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.     

藏北高原草甸下垫面近地层能量输送及微气象特征

利用GAME/Tibet 1998年IOP观测资料,分析研究藏北高原草甸下垫面近地层的地面加热场、地表能量平衡、地面阻曳系数CD及感热通量整体输送系数CH等特征,得到了一些有关藏北高原草甸下垫面近地层能量输送及微气象特征结构的新认识.     

长江三角洲常熟地区近地层湍流特征的研究

利用1999年5～9月长江三角洲常熟地区的湍流脉动观测资料,分析了该地区感热、潜热和动量通量的日变化以及湍流强度和湍流谱特征,结果表明该地区各能量的日变化与常见情况相同,白天潜热通量的输送占主导地位,感热通量比潜热小得多,且湍流的日变化与天气的关系非常密切,晴天比阴天要大得多.湍流强度和湍流谱的分析结果表明,在近中性条件下,常熟地区各方向湍流强度接近典型平坦下垫面的值.非中性条件下,垂直方向规一化标准差与稳定度的关系都较好地满足1/3次幂定律,水平方向没有垂直方向上的规律好,特别是稳定条件下,数据点分散性大;各风速分量谱在高频段满足理论上的-2/3次幂定律,纵向和垂直方向速度谱的峰值频率与典型平坦下垫面上的结果一致.总体输送系数CD、CH与稳定度的关系密切,随稳定度增加有减小的趋势.     

长江三角洲常熟地区近地层湍流特征的研究

利用1999年5－9月长江三角洲常熟地区的湍流脉动观测资料，分析了该地区感热，潜热和动量通量的日变化以及湍流强度和湍流谱特征，结果表明：该地区各能量的日变化与常见情况相同，白天潜热通量的输送占主导地位，感热通量比潜热小得多，且湍流的日变化与天气的关系非常密切，晴天比阴天要大得多。湍流强度和湍流谱的分析结果表明，在近中性条件下，常熟地区各方向湍流强度接近典型平坦下垫面的值。非中性条件下，垂直方向规一化标准差与稳定度的关系都较好地满足1／3次幂定律，水平方向没有垂直方向上的规律好，特别是稳定条件下，数据点分散性大；各风速分量变在高频段满足理论上的－2／3次幂定律，纵向和垂直方向速度谱的峰值频率与典型平坦下垫面上的结果一致，总体输送系数CD，CH与稳定度的关系密切，随稳定度增加有减小的趋势。     

黄土高原半干旱草地近地层湍流温湿特征及总体输送系数

利用兰州大学半干旱气候与环境观测站(简称SACOL站)2008年夏季晴天近地层湍流观测资料,分析了SACOL站近地层湍流温、湿统计特征,确定了大气动力学和热力学粗糙度长度,讨论了总体输送系数随大气稳定度的变化规律。结果表明,大气层结不稳定条件下,无量纲温度和比湿脉动方差与稳定度Z/L之间均满足-1/3次规律;大气层结稳定条件下,温湿脉动方差总体趋势是随大气稳定度增加而减小。水汽通量全天大于零,最大值为0.063 g·m-2·s-1,地表日平均蒸发量为1.9 mm。中性条件下,黄土高原半干旱草地动力学粗糙度长度为6.6×10-3m,热力学粗糙度为1.85×10-5m。大气层结不稳定条件下,CD平均值为4.4×10-3,CH平均值为3.9×10-3;中性条件下,CD和CH平均值分别为4.2×10-3和2.8×10-3;层结稳定条件下,CD平均值为3.1×10-3,CH平均值为2.1×10-3,表明总体输送系数随稳定度的增大而减小。     

青藏高原中部聂荣半干旱草地夏季近地层能量平衡与输送分析

利用青藏高原中部聂荣地区草地下垫面2014年7~8月近地层气象要素梯度观测及湍流观测数据,分析讨论了该地区观测期间的基本气象要素特征、能量平衡特征以及能量输送特征,主要结论如下:(1)向下、向上短波辐射和净辐射日变化规律一致,向下、向上长波辐射日变化平缓。反照率呈"U"型分布,早晚大,中午小,聂荣夏季地表平均反照率为0.20。(2)在夏季白天,聂荣地区净辐射大部分以潜热的形式加热大气。考虑了土壤浅层热储存和垂直运动引起的平流输送后,能量闭合率由0.65提高到0.80,闭合率有显著的提高。(3)在不稳定层结下,动量总体输送系数CD平均值为4.7×10~(-3)和热量总体输送系数CH平均值为3.5×10~(-3);在稳定层结下,CD平均值为3.4×10~(-3),CH平均值为1.8×10~(-3);C_D和C_H在近中性层结下的平均值分别为4.30×10~(-3)和2.39 10~(-3)。     

卫星遥感结合地面观测资料对中国西北干旱区地表热力输送系数的估算

本文利用黑河野外试验 (HEIFE) 地面观测资料, 采用空气动力学方法计算了干旱区内不同下垫面的地表热力输送系数CH, 结合由美国国家海洋和大气局 (NOAA) 系列卫星遥感观测的反映地表植被特征的归一化差值植被指数 (NDVI) 资料, 经拟合得到了针对我国西北干旱区不同下垫面的CH-NDVI参数化关系式, 并对此关系式进行了合理性检验。结果表明: 对于区域尺度而言, 在缺乏用其他方法获得较准确的区域CH值的情况下, 利用卫星遥感结合地面观测资料对其估算是较为可靠的方法。     

南海西南季风爆发前后海-气通量交换系 数研究

动量交换系数(CD)、感热交换系数(CH)和潜热(或水汽)交换系数(CE)是气候模式中参数化海-气通量必需的参数,不同地区、天气、海况的试验中计算结果各异。文章利用2002年4月24日至6月20日在西沙海区进行的第3次南海海-气通量观测试验资料,使用涡旋相关法和TOGA COARE2.5b版本通量计算方案,计算了西南季风爆发前后海-气界面动量、感热通量、潜热通量等的湍流交换系数,讨论了各通量交换系数的变化特征及其与气象要素变化的关系。结果表明:西南季风爆发前后,随着风向、风速、云量、降水、湿度及海面状态等变化,通量交换系数也发生变化:中性条件动量交换系数(CDn)在季风爆发前数值略小,季风爆发后数值增大;中性条件感热交换系数和潜热交换系数(CHn,CEn)对天气变化的反应不够敏感。动量交换系数主要受风速影响,但在不同风速区间相关关系有异。(CH)与海-气温差呈现正相关关系,和气温有明显的负相关关系。CE与风速的关系密切,但当风速>12 m/s,CE随风速的变化趋向一个稳定值。另外当海-气温差大约<2℃时,CE随着海-气温差增大相应增大,反映了通量交换系数不仅与风影响下的下垫面特性有关,而且还与稳定度参数有关。各通量交换系数与气象要素变化的关系可以拟合为多项式或者简单的线性关系式。     

基于淮河流域农田生态系统观测资料的通量研究

运用寿县国家气候观象台(代表淮河流域农田生态系统)2007年7月至2008年6月通量观测系统的观测资料,分析研究淮河流域农田生态系统的陆气相互作用,统计梯度和涡度数据缺测率,采用空气动力学(梯度)法和涡度相关法,验证通量观测系统观测数据的可靠性,分析CO2通量、潜热通量、感热通量的季节变化与日变化特征及其与下垫面的关系,计算出地表平均反照率、能量闭合率、动量输送系数等。结果表明:通量观测仪器测得的数据可靠,原始资料具有客观性、可用性;CO2等通量存在明显的季节变化,与下垫面状况有密切的关系,日变化均为单峰型分布,由通量观测系统的观测资料计算得到地表平均反照率为0.18,平均能量闭合率为0.92,平均动量输送系数为0.0092。     

黑河中上游不同下垫面动量总体输送系数和地表粗糙度对比分析

利用廓线法计算了黑河中上游地区盈科农田站、冰沟稀疏草地站、阿柔牧场站和大冬树山垭口积雪观测站的总体输送系数和地表粗糙度。结果表明,地表粗糙度与植被覆盖度和高度以及下垫面的性质有关,夏季地表粗糙度大小是农田站最大,其次是牧场站和稀疏草地站,高寒草甸站最小。下垫面状况还影响动量总体输送系数对稳定度的依赖程度,地表粗糙度大的地区强于地表粗糙度小的地区。     

荒漠戈壁大气总体曳力系数和输送系数观测研究

利用“我国西北干旱区陆一气相互作用观测试验”在甘肃敦煌进行的陆面过程野外试验的观测资料,依据三种不同方法确定了干旱戈壁区动量输送的曳力系数Cd、感热和潜热交换的总体输送系数Ch和Cq。结果表明：尽管这三种方法计算的曳力系数和总体输送系数有一定的差别,但在量级上相当,尤其是Cd和Ch的平均值比较接近。本文还通过对风向的分析,剔除了附近建筑物干扰和来自绿洲湿平流的影响,得到了荒漠戈壁总体输送系数的特征及其与理查孙数的关系。     

高原降雨天气过程中总体输送系数的变化特征

以中日亚洲季风机制合作研究计划设在西藏的4个自动气象站（AWS）获得的近6年（1995年7月-1999年6月）观测连续、时次密集的近地层大气梯度观测资料为基础,选取了高原中、东部夏季雨季的一些典型降雨过程,应用廓线-通量法计算了这些站降雨过程中每隔20min一次的总体输送系数,分析了其随层结稳定度、地表粗糙度以及在降雨天气过程中的变化特征。结果表明：总体输送系数的变化与近地层大气层结稳定度、地表粗糙度具有确定的、密切的关系;总体输送系数对降雨天气过程有明显的响应,但在与降雨过程的雨量峰值、降雨时段的对应上,各站的规律性略有不同。     

Inequality of eddy transfer coefficients for vertical transport of sensible and latent heats during advective inversions

Similarity of transport of water vapour and sensible heat was investigated within an advective inversion layer by measuring eddy fluxes together with gradients of temperature and humidity. The experimental site was a field of rice, grown under flood irrigation, which was situated in a semi-arid region. The fetch was about 300 m and local stabilities (z/L) over the rice ranged from 0 to 0.1. Results were expressed as the ratio of eddy transfer coefficients for sensible heat (K _H) and water vapour (K _w). Near neutral stability, K _H/K_W approached 1, but the ratio decreased to about 0.65 with increasing stability. Existing theory predicts the result qualitatively but accounts for only about one fifth of the decrease in K _H/K_W with stability.     

青藏高原总体输送系数的特征

利用中日亚洲季风机制合作研究计划设在西藏的 4个自动气象站（AWS）获得的5a多（199年7月～1998年12月）时次密集、观测连续的近地层梯度资料,以最小二乘法确定出相应站点各季节的地表粗糙度,并应用廓线-通量法计算了4站逐日的总体输送系数,分析了其随时间的变化特征。结果表明:青藏高原动量输送系数的多年平均值为3.53×10-3～4.99×10-3,热量输送系数为4.67×10-3～6.73×10-3,并且两种输送系数都存在明显的日变化和季节变化,部分站点还存在较明显的年际变化。另外,还讨论了总体输送系数与近地层大气层结稳定度、地表粗糙度以及地面风速等因子的关系,初步建立了可用常规气象站地面观测资料计算青藏高原总体输送系数的拟合公式。     

南海夏季风期间海-气通量整体输送系数分析

利用 2 0 0 0年南海海 气通量观测资料 ,建立了南海季风期间海 气通量整体输送系数的计算公式 ;同时 ,利用2 0 0 0和 2 0 0 2年观测资料与邻近海区同类公式进行了对比试验研究。结果表明 ,使用邻近海区的同类公式计算的海 气通量的误差高于新建立公式所得结果。因此 ,开展南海海 气通量观测试验对建立适合于南海的整体输送系数的计算公式是必要的     

Characteristics of Momentum and Heat Transfer over Semiarid Grasslands with Different Grazing Intensities in Inner Mongolia, China

The drag coefficient (C d) and heat transfer coefficient (C h) with the bulk transfer scheme are usually used to calculate the momentum and heat fluxes in meteorological models.The aerodynamic roughness length (z 0m) and thermal roughness length (z 0h) are two crucial parameters for bulk transfer equations.To improve the meteorological models,the seasonal and interannual variations of z 0m,z 0h,coefficient kB 1,C d,and C h were investigated based on eddy covariance data over different grazed semiarid grasslands of Inner Mongolia during the growing seasons (May to September) from 2005 to 2008.For an ungrazed Leymus chinensis grassland (ungrazed since 1979),z 0m and z 0h had significant seasonal and interannual variations.z 0m was affected by the amount and distribution of rainfall.kB 1 exhibited a relatively negative variation compared with z 0h,which indicates that the seasonal variation of z 0h cannot be described by kB 1.To parameterize z 0m and z 0h,the linear regressions between ln(z 0m),ln(z 0h),and the leaf area index (LAI) were performed with R 2 =0.71 and 0.83.The monthly average kB 1 was found to decrease linearly with LAI.The four-year averaged values of C d and C h were 4.5×10 3 and 3.9×10 3,respectively.The monthly average C d only varied by 8% while the variation of C h was 18%,which reflects the different impacts of dead vegetation on momentum and heat transfer at this natural grassland.Moreover,with the removal of vegetation cover,grazing intensities reduced z 0m,z 0h,C d,and C h.     

Some evaluations of drag and bulk transfer coefficients over water bodies of different sizes

Three recent experiments allow evaluation of the bulk transfer coefficients for momentum, water vapour and sensible heat over water bodies of different sizes. As part of a study of evaporation rates from a swamp, measurements of latent and sensible heat fluxes were made over Lake Wyangan in southern N.S.W., Australia. This lake is of several kilometers diameter. In a later experiment, Reynolds stress and sensible heat transfer were measured from a natural-gas platform standing in Bass Strait, south of mainland Australia. The most recent experiment involved the direct measurement of each of these turbulent fluxes from a fixed tower erected in Lake Michigan, U.S.A.Perhaps the most important of the results is the finding that drag coefficients measured over Bass Strait are not significantly different from those over Lake Michigan, despite the obvious differences in depth, fetch, and hence surface wave structure. At both locations, drag coefficients are found to increase slightly with increasing wind speed, while at low wind speeds they are not significantly different from those corresponding to aerodynamic smoothness.Near-neutral bulk transfer coefficients for sensible heat and for water vapour are found to be similar. An average value of about 1.4 × 10^–3 is obtained.It is emphasized that stability effects should be considered in any discussion of drag coefficients or bulk transfer coefficients. Large errors can result if near-neutrality is incorrectly assumed.     

Turbulent characteristics and bulk transfer coefficients over the desert in the HEIFE area

Observations of surface-layer turbulence and turbulent fluxes were made over a desert in northwestern China as a part of HEIFE (HEIhe river Field Experiment). These show that the normalized variations of the vertical wind component and of the air temperature obey Monin-Obukhov similarity well, especially in free convective conditions. However, the variations of specific humidity do not obey Monin-Obukhov similarity.Mean bulk transfer coefficients of sensible heat and momentum flux are obtained as functions of stability over a wide stability range from the observed data of turbulent fluxes and mast profiles. However, the bulk transfer coefficient for water vapor could not be obtained because of the large scatter of the data. In free convective conditions, the sensible heat flux was found to be approximately proportional to the 1.4 power of temperature difference between the surface and 20m. The bulk transfer coefficient of sensible heat is also obtained as a function of the bulk Richardson number for practical convenience.     

Stability dependence of fluxes and bulk transfer coefficients in a tropical boundary layer

Turbulence data obtained aboard a NOAA P-3 research aircraft during flights over the eastern equatorial Pacific Ocean are used to obtain mean vertical profiles of water vapor density, potential temperature, wind speed and fluxes of latent heat, buoyancy and momentum. The variation of eddy fluxes and bulk transfer coefficients as a function of atmospheric stability are plotted for two of the flights. The observed transfer coefficients generally agree with those obtained from parameterizations based on surface-layer similarity theory (Deardorff, 1968; Kondo, 1975).