TIPEX高原东南部近地层湍流参数的分析

The characteristics of the turbulence spectrum, turbulence variance, and turbulence flux at Qamdo overthe Southeastern Tibetan Plateau measured during the TIPEX experiment from 18 May to 30 June 1998are analyzed by the eddy correlation method. During periods of intense convection, most of the spectraof the 3D winds, temperature, and humidity follow a power law with a slope of -2/3. The normalizedvariances of the 3D winds in relation to z/L satisfy the similarity law but the normalized variances oftemperature and humidity are related to z/L by a -1/3 power law only in unstable conditions. In near-neutral stratification, σu/u* and σy/u* at Qamdo and Gerze are nearly constant in rugged terrain andσw/u* at Qamdo and Gerze is similar to the value found in plains, which indicates that the, effects oflandform on vertical turbulence is not significant over the southeast and western Tibetan Plateau. Duringthe dry period, the sensible heat dominates, comprising 81% of the heat intensity, with the other 19%being latent heat; during the wet period on the other hand, the latent heat accounts for about 64% ofthe available energy and the sensible heat only around 36%. The maximum intensity of the heating of airoccurs in the middle of the Plateau during the summertime.     

黑河下游绿洲近地层湍流输送特征研究

分析2003年9月5-27日在黑河下游额济纳绿洲取得的近地面层湍流观测资料,讨论无量纲湍流方差与稳定度参数Z/L的关系.无量纲风速分量σu/u*、σv/u*和σw/u*在不稳定层结与稳定度Z/L满足1/3次方时,符合Monin-Obkuhov相似理论.在近中性时,σu/u*、σw/u*值比平坦下垫面的略小些,σv/u*值比平坦下垫面的略大.无量纲温度脉动方差和湿度脉动方差在对流状态下与Z/L满足-1/3次方,在稳定和不稳定层结下,随|Z/L|减小而增大.地面热量以感热输送为主,感热通量峰值约为250 W/m2,潜热通量的峰值为170 W/m2;夜间潜热通量较小,感热通量则出现负值.动量通量日间平均在0.2-0.3 N/m2,峰值为0.31 N/m2.黑河下游绿洲柽柳林动力学粗糙度比HEIFE戈壁及其他绿洲下垫面的大,中性时z0m=0.47551 m.中性状态下动量整体输送系数CD=22.2×10-3,不稳定层结时平均值CD=10.3×10-3,稳定层结时平均值CD=7.2 × 10-3.热量整体输送系数CH,中性状态下CH=3.2 × 10-3,不稳定层结时平均值为CH=3.3×10-3,稳定层结时平均值为CH=2.7×10-3.     

青藏高原不同地区湍流输送特征及其与气象因子的关系

利用第三次青藏高原大气科学观测试验数据,对高原不同地区感热、潜热交换等湍流输送特征进行了分析,并进一步对比研究了其与气象环境因子的相关关系。结果表明:（1）高原各站之间感热和潜热的差异性较大,但大多在雨季潜热会大于感热。干燥的狮泉河站属于高寒荒漠地区,降水极少,全年感热都远大于潜热,波文比年平均值可达到20.0;湿润的比如站和嘉黎站潜热在4～10月均显著大于感热,波文比在4～10月的数值范围在0.27～0.88。（2）高原感热和潜热通量的季节变化与高原季风所处的地理位置有密切关系,高原中部的感热通量在3～5月达到最大值,而高原西部则在4～6月最大,可能与高原季风的活动有关。（3）通过与气象要素的相关分析表明,高原西部狮泉河站感热与地气温差的正相关关系最为显著,全年的相关系数可以达到0.905,在4个季节相关系数也均大于0.79,这可能与下垫面是裸地有关;高原中部安多站和那曲站感热与风速的正相关在夏季最为显著,比如站感热与风速的正相关在冬季最为明显,而狮泉河站感热与风速在春、夏季均有着十分显著的正相关。     

HEIFE戈壁地区近地层大气的湍流结构和输送特征

根据黑河地区地气相互作用实验研究(HEIFE)1988年POP和1990年PIOP实验的观测资料,分析了戈壁地区近地层大气的湍流结构,主要是风速分量和温度方差的相似关系,以及各有关量的功率谱和湍流通量的协谱。1988年POP期间发现的戈壁近地层大气中白天经常出现的水汽由上而下输送等特殊现象,在1990年PIOP中得到进一步的验证。文中分析了有关物理机制,认为这一现象和众所周知的“绿洲效应”是戈壁-绿洲这一地区性中尺度环流影响的两个侧面。     

应用涡旋相关方法对戈壁地区湍流输送特征的初步研究

利用微机技术建立了一个较为廉价的近地层大气湍流数据实时采集处理系统,在1988年黑河预实验中工作良好,取得了一套较为完整的数据。对戈壁沙滩点的风、温、湿湍流脉动数据进行统计分析和涡旋相关方法处理,结果表明近地层大气的湍强特征符合一般规律。通量分析指出,戈壁地区的水汽通量在白天的绝大多数小时都呈负值(向下),而夜间为正。文中对湍流谱的特征也进行了初步分析。     

青藏高原东部草甸下垫面涡旋相关观测数据的质量控制及评价研究

目前利用涡旋相关仪观测地表通量的方法已被广泛采用, 但由于涡旋相关法是建立在方程假设简化的基础上, 这对观测数据的质量提出了一定的要求, 所以对观测数据的处理及通量结果的质量状况分析就显得尤为重要。本文以理塘站2006年7月中到8月中的数据为例, 对其进行质量控制, 并将质量控制后的通量计算结果与原始值进行比较。质量控制后感热通量和潜热通量总和有所增长, 动量通量值则受质量控制影响较大。质量评价的结果为:动量通量、感热通量、潜热通量中高质量数据所占比例为68.2%、60.6%、63.3%。     

青藏高原东南部墨脱地区弱降水微物理特征的Ka波段云雷达观测研究

藏东南地区的墨脱县位于雅鲁藏布江下游的河谷区域,是印度洋水汽进入高原的最主要水汽通道。墨脱作为西藏年平均降水量最多的地区,是青藏高原云降水系统的重要组成部分。本文以2020年墨脱地区的Ka波段云雷达观测数据为基础,首先对云雷达功率谱数据进行预处理,并采用降水现象仪对云雷达观测进行验证。在此基础上,选取了2020年3月6日和8月24日具有层状云降水特性的两次弱降水过程,利用云雷达功率谱数据反演了雨滴谱,探究墨脱地区旱季和雨季弱降水的微物理特征。结果表明:云雷达观测与降水现象仪雨滴谱数据计算的Ka波段云雷达回波强度理论值存在大约12 dB的系统误差,订正之后二者随时间变化一致性较好,云雷达反演的近地面雨滴谱特征与降水现象仪观测接近。墨脱地区零度层高度随季节变化明显,旱季零度层高度较低（例如地面上1.5 km左右）,而雨季零度层高度较高（例如地面上4 km左右）。墨脱层状云雨滴谱的宽度较窄,降水粒子直径不超过3 mm。在零度层以上,根据谱偏度和峰度的垂直变化可以推测冰晶粒子直径随高度下降缓慢增长, 但旱季冰晶粒子增长比雨季更为明显。经过零度层后,冰晶粒子转化为雨滴,雨滴在下落过程中由于碰并及蒸发作用造成浓度减小,直径越小的粒子浓度减小越快。在近地面,由于蒸发作用的加强导致随高度降低雨滴浓度明显减小。     

简单生物圈模式 (SiB2) 中湍流能量通量对近地层两类阻抗系数的敏感性研究

陆—气之间的能量交换是通过近地层湍流热量和水汽通量来实现的.以往的研究表明近地层阻抗对湍流能量通量有着不同程度的影响,但是关于陆面模式中阻抗系数的取值范围却始终没有统一的标准.为了深入了解简单生物圈模式 (SiB₂) 中近地层阻抗系数取值变化对湍流能量通量的影响,我们以那曲站为例,分别采用传统的逐个因子分析法和考虑参数间相互作用的部分因子分析法定量地研究了夏季该观测站近地层湍流能量通量分别对冠层阻抗系数C₁和地表阻抗系数C₂的敏感性响应.结果表明,感热通量对地表阻抗系数C₂更为敏感,而潜热通量则对冠层阻抗系数C₁较为敏感;感热通量随C₁增加而增大,随C₂增加而减小,而潜热通量则随C₁或C₂的增加而减小;不管是感热通量还是潜热通量,它们对阻抗系数的敏感度随阻抗系数的增大而减小,而对阻抗系数的相对敏感度则随阻抗系数的增大而增大.最后,结合那曲站夏季下垫面稀疏短草的分布特点分析了造成感热通量和潜热通量敏感变化各异的原因.     

Measurements Of Turbulence Transfer In The Near-Surface Layer Over The Southeastern Tibetan Plateau

Turbulent flux measurements at Qamdo site over the Tibetan Plateau during TIPEX from May 18 to June 30, 1998 are presented. Sensible heat dominated,accounting for about 66% of the available energy (the sum of net radiation and soil heat flux) prior to the monsoon(dry period), reducing to about 31%, with latent heat increased to about 56% of available energy,in the monsoon season (wet period). Surface energy budget closure on average was about 0.80 (0.85)prior to the monsoon and 0.89 (0.76) during the monsoon using eddy correlation (profile) methods. The sum of latent and sensible heat fluxes calculated from the flux-profilemethod was smaller by about 15% than that from eddy correlation. Martano's method is used toestimate the surface aerodynamic roughness length z₀ and zero plane displacement d from singlelevel sonic anemometer data, giving d = 0.12 m and z₀ = 0.08 m. The overall neutral dragcoefficient (C_DN) and scalar coefficient (C_HN) were found to be C_DN = 0.0055and C_HN = 0.0059 in the southeastern area of Tibet. Their variations with the mean wind speed at 10 m are discussed.     

Determination of the Drag Coefficient over the Tibetan Plateau

In this paper,a preliminary study is given on the drag (i.e.bulk transfer for momentum) coefficient,on the basis of data from four sets of AWS in Tibet during the first observational year from July 1993 to July 1994 according to China Japan Asian Monsoon Cooperative Research Program.The results show that the drag coefficient over the Tibetan Plateau is 3.3 to 4.4×103.In addition,monthly and diurnal variations of drag coefficient and the relationship among the drag coefficients and the bulk Richardson number,surface roughness length and wind speed at 10 m height are discussed in detail.     

青藏高原六套陆面蒸散发产品的评估

Uncertainties in the evapotranspiration (ET) products used in the Tibetan Plateau (TP) region were determined based on the data from satellite remote sensing and observations having different spatial and temporal resolutions, limiting their utility for hydrometeorological and climate assessment. Six ET (PML, EB-ET_V2, GLEAM, GLDAS, ERA5_Land, and MOD16) products were evaluated based on eddy observations, and the differences between the products were compared. Moreover, the uncertainties in ET products in the TP region were analyzed. The results of the analysis are as follows: (1) A good correlation and consistency exist in the mean state and seasonal cycle between the observed and ET values of the corresponding pixel. Moreover, GLEAM product exhibits a high degree of agreement with the observed values and has applicability, and MOD16 product exhibits poor performance at most sites. (2) In terms of seasonal changes, ERA5_Land product values are highly consistent with the observed changes during spring, GLEAM product values are nearly consistent with the observed changes during summer and winter, and EB-ET_V2 product values are highly consistent with observed values during autumn. (3) Spatially, GLEAM product has higher correlation (the correlation coefficient R＞ 0.88) and consistency (index of agreement IOA＞ 0.89) compared to those of EB-ET_V2 product and GLDAS product. Substantial differences exist in the temporal and spatial distribution of various products during different seasons, especially during spring. Compared with other products, MOD16 product is underestimated in summer and overestimated in winter in most regions. (4) The annual average ET for each product except for MOD16 product is considerably different. The annual average ET values of the remaining five products over multiple years arranged in descending order are as follows: ERA5_Land product (401.46 mm a−1)＞ PML product (334.37 mm a−1)＞GLEAM product (298.46 mm a−1)＞EB-ET_V2 product (271.39 mm a−1)＞GLDAS product (249.67 mm a−1). The total annual evaporation in the TP region is 330.59 mm a−1. The assessment results provide a detailed understanding of the quality and dynamics of ET products in the TP region, which can serve as reference data for regional water management and water resource assessment in the TP region. © 2023 Science Press. All rights reserved.     

高原东南缘大气近地层湍能特征与边界层动力、热力结构相关特征

基于云南省大理2008年3、5、7月GPS加密探空试验时段(14和02时)资料,结合边界层铁塔综合观测资料,采用温度梯度法、逆温强度法和涡动相关法分别计算高原东南缘对流边界层(convective boundary layer,CBL)及稳定边界层(stable boundary layer,SBL)顶高度,通过计算获取感热通量、潜热通量、湍流动能、切变项以及浮力项与大气动力、热力过程垂直相关特征综合分析,可发现湍能方程中浮力项、感热、潜热通量与NCEP再分析资料计算获取的大气视热源相关特征显著,这某种程度反映了高原东南缘近地层大气湍流动量、热量输送对低层大气视热源Q_1的重要贡献。低层视热源Q_1亦表现出与湍能方程分量类似的日变化周期,此特征反映了高原东南缘大气热源变化与下垫面水热过程及其湍流输送日变化密切相关;浮力项与湍能等项对大气低层热源与涡动特征、热力混合结构的形成有重要作用;低层大气视热源、水汽汇均与边界层高度有显著相关,综合分析结果某种程度描述了青藏高原东南缘近地层湍流动量、热量输送状况与低层大气热源,热力混合边界层结构的综合相关物理图像,初步探索了高原东南缘对流活跃区大气湍流运动与大气动力、热力过程相互作用特征。研究表明近地层湍流通量变化某种程度可反映未来局地大气视热源垂直结构变化的"强信号"特征。本文上述研究结论也可启发我们进一步关注近地层湍流通量异常变化特征及其对局地降水过程大气热源结构演变的影响问题。     

由声雷达回波反演湍流场结构系数

定量测量声雷达回波强度可以导出大气温度结构系数（Ct 2）和速度结构系数（Cv2）。文章简要回顾和评述了过去的工作,并讨论了逾量衰减、风和湍流等因素对该测量的影响。研究表明：逾量衰减主要是由速度场的不均匀性所造成。其次,风场也有不可忽视的衰减作用,在风速达10 m/s时,引起的衰减达50%以上。最后给出了改进后的声雷达方程和反演Ct2和Cv2的方法。初步的试验结果对理论的应用是支持的。     

青藏高原改则地区近地层湍流特征

分析了第二次青藏高原气象科学试验（TIPEX）1998年6～7月加强期在改则取得的湍流资料,讨论了近地层湍流宏观统计量、温度、湿度结构参数以及通量整体输送系数等变化规律,结果表明在不稳定层结下,湍流宏观统计量等随稳定度的变化满足过去在平原地区得到的相似关系。     

Analysis of Turbulence Characteristics over the Northern Tibetan Plateau Area

Based on CAMP/Tibet [Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau] turbulent data collected at the Bujiao (BJ) site of the Nagqu area, the turbulent structure and transportation characteristics in the near surface layer during summer are analyzed. The main results show that the relationship between the normalized standard deviation of 3D wind speed and stability satisfies the similarity law under both unstable and stable stratifications. The relations of normalized standard deviation of temperature and specific humidity to stability only obey the “?1/3 power law” under unstable conditions. In the case of stable stratifications, their relations to stability are dispersing. The sensible heat dominates in the dry period, while in the wet period, the latent heat is larger than the sensible heat.     

青藏高原东坡理塘地区近地层湍流特征研究

利用中国气象局成都高原气象研究所在青藏高原东坡理塘地区建立的大气综合观测站观测资料, 以2006年1月和7月涡旋相关资料分别代表冬季和夏季, 分析和比较了该地区近地层包括风速、 风向、 大气稳定度在内的平均场特征, 以及湍流强度、 无量纲化风脉动方差相似性和地表通量变化特征,结果表明, 1月和7月稳定度基本集中在±0.5和±0.25之间; 湍流在<2 m·s-1的风速环境中发展最为旺盛, 随着风速的增大湍流强度减小迅速; 无量纲化三维风脉动方差符合Monin-Obukhov相似理论的“1/3”定律, 其最佳通用相似函数在稳定和不稳定条件下都可以拟合得到; 地表通量均表现出明显的日变化特征, 1月以感热为主, 潜热很小; 7月以潜热为主, 感热较小。     

Turbulent Flux Measurements Above and Below the Overstory of a Boreal Aspen Forest

Turbulent flux measurements both above and beneath the canopy of a boreal aspen forest are described. Velocity skewness showed that, beneath the aspen canopy, turbulence was dominated by intermittent, downward penetrating gusts. Eulerian horizontal length scales calculated from integration of the autocorrelation function or spectral peaks were 9.0 and 1.4 times the mean aspen height of 21.5 m respectively. Above-canopy power spectral slopes for all velocity components followed the -2/3 power law, whereas beneath-canopy slopes were closer to -1 and showed a spectral short cut in the horizontal and vertical components. Cospectral patterns were similar both above and beneath the canopy. The Monin–Obukhov similarity function for the vertical wind velocity variance was a well-defined function of atmospheric stability, both above and beneath the canopy. Nocturnal flux underestimation and departures of this similarity function from that expected from Monin–Obukhov theory were a function of friction velocity. Energy balance closure greater than 80% was achieved at friction velocities greater than 0.30 and 0.10 m s-1, above and below the aspen canopy, respectively. Recalculating the latent heat flux using various averaging periods revealed a minimum of 15 min were required to capture 90% of the 30-min flux. Linear detrending reduced the flux at shorter averaging periods compared to block averaging. Lack of energy balance closure and erratic flux behaviour led to the recalculation of the latent and sensible heat fluxes using the ratio of net radiation to the sum of the energy balance terms.