共查询到19条相似文献，搜索用时 234 毫秒
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利用塔克拉玛干沙漠北缘肖塘地区涡动相关系统三维方向风速（u，v，w）、气温、CO2、H2O等观测数据，分析了夏季典型晴天不同大气稳定度条件下湍流功率谱和协谱。结果表明：大部分情况下湍流速度谱分布满足-2/3幂指数率，垂直方向高频段惯性副区符合程度更高，水平方向次之；CO2和H2O浓度则符合程度较低；温度谱与无因次频率总体上都具有很好的相关性。垂直风速与径向风速u的协谱斜率拟合值大多数情况下更接近-1，而在近中性层结条件下更符合-4/5斜线。稳定层结条件下的协谱峰值比不稳定层结时更大，且约大一个量级；不稳定层结条件下高频段协谱近直线型下降。u谱对应的谱峰波长随稳定度增加而减小，v谱和T谱对应的谱峰波长随稳定度的增加没有规律性增减；u、v、w、T谱谱峰波长约67~827、69~2417、4~54、12~661 m。 相似文献
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塔克拉玛干沙漠腹地近地层湍流能谱特征分析 总被引：1，自引：1，他引：0
利用塔克拉玛干沙漠腹地近地层湍流观测资料,计算并分析了不同稳定层结条件的湍流速度谱、温度谱及局地各向同性特征。结果表明,湍流速度谱和温度谱在惯性副区均满足Kolmogorov的-2/3指数规律,且稳定条件的相关系数更高;速度谱满足湍流各向同性的低频限制理论。近中性条件的温度谱和弱不稳定条件的速度谱在高频段有尾部上翘现象;稳定情况下的v谱和近中性条件的u谱、T谱在低频处也有上翘现象。沙漠腹地水平湍流尺度范围介于森林和草地之间,不稳定层结比稳定层结的谱峰更偏向低频端,且峰值尺度更大。 相似文献
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利用塔中气象站垂直探测系统的湍流观测资料,计算并分析了塔克拉玛干沙漠腹地不同稳定层结条件的湍涡特征长度尺度、能量耗散率及湍流结构函数参数特征。结果表明：湍涡特征长度尺度在弱不稳定或近中性条件时最大,随不稳定程度的增强有明显减小的趋势,随着稳定程度的增加有先迅速减小后又缓慢增加的趋势,且热量特征长度尺度比动量特征长度尺度总体要大一个数量级;无因次湍流热量耗散率的拟合函数形式与其他试验一致,但经验系数略有差异;利用Kaimal公式和湍流谱方法间接计算的稳定条件湍流能量耗散率及湍流结构函数参数具有较好的一致性。 相似文献
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内蒙古奈曼流动沙丘下垫面近地面能量收支研究 总被引：4，自引：0，他引：4
利用2000年7月18日~8月12日在内蒙古奈曼流动沙丘下垫面取得的大气边界层观测资料,分析了地表能量收支各项的日变化、总体输送系数日变化及其与稳定度的关系;比较了涡旋相关法、波文比-能量平衡法所得到的感热通量。得到奈曼流动沙丘下垫面平均地面阻曳系数Cd为4.69×10-3;感热通量总体输送系数Ch为2.25×10-3。在近中性层结条件下,Cd和Ch分别为4.83×10-3和1.34×10-3。近地面层湍流方差在不稳定层结下均满足Monin-Obukhov相似理论。 相似文献
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为评估忽略大气稳定性对潜在蒸散发(Potential Evapotranspiration,PET)估算的影响,本文以亚热带森林下垫面为例,结合涡动相关观测及莫宁-奥布霍夫相似原理,探讨了冠层上方大气层结变化规律,比较了基于中性假设和考虑大气稳定性影响的PET之间的差异。结果表明：①中性、稳定和不稳定3种大气层结具有明显的日内与季节变化特征,不稳定层结在中午居多,稳定层结在早晨和傍晚居多,而中性层结在昼间均有分布;同时,春夏两季的不稳定层结高频时段较长,而秋冬两季相对较短;总体上,观测期内不稳定、中性和稳定3种层结平均占比分别为41.4%、34.7%与24.0%。②基于中性假设的空气动力学阻力估算方法在一定程度上高估了空气动力学阻力,导致PET存在低估现象(RMSE=25.82 W/m2),且误差偏离随着PET增大而愈加明显。③在当地条件下当量空气动力学阻力■与风速呈显著的指数关系(■,R2=0.50,P<0.05,N=394),基于该关系估算的PET相对于中性假设而言具有更高的精度(R2提高了3.26%,RMSE... 相似文献
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祁连山南麓河谷地形云生长的层结特征 总被引：1，自引：1，他引：0
2007-07～08在祁连山进行了地形云结构及形成机理的外场观测,利用获取的探空观测资料分析地形云生长的层结结构特征.结果表明:地形对层结特征的影响是非常明显的,风速在河谷内随高度的变化较小,在河谷上部接近山脉高度的区域存在一过渡层;夜间边界层风向以偏西北山风为主,白天低层以偏东谷风为主,高层以偏西气流为主,存在风向切变.温度层结各时次基本一致,夜间易形成逆温层.湿度层结受地形的影响最为明显,在山脉高度以下区域维持着逆湿状况,其形成与河谷内局地环流以及山脉对气流的阻滞作用有关.对试验期间各类天气形势下的层结特征分析结果表明:西南气流移动型中,双层不稳定的层结结构对地形云的生长极为有利;在阻塞型中,由于高原高值系统对西南气流的阻塞,使水汽不能够进入高原东北部.西北气流冷平流型和河套冷涡型下,由湿静力不稳定层结和冷平流引起的不稳定层结对地形云的发展较为有利.平直西风气流下,只在局地形成地形对流性降水. 相似文献
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利用巴丹吉林沙漠北缘拐子湖流沙下垫面2013年7、10月和2014年1、4月的湍流通量资料，计算并分析了研究区近地层湍流强度，同时针对风速分量、温度、水汽和CO2归一化标准差随稳定度的变化关系和总体输送系数等陆面过程特征进行分析。结果表明：（1）风速各分量的湍流强度均随风速的增加逐渐减小，风速处于2 m·s-1以下时湍流发展最为旺盛。湍流强度主要由水平方向风速分量决定，垂直方向风速的作用较小，且近中性和不稳定层结利于湍流的发展。与其他地区相比，平坦且没有建筑物的沙漠地区，机械湍流较弱，湍流强度相应较小。（2）风速各分量的归一化标准差与稳定度（z/L）均满足1/3次方函数规律，其中垂直方向风速分量的拟合曲线方程较好。（3）动量输送系数Cd具有明显的夏季高、冬季低的变化状态且各月的日变化形态均呈夜间低、日间高的循环形态。热量输送系数Ch的不同月份日变化间并没有明显的排列次序，且日出日落前后具有明显的波动。不稳定层结时，Cd和Ch均随风速的增加逐渐减小；稳定层结时，Cd和Ch均随着风速的增加逐渐上升。 相似文献
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戈壁风蚀面与植被覆盖面地表性质粗糙度长度的确定 总被引：9，自引：5，他引：4
以Monin-Obukhov相似性理论为基础, 利用量纲分析法分别推导出不同层结稳定度下确定戈壁风蚀面与植被覆盖面空气动力学参数的物理模型, 并利用该模型研究了粗糙度长度与粗糙元性质, 流经近地层流体特征以及大气层结稳定度之间的关系。得出以下结论: 戈壁风蚀面上空气动力学粗糙度长度与砾石粒径、高度、覆盖度、自由风速、摩擦速度以及大气层结稳定度有关; 植被覆盖面空气动力学粗糙度长度取决于植被类型、植被高度、覆盖度、零平面位移高度、自由风速、摩擦速度以及大气层结稳定度。 相似文献
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2010年4月24日民勤出现黑风天气,给当地经济和社会造成严重影响。利用民勤黑风发生前后2010年4月24日08时~25日08时的探空观测资料,对大气不稳定能量、热力参数“V—3θ”和动力参数“相对风暴水平螺旋度”进行了计算分析。结果表明：黑风发生时,民勤近地面存在正不稳定能量,促使黑风在近地面层爆发性发展,使沙尘粒子在正不稳定能量区聚积,形成黑风墙。民勤黑风爆发前和爆发时大气温湿结构呈现出上湿下干的分布特征,低层湿度较小不利于降水产生,为沙尘扬起提供了较好的垂直方向的环境场条件;黑风爆发前大气层结500 hPa以下风场的垂直分布形成顺时针滚流,为对流性不稳定层结,气层有利于黑风生成和发展;黑风过境后,风场的垂直分布顺时针滚流下降至700 hPa以下,说明大气层结的对流不稳定层结变薄、减弱,700～500 hPa存在逆时针滚流,抑制上升运动,预示黑风将减弱。黑风爆发期间在河西走廊中部存在一个相对风暴水平螺旋度负值中心,中心值达到-870 m2 /s2,远小于强沙尘暴发生的临界值-600 m2 /s2,沙尘暴的强度与相对风暴水平螺旋度负值中心存在很好的对应关系。当民勤测站的相对风暴水平螺旋度＜0,其上游存在≤-600 m2 /s2的最小中心时,民勤测站将出现强沙尘暴;当民勤测站的螺旋度＜0,其上游存在正值中心时,下游存在负值中心时,民勤测站的沙尘暴结束,能见度好转。 相似文献
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半干旱区沙尘天气近地层湍流通量及起沙研究 总被引：4，自引：3，他引：1
利用2005年春季朱日和气象站20 m气象塔的观测资料,结合同期的PM10质量浓度资料,分析了半干旱地区不同沙尘天气下近地层湍流通量的变化特征以及PM10质量浓度与起沙之间的关系。结果表明,动量通量在15:00左右达到极大值;感热通量在白天为正值,中午12:00左右达到峰值,而晚上变为负值,并在凌晨达到谷值;由于3月份下垫面湿度大,导致潜热通量经常全天为正值,并在16:00左右达到峰值;PM10质量浓度与摩擦速度的二次方呈正比,临界起沙风速和临界摩擦速度分别为7 m·s－1和0.7 m·s－1。 相似文献
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We investigated the effects of morphologic position and discharge on flow structure in a steep (0.10 m/m) mountain channel by collecting three-dimensional measurements of time-averaged and turbulent velocity components with a SonTek FlowTracker Handheld ADV (acoustic Doppler velocimeter) on a 30-m reach of a step-pool channel in the Colorado Rockies. Velocity profiles were measured at morphologic positions characteristic of steep channels (above steps, step lips, base of steps, pools, cascades, runs), and at five different discharges. A marked three-dimensionality of flow structure was documented in East St. Louis Creek. Velocities in the streamwise component were the largest contributors to overall velocity vector magnitudes; cross-stream and vertical components contributed averages of 20% and 15%, respectively, to overall vector magnitudes. Turbulence intensities were especially multi-dimensional, however, with large contributions to turbulent kinetic energy from the vertical component of velocity. Analysis of variance indicated that discharge and morphologic position significantly affected mean streamwise velocities, with substantially higher velocities upstream from steps than in pools. Discharge and morphology effects on cross-stream and vertical velocity components, however, were not significant. Discharge and morphologic position also significantly affected turbulence intensities for all flow components, with the greatest turbulence intensities occurring in pools and at high discharges. These results illustrate the strong discharge-dependence of hydraulics in step-pool channels, where relative submergence of bedforms changes rapidly with discharge, and the substantial spatial variation in hydraulics created by step-pool sequences. 相似文献
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Based on preliminary theoretical analysis and numerical experiment, it is found that land surface heterogeneity plays an important role in the models turbulent flux calculation. In nearly neutral atmosphere conditions, variation coefficient of sub-scale roughness length, cell-average roughness, and reference height are main factors affecting the calculation of grid turbulent fluxes. The first factor has a determinant role on calculation deviation. The relative error generated by roughness heterogeneity could be more than 40% in some cases in certain areas (e.g., in vegetation-climate transition belt). Selecting a specific reference height may improve the calculation of turbulent flux. In stable or unstable atmosphere conditions, with sensible heat flux as an example, analysis shows that the discrepancy is correlated to the sub-grid distributions of mean wind velocity, potential temperature gradient between land surface and reference levels, and atmosphere stability near surface layer caused by the heterogeneity of land surface roughness. The calculation of turbulent flux is the most sensitive to stability in the above three factors. The above analysis shows that it is necessary to make a further consideration for the calculation deviation of the turbulent fluxes brought from land surface heterogeneity in the present numerical models. 相似文献
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利用2007/2008年中国第24次南极考察队在南极中山站附近冰盖上观测试验获得的湍流脉动及相关资料,对原始资料通过坐标旋转订正后,应用涡动相关法计算分析了冰盖近地面层的湍流强度(I)、稳定度参数(z/L)、摩擦速度(u*)、拖曳系数(Cd)、地表粗糙度(z0)及动量通量(τ)和感热通量(H),并与空气动力学方法的计算结果进行对比。结果表明,Louis方案能够较好地模拟近地面层湍流通量;在平均状态下,全天雪面以感热形式从大气获得净的能量;近中性层结下地表粗糙度z0为4.54×10-4m,拖曳系数Cd=1.7×10-3,在非中性条件下,稳定度越小Cd越大,反之,则稳定度越大Cd越小。 相似文献
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塔克拉玛干沙漠塔中地区春夏季风蚀起沙研究 总被引：6，自引：5，他引：1
利用塔克拉玛干沙漠腹地塔中地区的观测资料,对塔中地区春夏季地表土壤风蚀起沙的临界摩擦速度及其变化特征和起沙风速进行了分析研究,并计算了2008年4月19日和7月19日两次沙尘暴天气过程沙漠地表的风蚀起沙量。结果表明:塔中地区春夏季地表起沙的临界摩擦速度为0.26 m·s-1;2 m高度的临界起沙风速约为4.1 m·s-1;两次沙尘暴过程的顺风向沙粒通量和垂直尘粒通量的平均值分别为17.44×10-4 kg·m-1·s-1 、13.8×10-8 kg·m-2·s-1、164.69×10-4 kg·m-1·s-1和799.77×10-8 kg·m-2·s-1;沙尘通量的变化与风速及摩擦速度的变化具有一致性。 相似文献
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Sonic anemometers in aeolian sediment transport research 总被引：3，自引：0，他引：3
Fast-response wind and turbulence instruments, including sonic anemometers, are used more and more in aeolian sediment transport research. These instruments give information on mean wind, but also on fluctuations and turbulent statistics, such as the uw covariance, which is a direct measure of Reynolds' stress (RS) and friction velocity. This paper discusses the interpretation of sonic anemometer data, the transformations needed to get proper results and turbulence spectra, and how they are influenced by instrument size, sampling frequency, and measurement height.Turbulence spectra characterize how much the different frequencies in the turbulent signals contribute to the variance of wind speed, or to the covariance of horizontal and vertical wind speed. They are important in determining the measurement strategy when working with fast-response instruments, such as sonic anemometers, and are useful for interpreting the measurement results. Choices on the type of sonic anemometer, observation height, sampling period, sampling frequency, and filtering can be made on the basis of expected high and low-frequency losses in turbulent signals, which are affected by those variables, as well as wind speed and atmospheric stability.Friction velocity and RS, important variables in aeolian sediment transport research, are very sensitive to tilt or slope errors. During a field experiment, the slope sensitivity of the RS was established as 9% per degree of slope, which is 1.5 times the value reported in literature on the basis of theoretical considerations. An important reason for the difference probably is the large influence of streamline curvature on turbulence statistics and thereby on the slope sensitivity of the RS. An error of 9% per degree of slope in the RS will translate into an error of approximately 4% per degree of slope in the calculated friction velocity.Space–time correlation of the horizontal wind speed is much larger than that of the vertical wind speed and the instantaneous RS. This largely explains why, in previous studies, a poor correlation was found between instantaneous RS measured at 3 m height and saltation flux near the surface, whereas the correlation between wind speed at some height and saltation flux was much better. Therefore, the poor correlation between RS away from the surface and saltation flux does not contradict that saltation flux is caused by RS. 相似文献
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Velocity profile of a sand cloud blowing over a gravel surface 总被引：2，自引：0，他引：2
Particle dynamic analyzer (PDA) measurement technology was used to study the turbulent characteristics and the variation with height of the mean horizontal (in the downwind direction) and vertical (in the upward direction) particle velocity of a sand cloud blowing over a gravel surface. The results show that the mean horizontal particle velocity of the cloud increases with height, while the mean vertical velocity decreases with height. The variation of the mean horizontal velocity with height is, to some extent, similar to the wind profile that increases logarithmically with height in the turbulent boundary layer. The variation of the mean vertical velocity with height is much more complex than that of the mean horizontal velocity. The increase of the resultant mean velocity with height can be expressed by a modified power function. Particle turbulence in the downwind direction decreases with height, while that in the vertical direction is complex. For fine sands (0.2–0.3 mm and 0.3–0.4 mm), there is a tendency for the particle turbulence to increase with height. In the very near-surface layer (<4 mm), the movement of blown sand particles is very complex due to the rebound of particles on the bed and the interparticle collisions in the air. Wind starts to accelerate particle movement about 4 mm from the surface. The initial rebound on the bed and the interparticle collisions in the air have a profound effect on particle movement below that height, where particle concentration is very high and wind velocity is very low. 相似文献
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不同绿洲分布对局地气候影响的数值模拟 总被引：34，自引：13，他引：21
使用非静力平衡中尺度模式MMSV3,通过数值模拟,研究了不同绿洲分布对局地气候的影响,分析了不同绿洲、林带分布状况下的地表能量平衡,以及对边界层特征的影响,为荒漠化治理提供一定的理论依据。研究结果表明:沙漠化后感热增大,潜热减小,地表温度升高,5d内可升高0.7℃,土壤温度也有类似的变化,只是变化幅度小,并存在滞后效应,摩擦速度减小,5d内可减小5cm·s-1,长期下去,将形成风沙肆虐,沙尘暴频繁的气候,为人类敲响了警钟;而绿化可使潜热增大,对城市影响更为明显,潜热将增大两倍,地表温度降低,湿度增大,摩擦速度明显增大,可以有效地阻止沙尘暴的发生,对半干旱地区环境治理大有好处。 相似文献
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Height profile of the mean velocity of an aeolian saltating cloud: Wind tunnel measurements by Particle Image Velocimetry 总被引：3，自引：0，他引：3
The velocity of saltating particles is an important parameter in studying the aeolian sand movement. We used Particle Image Velocimetry to measure the variation with height of the mean particle velocity of a saltating cloud over a loose sand surface in a wind tunnel. The results suggest that both the horizontal and vertical particle velocities fit the Gaussian distribution well, and that the mean particle velocity of a saltating cloud varies with wind velocity, particle size and the height above bed. The mean horizontal velocity is mainly the result of acceleration by the wind and increases with an increase in friction wind velocity but decreases with an increase in grain size because greater wind velocity causes more acceleration and finer particles are more easily accelerated at a given wind velocity. It also increases with an increase in height by a power function, in agreement with previous results obtained by other methods such as the high-speed multi-flash photographic method and Particle Dynamics Analyzer (PDA), reflecting, first, the increase in wind velocity with height through the boundary layer, and second, the longer trajectory-particle path length increases with height and affords a longer time for acceleration by the wind. An empirical model relating the mean horizontal particle velocity and height, friction wind velocity as well as particle size is developed. The ratio of the mean horizontal particle velocity to the clean wind velocity at the same height increases with height but decreases with grain size. The magnitude of mean vertical velocity is much less (one or two orders less) compared with the mean horizontal velocity. The average movement in the vertical direction of a saltating cloud is upward (the mean vertical velocity is positive). Although the upward velocity of a saltating particle should decrease with height due to gravity the mean vertical (upward) velocity (the average of both ascending and descending particles) generally shows a tendency to increase with height. It seems that at higher elevations the data are more and more dominated by the ‘high-flyers’. The underlying mechanism for the mean vertical velocity distribution patterns needs to be clarified by further study. 相似文献