黄土高原半干旱雨养农田空气动力和热力参数分析

利用甘肃省定西干旱气象与生态环境试验基地2003年夏季加强观测期间的资料,计算动量粗燥长度、热量粗糙长度和热量输送附加阻抗,结合卫星反演的差值植被指数Indv和表面温度Ts将其推广到中国西北区东部,可用于计算非均匀地表能量通量。     

峨眉山地区近地层微气象特征研究

基于2019年12月至2020年11月峨眉山站梯度塔资料、辐射观测资料和地表通量资料,采用涡动相关法对峨眉山地区近地层的地表通量和蒸散发量的变化进行分析,并估算了零平面位移、空气动力粗糙度、空气热力粗糙度、动量通量输送系数和感热通量输送系数等重要的空气动力学和热力学参数.研究表明:近地面风速呈现高层高、低层低的特征,且...     

半干旱区不同下垫面近地层湍流通量特征分析

本文分析了2003～2005年半干旱区退化草地和农田下垫面近地层湍流通量日、季、年的变化特征, 探讨了不同年份的气候背景和下垫面土地覆被对地气交换过程的影响。结果表明: 半干旱区退化草地和农田近地层湍流通量具有明显的日变化、季变化周期; 地气间通量交换年际间的差异主要受当年的气候背景影响, 尤其是降水的影响; 同时还受到下垫面覆被的影响。潜热通量和感热通量的能量分配比率呈反位相变化, 且农田和退化草地的变化趋势相似, 在夏季潜热通量所占比例均超过感热通量; 两种下垫面的波恩比月均值变化趋势十分相似, 量级接近, 夏季低, 春、秋季高; 夏季退化草地和农田下垫面波恩比均小于或等于1。     

Turbulence Characteristics of the Stable Boundary Layer Over a Mid-Latitude Glacier. Part I: A Combination of Katabatic and Large-Scale Forcing

Profile and eddy-correlation (heights of 4 and 10 m) measurements performed on the Pasterze glacier (Austria) are used to study the characteristics of the stable boundary layer under conditions of katabatic and large-scale forcing. We consider cases where large-scale forcing results in a downslope (or following) ambient wind. The analysis of averaged spectra and cospectra reveals low frequency perturbations that have a large influence on the variances of temperature and horizontal wind components and also alter the cospectra of momentum and sensible heat flux. Only the spectrum of the vertical wind speed is comparable to universal spectra. The low frequency perturbations occur as brief intermittent events and result in downward entrainment of ambient air thereby producing enhanced downward sensible heat fluxes and downward as well as upward momentum fluxes with various magnitudes and timescales. After the variances were high pass filtered, the normalised standard deviations of wind speed and temperature compare favourably to findings in the literature within the range 0>z/L>0.5. For larger z/L they deviate as a result of an increased influence from low frequency perturbations and thus non-stationarity. In line with this, the turbulent kinetic energy budget (at 4 m height) indicates that production (shear) is in balance with destruction (buoyancy and dissipation) within the range 0>z/L>0.3. Non-dimensional gradients of wind speed within the range 0>z/L>0.3 have a slope of about 3.5. The scatter for the dimensionless temperature gradient is quite large, and the slope is comparable to that for wind speed gradients. For z/L>0.3 the imbalance in the turbulent kinetic energy budget grows and non-dimensional gradients for wind speed and temperature deviate considerably from accepted values as a result of increased non-stationarity. Average roughness lengths for momentum and sensible heat flux derived from wind speed and temperature profiles are respectively 1 × 10^-3 m and 6 × 10^-5 m, consistent with the literature. The ratio (z_0h/z_0m) compares to those predicted by surface renewal models. A variation of this ratio with the roughness Reynolds number is not indicated by our data.     

Numerical simulation of the impact of vegetation index on the interannual variation of summer precipitation in the Yellow River Basin

Two sets of numerical experiments using the coupled National Center for Environmental Prediction General Circulation Model （NCEP/GCM T42L18） and the Simplified Simple Biosphere land surface scheme （SSiB） were carried out to investigate the climate impacts of fractional vegetation cover （FVC） and leaf area index （LAI） on East Asia summer precipitation, especially in the Yellow River Basin （YRB）. One set employed prescribed FVC and LAI which have no interannual variations based on the climatology of vegetation distribution; the other with FVC and LAI derived from satellite observations of the International Satellite Land Surface Climate Project （ISLSCP） for 1987 and 1988. The simulations of the two experiments were compared to study the influence of FVC, LAI on summer precipitation interannual variation in the YRB. Compared with observations and the NCEP reanalysis data, the experiment that included both the effects of satellite-derived vegetation indexes and sea surface temperature （SST） produced better seasonal and interannual precipitation variations than the experiment with SST but no interannual variations in FVC and LAI, indicating that better representations of the vegetation index and its interannual variation may be important for climate prediction. The difference between 1987 and 1988 indicated that with the increase of FVC and LAI, especially around the YRB, surface albedo decreased, net surface radiation increased, and consequently local evaporation and precipitation intensified. Further more, surface sensible heat flux, surface temperature and its diurnal variation decreased around the YRB in response to more vegetation. The decrease of surface-emitting longwave radiation due to the cooler surface outweighed the decrease of surface solar radiation income with more cloud coverage, thus maintaining the positive anomaly of net surface radiation. Further study indicated that moisture flux variations associated with changes in the general circulation also contributed to the precipitation interannual variation.     

盘锦芦苇湿地空气动力学参数动态特征及其影响因素分析

应用盘锦芦苇生态系统观测场的涡度相关通量观测系统和小气候梯度系统的观测资料,估算了芦苇下垫面的空气动力学参数,并分析了其影响因素。结果表明:芦苇湿地零平面位移d和粗糙度Z0的季节变化总体呈现先增加后减少的单峰曲线变化规律。Z0和d均在9月达到最大,分别为0.24 m和1.85 m;12月达到最小,分别为0.03 m和0.02 m。芦苇湿地的Z0和d的季节变化主要受叶面积指数(LAI)、株高(h)及风速的影响。d随h的增加而单调增加,Z0随着h的变化遵循二次曲线,d/h、Z0/h与LAI之间的复相关系数分别为0.99和0.78。研究亦表明,大气稳定度和风向也对d和Z0有一定的影响。     

Heat Flux in the Coastal Zone

Various difficulties with application of Monin–Obukhov similarity theory are surveyed including the influence of growing waves, advection and internal boundary-layer development. These complications are normally important with offshore flow. The transfer coefficient for heat is computed from eddy correlation data taken at a mast two kilometres off the Danish coast in RASEX. For these coastal zone data, the thermal roughness length shows no well-defined relation to the momentum roughness length or roughness Reynolds number, in contrast to previous theories. The variation of the momentum roughness length is dominated by wave state. In contrast, the thermal roughness length shows significant dependence on wave state only for small values of wave age where the mixing is apparently enhanced by wave breaking. The development of thin internal boundary layers with offshore flow substantially reduces the heat transfer and thermal roughness length but has no obvious influence on momentum roughness length. A new formulation of the thermal roughness length based on the internal boundary-layer depth is calibrated to the RASEX data. For the very stable case, the turbulence is mainly detached from the surface and existing formulations do not apply.As an alternative to adjusting the thermal roughness length, the transfer coefficient is related directly to the stability and the internal boundary-layer depth. This avoids specification of roughness lengths resulting from the usual integration of the non-dimensional temperature function. The resulting stability function is simpler than previous ones and satisfies free convection similarity theory without introduction of the gustiness factor. The internal boundary layer also influences the moisture transfer coefficient.     

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。     

中国西北干旱区戈壁下垫面夏季的热力输送

以敦煌戈壁站2004年6月和2008年8月的常规观测和超声观测为例,分析了西北干旱区戈壁下垫面夏季热力输送的一般过程及特征。首先评价了湍流通量的观测质量以及仪器观测的地表能量通量闭合问题,结果表明敦煌戈壁站的观测在白天总体较好。夏季地表能量通量的平均日变化显示,潜热通量整天都很小,可以忽略,白天到达地表的短波辐射以及地表向上的长波辐射非常强,地表净辐射主要转化为感热输送（敦煌戈壁站在中午时平均分别达380W·m-2以上和250W·m-2以上）;夜间土壤释放热量以平衡地表的辐射冷却,感热通量略低于0。白天时地表大气经常触发自由对流活动,影响动量通量的观测质量,并有效输送地表热力至上层大气中,有助于形成超厚大气边界层。分析了戈壁下垫面的动量粗糙度特征和热力粗糙度特征（敦煌戈壁站动量粗糙度约为0．6mm）,热力粗糙度基本小于动量粗糙度一个量级,这符合目前对干旱区戈壁下垫面热力输送特征的初步认识。     

Analysis of the variability of canopy resistance over a desert steppe site in Inner Mongolia,China

ABSTRACT Canopy resistance substantially affects the partitioning of available energy over vegetated surfaces. This study analyzed the variability of canopy resistance and associated driving environmental factors over a desert steppe site in Inner Mongolia, China, through the use of eddy-flux and meteorological data collected from 2008 to 2010. Distinct seasonal and interannual variabilities in canopy resistance were identified within those three years, and these variabilities were controlled primarily by precipitation. Strong interannual variability was found in vapor pressure deficit （VPD）, similar to that of air temperature. Based on the principal component regression method, the analysis of the relative contribution of five major environmental factors [soil-water content （SWC）, leaf-area index （LAI）, photosynthetically active radiation （Kp）, VPD, and air temperature] to canopy resistance showed that the canopy-resistance variation was most responsive to SWC （with 〉 35% contribution）, followed by LAI, especially for water-stressed soil conditions （〉 20% influence）, and VPD （consistently with an influence of approximately 20%）. Canopy-resistance variations did not respond to Kp due to the small interannual variability in Kp during the three years. These analyses were used to develop a new exponential function of water stress for the widely used Jarvis scheme, which substantially improved the calculation of canopy resistance and latent heat fluxes, especially for moist and wet soils, and effectively reduced the high bias in evaporation estimated by the original Jarvis scheme. This study highlighted the important control of canopy resistance on plant evaporation and growth for the investigated desert steppe site with a relatively low LA1.     

1998年南海季风爆发期间近海面层大气湍流结构和通量输送的观测研究

1998年5月14日至6月22日,在西沙永兴岛近海铁塔上进行了一次海-气通量观测试验,观测期包括了西南季风爆发前、爆发、爆发后风速加强等几个阶段。这次试验获得该年西南季风爆发的天气特征以及由涡度相关法、廓线法计算的动量、感热、潜热通量及湍流强度等一些统计量分布。分析结果表明,观测期湍流强度σu、σv、σw与平均风速之比为0.096、0.066、0.045;在近中性条件下（z/L≈0）,各相似函数基本为常数,σu/u＊≈3,σv/u＊≈2,σw/u＊≈1.25;在稳定条件下u、v、w三方向σ/u＊近似相等;在稳定与不稳定条件下σt/t＊随稳定度参数z/L的变化趋势相似,但符号相反。摩擦速度u＊随风速的变化接近于关系式u＊=0.029U10+0.006（U10为10m高度30min平均风速）,空气动力粗糙度长度z0变化在0.01～0.35mm之间。观测期动量通量变化在0.05～0.30N/m2之间,季风爆发期明显增大;曳力系数CD平均为1.12×10-3,它随平均风速变化可以表示为关系式103CD=0.003U210+0.020U10+0.836或103CD=0.056U10+0.732。感热通量由海洋输向大气,平均值为7.8W/m2,数值在0～15W/m2之间变化,季风爆发后明显增大;潜热通量数值一般变化于50～200W/m2,白天中午数值较高,夜间较低。季风爆发后也明显增大。观测期间鲍恩比（BowenRatio）日平均为0.05左右。     

SPATIO-TEMPORAL VARIATION OF SENSIBLE HEAT FLUX OVER SOUTHERN CHINA

The spatio-temporal variation of surface sensible heat flux (SHF) in southern China (SC) is studied based on the data evaluated from conventional observational meteorological data. There exist prominent increasing trends in all seasonal surface sensible heat fluxes in the western SC and decreasing trends in the central-eastern part of southern China. The variations of surface sensible heat flux in all seasons are dominant on interannual time-scales. The land-air temperature difference and the near-surface wind speed are two key factors for the interannual variations of SHF, but the former is more important. The first two major anomalous patterns of SHF are presented as the region-wide in-phase anomalies and the east-west dipole anomalies, respectively, based on the EOF analysis results.     

TEST OF A SENSIBLE HEAT FLUX – RADIOMETRIC SURFACE TEMPERATURE RELATIONSHIP FOR HAPEX-SAHEL

The estimation of the sensible heatflux from thermal infrared temperature requires anestimate of the excess resistance to be added to theaerodynamic resistance to the transfer of heat fromthe surface. This excess resistance can be expressedin terms of kB-1. An earlier studysuggested that the sensible heat flux over semi-aridregions could be derived from satellite thermalinfrared temperature using a value of kB-1= 7. Values of kB-1 were derived frommeasurements of sensible heat flux, radiometricsurface temperature, air temperature and wind speedtaken over millet, savannah and open forest sitesduring HAPEX-Sahel. These were comparable to valuesderived over similar sites during a previous study. Sensible and latent heat fluxes were estimated usingno excess resistance, kB-1 = 7 andkB-1 set to the values derived from theHAPEX-Sahel data set. There was an improvement on theestimated fluxes when an excess resistance wasincorporated. However, there was no apparentdifference between the errors in the estimated fluxeswith kB-1 set to either the derived orfixed values. This provides additional support forthe use of kB-1 = 7 in the derivation ofsurface fluxes from satellite data for sparsecanopies.     

青藏高原近地层通量特征的合成分析

利用中日亚洲季风机制合作研究计划 ,设置在青藏高原东部地区的拉萨、日喀则、那曲和林芝 4地 1993年 7月～ 1999年 3月近 7a的自动气象站 (AWS)近地层梯度观测资料 ,确定出分季节的高原地表粗糙度和逐日的地面总体输送系数 ,以此为基础用总体输送公式对地面动量、感热和潜热通量进行了计算 ,并用合成方法分析了 1993～1999年高原近地层通量夏季、冬季的日变化和月变化特征     

Stability Dependence of Height Scales and Effective Roughness Lengths of Momentum and Heat Transfer Over Roughness Changes

It is widely accepted that the correct formulation of an effective roughness length, defined as the area average of the roughness length in heterogeneous terrain, relies upon the appropriate de-termination of a height scale. At this height a meteorological quantity is approximately in equilibrium with local surface conditions and independent of horizontal position. This research note determines explicitly the different height scales from the perturbation solutions of flow velocity and temperature, as well as the fluxes of momentum and heat, in a stratified boundary layer. These solutions are derived from the asymptotic approximation theory and shown to capture major characteristics of momentum and heat transfer over heterogeneous terrain with changes of the underlying roughness lengths. The effective roughness lengths can then be computed by use of these height scales. The dependence of height scales and effective roughness lengths upon stratification is also discussed briefly.     

Heat and mass transfer to and from surfaces with dense vegetation or similar permeable roughness

A differential equation is obtained to describe the concentration of passive admixtures (water vapor, sensible heat, pollutants, CO₂, etc.) of turbulent flow inside a dense and uniform vegetational canopy. The profiles of eddy diffusivity, wind speed and shear stress are assumed to be exponential decay functions of depth below the top of the canopy. This equation is solved for the case of a vegetation with constant concentration of the admixture at the foliage surfaces. The solution is used to formulate bulk mass or heat transfer coefficients, which can be applied to practical problems involving surfaces covered with a vegetation or with similar porous or fibrous roughness elements. The results are shown to be consistent with experimental data presented by Chamberlain (1966), Garratt and Hicks (1973) and Garratt (1978). Calculations with the model illustrate that, as compared to its behavior over surfaces with bluff roughness elements, ln(z ₀/z _0c ) (wherez ₀ is the momentum roughness andz _0c , the scalar roughness) for permeable roughness elements is relatively insensitive tou _* and practically independent ofz ₀.     

城市表面粗糙度长度的确定

讨论了动量粗糙度长度与热量和水汽等标量粗糙度长度在形式上和物理本质上的不同，以及造成这些不同的原因和条件，分析了决定动量粗糙度的几种因素，并给出了确定动量粗糙度长度的简化关系式，并且根据城市冠层与其上惯性次层能量和动量守衡的原因，建立了热量和水汽粗糙度与动量粗糙度之间的联系，得到了确定热量和水汽粗糙度长度的简化关系式，最后，通过数值试验，表明了动量粗糙度和标量粗糙度变化特征以及对一些主要参数的敏感程度，以及动量粗糙度与标量粗糙度的动态关系。     

An Improvement of the Louis Scheme for the Surface Layer in an Atmospheric Modelling System

The Louis scheme for calculating the vertical eddy fluxes within the atmospheric surface layer is improved by broadening the original assumptions. In our approach, the momentum and heat transfer roughness lengths (z₀ and z_T respectively) can be different, and z₀ need not be negligibly small compared with the lowest height (z) in modelling. For these conditions, we choose more consistent wind and potential temperature profile forms, then derive new algorithms for calculating fluxes. Improvement is demonstrated for a wide range of z/L (L is the Obukhov length), z/z₀ and z₀ z_T, by comparing these fluxes with those derived from a theoretical surface-layer model. The improved algorithms can be used in atmospheric modelling systems for more varied surfaces and a wide range of atmospheric stability.     

卫星遥感结合气象资料计算的青藏高原地面感热特征分析

本文选取1981年7月至2012年12月美国国家航空和航天局（NASA）制作的归一化的动态植被指数（NDVI）资料、根据NDVI值计算地表热力输送系数（C_H）的参数化关系式（C_H-I_NDV）和青藏高原70个常规气象观测资料,计算了青藏高原全区的逐月地表热力输送系数（C_H）,讨论了其时空分布特征,并在此基础上计算了高原70个常规台站的感热通量（SSHF）序列,并与已有感热资料进行了对比。随后,探讨了地面感热通量的气候特征及其年际变化与气候因子的关系。结果表明:高原地区的C_H值具有明显的空间差异和季节差异,表现为东高西低、夏季大、冬季小的特点。感热的年际变化在冬季主要响应于地气温差的变化,夏季则受地面风速影响较大;由于风速减小趋缓,地气温差增大,变化趋势在2003年前后由减弱趋势转变为增强趋势,这种趋势的转变最早发生在2001年秋季,且在高原全区具有较好的一致性。     

Heat and Mass Transfer to and from Surfaces with Dense Vegetation or Similar Permeable Roughness

A differential equation is obtained to describe the concentration of passive admixtures (water vapor, sensible heat, pollutants, CO₂, etc.) of turbulent flow inside a dense and uniform vegetational canopy. The profiles of eddy diffusivity, wind speed and shear stress are assumed to be exponential decay functions of depth below the top of the canopy. This equation is solved for the case of a vegetation with constant concentration of the admixture at the foliage surfaces. The solution is used to formulate bulk mass or heat transfer coefficients, which can be applied to practical problems involving surfaces covered with a vegetation or with similar porous or fibrous roughness elements. The results are shown to be consistent with experimental data presented by Chamberlain (1966), Garratt and Hicks (1973) and Garratt (1978). Calculations with the model illustrate that, as compared to its behavior over surfaces with bluff roughness elements, ln(z ₀/ z _oc ) (where z ₀ is the momentum roughness and Z _oc the scalar roughness) for permeable roughness elements is relatively insensitive to u _* and practically independent of z ₀.