in the Gobi Desert,Mongolia

Non-erodible elements such as stones and vegetation are key to controlling wind erosion and dust emission in drylands. Stony deserts are widely distributed in the Gobi Desert, but the effect of stones on wind erosion and dust emission have not been well studied, except under artificial conditions. In this study, we evaluated the effect of stones on wind erosion and dust emission by measuring the sand saltation threshold in a stony desert in Tsogt-Ovoo in the Gobi Desert, Mongolia, under natural surface conditions during sand and dust storms. We quantified the amount of stones by measuring the roughness density, and determined the threshold friction velocity for sand saltation by measuring wind speed and sand saltation count. Our results showed that the threshold friction velocity increased with the roughness density of stones. In the northern part of the study area, where neither a surface crust nor vegetation was observed, the roughness density of stones was 0.000 in a topographic depression (TD), 0.050 on a northern slope (N.SL), and 0.160 on the northern mountain (N.MT). The mean threshold friction velocity values were 0.23, 0.41, and 0.57 m/s at the TD, N.SL, and N.MT sites, respectively. In the southern part of the study area, the roughness density values of stones were 0.000 and 0.070-0.320 at the TD and southern slope sites, respectively, and the mean threshold friction velocities were 0.23 and 0.45-0.71 m/s, respectively. We further compared the observed threshold friction velocities with simulated threshold friction velocities using Raupach's theoretical roughness correction and the measured roughness density values, and found that Raupach's roughness correction worked very well in the simulation of threshold friction velocity in the stony desert. This means that the results of our stone measurement can be applied to a numerical dust model.     

Wind tunnel test on the effect of metal net fences on sand flux in a Gobi Desert,China

The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions: no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m(i.e., 13 H, where H denotes the fence height) downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.     

1971-2010年东北三省平均地面风速变化

利用1971-2010年逐月观测资料,分析东北三省年、季节和月平均地面风速变化的时空特征。结果表明：① 东北三省年平均地面风速变化呈显著递减趋势,变化速率为-0.23 m·s^-1·(10 a）^-1,1971-2000年（前30 a）、1981-2010年（近30 a）和1991-2010年（近20 a）平均地面风速变化均呈显著递减趋势,线性变化速率分别达-0.25 m·s^-1·（10 a）^-1、-0.20 m·s^-1_·（10 a）^-1和-0.17 m·s^-1_`（10 a）^-1,均通过了0.001显著性检验;② 近40 a东北三省各季和逐月平均地面风速变化趋势呈显著递减趋势,均通过了0.001显著性检验;春季递减速率最大,冬、秋季次之,夏季最小;③ 近40 a东北三省地面年平均风速的趋势变化除个别站点外,其他均呈现出比较一致的显著递减趋势,但最近20 a呈显著递减趋势的站点数在减少,递增趋势的站点数增多。     

浑善达克沙地南缘风蚀量的研究

在对浑善达克沙地南缘多伦县沙漠化土地调查中,就其风蚀地貌进行了详细的研究,不仅论证了风蚀地貌的形成、类型和分布,而且实测了不同类型区的风蚀量数据。并采用克拉瓦洛维克的风蚀强度公式计算了该地区风蚀量的理论值。以测定数据为基础,研讨了增加地表粗糙度的方法及防止或减缓风蚀的有效途径,并且具有在同类地区示范推广作用。     

Effect of flexible and rigid roughness elements on aeolian sand transport

In developing countermeasures to reduce the negative effects of strong dust events, the fundamental relationship between surface conditions and sand transport remains problematic. We conducted field observations and wind tunnel experiments to examine the effect on sand transport efficiency of actual frontal area when using flexible roughness elements (artificial grass) and rigid roughness elements (tufts of stiff wire). In the field observations, the sand trap ratio approached a limit as the frontal area of artificial grass, measured as the Actual Frontal Area Index (AFAI), approached 25%, equivalent to a vegetation cover of 20%. The wind tunnel experiments showed that the height of deposited sediment decreased downwind with both roughness elements, due to their reduction of both shear velocity and sand transport rates. The sediment flux decreased as the AFAI increased, and the rigid roughness element trapped more sand particles than the flexible one except at higher wind speeds and lower AFAI values. The sand trapping efficiency was greater for rigid roughness elements than for flexible ones, probably due to their high aerodynamic resistance, and thus wire tufts were more effective for trapping sand than artificial grass at higher AFAI values.     

戈壁、流沙地表风沙流特性研究

通过对戈壁、流沙地表风沙流特性的风洞模拟实验研究,风沙流中的风速廓线分布满足幂函数的形式,其幂指数在0.20左右。对于戈壁地表,在不同风速下,相同高度层含沙量具有很大的相关性,风沙活动层主要集中在距地表20cm范围内;由于沙粒与戈壁地表的砾石发生碰撞,风沙流不再服从对数关系递减,其极值出现的高度随风速的增加而上移,呈现"象鼻效应"。     

沙漠地区风沙活动特征——以中国科学院风沙观测场为例

运用中国科学院风沙科学观测场的实测资料,对腾格里沙漠风沙环境特征进行初步分析,内容包括起沙风、风沙活动强度、风沙流结构和沙漠边界层的风速廓线.该地区的起沙风以6～8 m/s为主,占总起沙风的71.63%,其次为8～10 m/s,占19.24%,两者之和占90.87%;大风日数为4天;风向以W-N组风向为主;占全年的53.14%.年输沙势为36.56VU,风能属于低风能环境,单一主风向和单风态风环境.风沙流主要集中在地表的0.1 m,占总输沙量的95.46%.观测场近地层厚度大于50 m.     

甘肃省风速变化趋势分析

近年来,我国风能资源开发增长迅速,甘肃省风能资源储量在全国名列前茅。为降低风电企业投资的风险,需要对当地多年的风速状况进行评估。文中选用甘肃省79个台站1976年至2010年35年的风速资料,30个台站的历史沿革资料,采用T检验法、SNHT(Standard Normal Homogeneity Test)方法及经验正交分解方法(EOF)对甘肃省风速资料进行分析。T检验表明,甘肃省79个站35年的风速资料有3.98%的存在非均一性;资料分析结果表明,甘肃各地风速除陇中及定西部分地区略有上升外,大部分地区风速呈下降趋势,包括风能资源丰富的地区,且下降趋势较明显,其中河西祁连山区风速下降在0.13m/s.10a～0.26m/s.10a之间,河西东部地形平坦区域风速下降在0.13m/s.10a以下;陇南及陇东大部分地区风速下降在0.13m/s.10a以下。甘肃台站风速每十年变化量与本站1976～2010年平均风速比较结果显示:除陇中及定西部分地区风速略有上升,每十年上升在5%～10%之间外,河西祁连山区风速每十年下降在5%～15%之间,河西东部地形平坦区域风速每十年下降在5%以下;陇南及陇东大部分地区风速每十年下降在5%～10%之间。这是今后风电场投资必须要考虑与防范的风险因素之一。     

新疆策勒绿洲-沙漠过渡带风、温、湿相关性分析

为研究绿洲与沙漠间水、气、热量运移规律,运用统计法、相关分析法等,选取策勒绿洲-沙漠过渡带4个不同下垫面风速(V)、气温(T)、大气相对湿度(RH)、光合有效辐射(PAR)、太阳辐射(SR)等气象要素进行相关性分析。结果表明:一天当中,起沙风发生在14:00—16:00的频率最大,且从早到晚呈现先上升再下降的趋势,与气温的日变化趋势基本一致。一年中,流沙地月平均风速与月平均气温的变化同步。从流沙地到绿洲内部,月平均风速的变化趋势明显减弱,气温的减弱趋势较小,大气相对湿度有一定增加的趋势。流沙地的月平均风速、温度呈较好的正相关性,一天中0.5 m与2 m高度之间气温、湿度差的负相关性较好。在6种天气类型中,4个下垫面每2个气象要素之间都在0.01水平上呈显著相关,阴雨天不同高度的风速与部分气象要素之间相关性不显著,流沙地在扬沙天气下、半固定沙地在浮沉天气下、固定沙地在阴雨天天气下,0.5 m高度的风速和PAR、SR均不呈显著相关性。     

Comparison of wind tunnel and field experiments to measure potential deposition of fenpropimorph following volatilisation from treated crops

The potential for short-range transport via air, i.e. volatilisation from the area of application and subsequent deposition on adjacent non-target areas, was investigated for the fungicide fenpropimorph in a wind tunnel system and under outdoor conditions in a higher-tier field study. Fenpropimorph 750 g L(-1) EC was applied post-emergence to cereal along with a reference standard lindane EC. Stainless steel containers of water were placed at different distances downwind of the application area to trap volatile residues during a study period of 24 h following application. Meteorological conditions in the wind tunnel as well as on the field were constantly monitored during the study period. The wind tunnel system was a partly standardised system on a semi-field scale, i.e. wind direction and wind speed (2 m s(-1)) were constant, but temperature and humidity varied according to the conditions outside. In the field experiment, the average wind speed over the 24 h study period was 3 m s(-1) and no rainfall occurred. Three different measuring lines were installed on the non-target area beside the treated field to cover potential variations in the wind direction. However, no significant differences were observed since the wind direction was generally constant. Fenpropimorph was detected in minor amounts of 0.01-0.05% of the applied material in the wind tunnel experiment. Even at a distance of 1 m beside the treated field, no significant deposition occurred (0.04% of applied material after 24 h). In the field, less than 0.1% of the applied fenpropimorph was detected at 0 m directly beside the treated field. At 5 m distance the deposition values were below 0.04%, and at 20 m distance about 0.01%. In general, the amounts of deposited fenpropimorph detected in the partly standardised wind tunnel system and the higher-tier field study were in good agreement.     

塔克拉玛干沙漠腹地沙尘天气特征

利用塔克拉玛干沙漠腹地塔中气象站2007—2011年的地面(10 m)风速、风向和沙尘天气等气象要素,分析沙漠腹地的沙尘天气特征。结果表明:1塔克拉玛干沙漠腹地沙尘频率和强风频率年、月分布具有较好的一致性,沙尘天气具有明显的季节性,春、夏季占全部沙尘频次的88.3%,冬季仅占总数的2.3%。2春、夏季沙尘天气的高发时段为12:00—00:00;20:00发生频次最多,分别占春、夏季沙尘频次的12.7%和10.8%,秋季和冬季沙尘天气高发时段为14:00—21:00。3出现沙尘天气时,风向主要集中在E、ENE、N和NNE 4个方向。4沙漠腹地临界起沙风速ut5%为4~5 m·s-1,一般地表的临界起沙风速ut50%为5~6 m·s-1;5从NfDO分布来看,春、夏两季要明显高于秋冬季节,其中4月最大,为0.284。因此,沙漠腹地春、夏季易发生沙尘天气。     

Wind regimes and associated sand dune types in the hinterland of the Badain Jaran Desert,China

Wind controls the formation and development of sand dunes. Therefore, understanding the wind regimes is necessary in sand dune research. In this study, we combined the wind data from 2017 to 2019 at four meteorological stations (Cherigele and Wuertabulage stations in the lake basins, and Yikeri and Sumujilin stations on the top of sand dunes) in the hinterland of the Badain Jaran Desert in China, with high resolution Google Earth images to analyze the correlation between the wind energy environments and dune morphology. The results of data analysis indicated that both the wind direction and sand drift intensity exhibited notable spatial and temporal variations. The highest level of wind activity was observed in spring. Northwesterly and northeasterly winds were the dominant in the Badain Jaran Desert. At the Cherigele, Wuertabulage, and Yikeri stations, the drift potential (DP) was below 200.00 vector units (VU). The wind energy environments in most areas could be classified as low-energy environments. The resultant drift direction differed at different stations and in different seasons, but the overall direction was mainly the southeast. The resultant drift potential (RDP)/DP ratio was greater than 0.30 in most parts of the study area, suggesting that the wind regimes mainly exhibited unimodal or bimodal characteristics. Differences between the thermodynamic properties and the unique landscape settings of lakes and sand dunes could alter the local circulation and intensify the complexity of the wind regimes. The wind regimes were weaker in the lake basins than on the top of sand dunes. Transverse dunes were the most dominant types of sand dunes in the study area, and the wind regimes at most stations were consistent with sand dune types. Wind was thus the main dynamic factor affecting the formation of sand dunes in the Badain Jaran Desert BJD. The results of this study are important for understanding the relationship between the wind regimes and aeolian landforms of the dune field in the deserts.     

东亚北风异常对西北东部春季降水的影响

利用1961-2008年NCEP/NCAR(2．5°×2．5°)再分析逐月500 hPa高度场资料和1961-2008年西北地区东部陕、甘、宁、青4省170个气象观测站的月降水量资料,计算春季东亚北风指数,分析研究区春季降水的历史演变规律、东亚北风指数的年代际变化及其与西北春季降水的关联。结果表明:50 a来降水演变特点是以黄河为界,黄河以西降水呈增多趋势,黄河以东降水呈减少趋势,降水减少的幅度明显大于增加的幅度;特别是近20 a,黄河以东广大区域降水减少的幅度越来越大,干旱化趋势明显,而青海南部、河西走廊则降水呈增加趋势。在此期间,春季东亚北风逐渐增强,特别是20世纪90年代中期以后明显增强。进一步分析表明,当春季东亚北风偏强（弱）时,除青海南部外,西北地区东部大部分地方降水偏少（多）,即春季东亚北风异常增强,可引起西北地区东部黄河以东干旱少雨,导致干旱化加剧。     

农田耕作方式与土壤风蚀强度关系的风洞模拟实验

以土壤风蚀严重的河北坝上康保县为研究区,采用风洞试验的技术手段,对农田耕作方式与土壤风蚀强度的关系进行研究。结果表明,农田留茬与翻耕、农田垄向及农作物残茬高度的差异对土壤风蚀强度有较大影响。垄向平行主风向的风蚀强度大于垄向垂直主风向的风蚀强度。风速越大,垄向不同造成的风蚀强度的差异越大,尤其是当风速≥15m/s时,风蚀强度的差异表现得较为明显;风蚀强度与留茬高度呈负相关;翻耕地的风蚀强度大于任何留茬地的风蚀强度;风蚀强度与风速变化呈现出指数函数变化规律。因此,农田垄向垂直主风向、作物收获后不进行翻耕、留有适度茬高、优先种植残茬硬度较大的莜麦作物,这样的耕作方式可有效降低土壤风蚀强度,缓解河北坝上地区农田土壤风蚀状况。