Comparison of Ozone Fluxes over a Maize Field Measured with Gradient Methods and the Eddy Covariance Technique     

Zhilin ZHU  Xinzhai TANG  Fenghua ZHAO 《大气科学进展》2020,37(6):586-596

Ozone(O_3) fluxes were measured over a maize field using the eddy covariance(EC) technique and gradient methods.The main objective was to evaluate the performance of the gradient methods for measuring the O_3 flux by comparing them with the EC O_3 flux.In this study,turbulent exchange coefficients(K) calculated with three methods were compared.These methods were the aerodynamic gradient(AG) method(in which K is calculated by using wind speed and temperature gradients),the aerodynamic gradient combined with EC(AGEC) method,in which the friction velocity and other variables are based on EC measurements,and the modified Bowen ratio using the EC sensible heat flux and temperature gradient(MBR) method.Meanwhile,the effects of the measurement and calculation methods of the O_3 concentration gradient were analyzed.The results showed that:(1) on average,the transfer coefficient computed by the MBR method was 40% lower,and the coefficient determined with the AG method was 25% higher,than that determined with the AGEC method.(2) The gradient method's O_3 fluxes with the MBR,AGEC,and AG methods were 30.4% lower,11.7% higher,and 45.6% higher than the EC O_3 flux,respectively.(3) The effect of asynchronous O_3 concentration measurements on the O_3 gradient must be eliminated when using one analyzer to cyclically measure two-level O_3 concentrations.The accuracy of gradient methods for O_3 flux is related to the exchange coefficient calculation method,and its precision mainly depends on the quality of the O_3 gradient.  相似文献   

土壤热传导方程解析解和那曲地区土壤热扩散率研究   总被引：6，自引：1，他引：6  

高志球  卞林根  张雅斌  王金星  姜冬梅 《气象学报》2002,60(3):352-360

文中用Laplace变换推导了土壤热传导方程的解析解和包含热对流项的土壤热传导方程的解析解。用青藏高原 8个土壤湿度、温度廓线观测站 1998年 9月 4日到 10日实测资料基础上 ,根据谐波方法和Laplace变换方法得到了土壤热传导方程的解析解 ,计算了这些站的总体土壤热扩散率 ;用包含热对流项的土壤热传导方程的解析解计算了土壤热扩散率。结果表明 :对于一个深度从 0 .0 4～ 0 .2 0m的浅薄土壤层 ,总体土壤热扩散率的值为 0 .30×10 -6～ 0 .98× 10 -6m2 /s,土壤热扩散率的值为 0 .15× 10 -6～ 0 .72× 10 -6m2 /s。由谐波方法得到的总体土壤热扩散率比由Laplace变换的值稍大 ;总体土壤热扩散率总是比土壤热扩散率大  相似文献   

块石的热扩散系数和导热系数确定方法   总被引：9，自引：3，他引：9  

孙斌祥  徐敩祖  赖远明  李东庆 《冰川冻土》2002,24(6):790-795

采用块石路堤、护坡有利于冻土地区路基的稳定性.基于气温波动条件下块石内部的温度波动幅度按指数规律衰减, 介绍了块石的热扩散系数和导热系数测量方法.实验中, 采用封闭的块石试样筒, 通过顶板温度波动的控制来模拟气温的周期性变化, 整个试样筒用绝热性能良好的海棉包扎, 使其侧向、底板绝热. 对粒径为6～8 cm, 4～6 cm, 2～4 cm的3种块石试样进行了具体测量, 由曲线拟合所得的结果具有较好的一致性.分析显示粒径较小的块石其热扩散系数和导热系数也较小.  相似文献   

Simulation of Meteorological Fields Within and Above Urban and Rural Canopies with a Mesoscale Model   总被引：3，自引：4，他引：3  

Sylvain Dupont  Tanya L. Otte  Jason K. S. Ching 《Boundary-Layer Meteorology》2004,113(1):111-158

Accurate simulation of air quality at neighbourhood scales (on order of 1-km horizontal grid spacing) requires detailed meteorological fields inside the roughness sub-layer (RSL). Since the assumptions of the roughness approach, used by most of the mesoscale models, are unsatisfactory at this scale, a detailed urban and rural canopy parameterisation, called DA-SM2-U, is developed inside the Penn State/NCAR Mesoscale Model (MM5) to simulate the meteorological fields within and above the urban and rural canopies. DA-SM2-U uses the drag-force approach to represent the dynamic and turbulent effects of the buildings and vegetation, and a modified version of the soil model SM2-U, called SM2-U(3D), to represent the thermodynamic effects of the canopy elements. The turbulence length scale is also modified inside the canopies. SM2-U(3D) assesses the sensible and latent heat fluxes from rural and urban surfaces in each of the computational layers inside the canopies by considering the shadowing effect, the radiative trapping by the street canyons, and the storage heat flux by the artificial surfaces. DA-SM2-U is tested during one simulated day above the city of Philadelphia, U.S.A. It is shown that DA-SM2-U is capable of simulating the important features observed in the urban and rural RSL, as seen in the vertical profiles of the shear stress, turbulent kinetic energy budget components, eddy diffusivity, potential air temperature, and specific humidity. Within the canopies, DA-SM2-U simulates the decrease of the wind speed inside the dense canopies, the skirting of the flow around the canopy blocks, warmer air inside the vegetation canopy than above open areas during the night and conversely during the day, and constantly warmer air inside the urban canopy. The comparison with measurements shows that the surface air temperature above rural and urban areas is better simulated by DA-SM2-U than by the `standard version' of MM5.  相似文献   

Hydro-thermal performance of unsaturated bentonite-sand buffer material     

R.N. Yong  A.M.O. Mohamed  I. Shooshpasha  C. Onofrei 《Engineering Geology》1997,47(4):51-365

Several series of one-dimensional heat and moisture flow tests were performed to examine the moisture and temperature distributions in the buffer material compacted to a dry density of 1.67 Mg m⁻³ and water content of 17.7%. In all tests, water was allowed to infiltrate into a horizontal soil column from one end under a constant hydrostatic head of 276 kPa. Also the specimens were heated from the other end by the heater to a constant temperature.

It is experimentally demonstrated that the moisture moves from both ends toward the mid part of the soil column due to both thermal gradient from one end and hydraulic gradient from the other end. It was observed that, in spite of no overall volume change, local volume change occurs in the system. The measured temperatures along the length of the specimen indicate that temperature distributions stabilize within a short period of time. The time required for the temperature to stabilize decreases as the heater skin temperature increases.

The diffusivity parameters are calculated using the measured moisture and temperature profiles combined with the finite difference method. Powell's optimization algorithm was used to determine the material parameters. Good agreements between experimentally measured and calibrated volumetric water content shows that the diffusion parameters can be expressed in a linear function of the volumetric water content and temperature.  相似文献   

浅层测温中几个重要干扰因素的分析及校正     

徐建华 《地球科学》1988,(3)

为了获取较多的来源于地球深部热源的温度信息,在浅层土壤测温中,必须认真分析严重干扰地表浅层温度场分布的因素,力图通过正确的校正将其影响的幅度压低。文中分析了地表状况不同(不同土质、不同植被条件)对地表浅层温度场的影响,提出了几种校正方法并重点讨论了求热扩散系数的方法。  相似文献   

Thermal diffusivity of olivine under upper mantle conditions   总被引：1，自引：0，他引：1  

Tomoo Katsura 《Geophysical Journal International》1995,122(1):63-69

  相似文献   

Thermal diffusivity of garnets at high temperature     

Anne M. Hofmeister 《Physics and Chemistry of Minerals》2006,33(1):45-62

Thermal diffusivity (D) of garnets with diverse chemical compositions was measured using the laser-flash technique, which is accurate (±2%) and isolates the lattice component from direct radiative transfer. Temperatures ranged from ~290 to ~1,600 K (unless limited by melting). Seven synthetic (e.g., YAG, GGG) and 15 natural garnets with two types of ionic substitution [Ca₃(Fe,Al)₂Si₃O₁₂ and (Mg,Fe,Ca)₃Al₂Si₃O₁₂] and varying amounts of OH^- were examined. Cation substitution or hydroxyl incorporation lowers D from end-member values. Thermal diffusivity is constant once the temperature (T) exceeds a critical value (T _sat) of ~1,100 to 1,500 K. From ~290 K to T _sat, the measurements are best represented by 1/D=A+BT+CT ² where A, B, and C are constants. These constants vary little among diverse chemical compositions, suggesting that the oxygen sublattice controls heat transport. Higher order terms are needed only when T _sat is low, such as Ant Hill garnet wherein 1/D=0.049403+0.0032299T−2.3992T ²×10⁻⁶+6.0168T ³×10⁻¹⁰(1/D in s/mm²; T in K). The mean free path (λ, computed from D and sound velocities) is slightly larger than the lattice parameter above T _sat, in accord with phonon–phonon interactions requiring non-localized modes. At most temperatures, λ is nm-sized. Large values of λ are obtained by extrapolation to a few Kelvins, suggesting that boundary scattering can only be important at extremely cold temperatures. The observed behavior with T and chemical composition is consistent with the damped harmonic oscillator model. Phonon transport is best represented by inverse thermal diffusivity wherein 1/D goes as T ⁿ where n is between 1 and 3 up to ~200 K, depends on a quadratic or cubic polynomial at moderate T, but is constant above T _sat. The predicted and observed temperature response of 1/D mimics the well-known form for heat capacity, in that acoustic modes control heat transport near cryogenic temperatures, optic phonons dominate above ambient temperature, and a limit analogous to that of Dulong and Petit is reached at very high temperature, due to full population of discrete phonon states.  相似文献   

Simultaneous determination of thermal conductivity, thermal diffusivity and specific heat in sI methane hydrate     

W. F. Waite  L. A. Stern  S. H. Kirby  W. J. Winters  D. H. Mason 《Geophysical Journal International》2007,169(2):767-774

Thermal conductivity, thermal diffusivity and specific heat of sI methane hydrate were measured as functions of temperature and pressure using a needle probe technique. The temperature dependence was measured between −20°C and 17°C at 31.5 MPa. The pressure dependence was measured between 31.5 and 102 MPa at 14.4°C. Only weak temperature and pressure dependencies were observed. Methane hydrate thermal conductivity differs from that of water by less than 10 per cent, too little to provide a sensitive measure of hydrate content in water-saturated systems. Thermal diffusivity of methane hydrate is more than twice that of water, however, and its specific heat is about half that of water. Thus, when drilling into or through hydrate-rich sediment, heat from the borehole can raise the formation temperature more than 20 per cent faster than if the formation's pore space contains only water. Thermal properties of methane hydrate should be considered in safety and economic assessments of hydrate-bearing sediment.  相似文献   

New analytical solution of the dispersion equation     

Khaled S.M. Essa  Soad M. Etman  M. Embaby 《Atmospheric Research》2007,84(4):337-344

The dispersion of pollutants from a point source is analytically investigated taking into consideration the vertical variation of both wind speed and eddy diffusivity. The deposition of the diffusing particles on the ground is taken into account throughout the boundary conditions. The concentration of pollutants under different atmospheric stabilities was found assuming that the vertical diffusion is limited by an elevated inversion layer. The decay distance of a pollutant along the wind direction for different atmospheric stabilities was derived. The resulting analytical formulae have been applied on a case study namely, the emission from the research reactor at Inshas. The results are discussed and presented in illustrative figures.  相似文献