Attenuation of Scalar Fluxes Measured with Spatially-displaced Sensors   总被引：1，自引：0，他引：1  

T. W. Horst  D. H. Lenschow 《Boundary-Layer Meteorology》2009,130(2):275-300

Observations from the Horizontal Array Turbulence Study (HATS) field program are used to examine the attenuation of measured scalar fluxes caused by spatial separation between the vertical velocity and scalar sensors. The HATS data show that flux attenuation for streamwise, crosswind, and vertical sensor displacements are each a function of a dimensionless, stability-dependent parameter n _m multiplied by the ratio of sensor displacement to measurement height. The scalar flux decays more rapidly with crosswind displacements than for streamwise displacements and decays more rapidly for stable stratification than for unstable stratification. The cospectral flux attenuation model of Kristensen et al. agrees well with the HATS data for streamwise sensor displacements, although it is necessary to include a neglected quadrature spectrum term to explain the observation that flux attenuation is often less with the scalar sensor downwind of the anemometer than for the opposite configuration. A simpler exponential decay model provides good estimates for crosswind sensor displacements, as well as for streamwise sensor displacements with stable stratification. A model similar to that of Lee and Black correctly predicts flux attenuation for a combination of streamwise and crosswind displacements, i.e. as a function of wind direction relative to the sensor displacement. The HATS data for vertical sensor displacements extend the near-neutral results of Kristensen et al. to diabatic stratification and confirm their finding that flux attenuation is less with the scalar sensor located below the anemometer than if the scalar sensor is displaced an equal distance either horizontally or above the anemometer.  相似文献   

Assessing Tower Flux Footprint Climatology and Scaling Between Remotely Sensed and Eddy Covariance Measurements   总被引：2，自引：1，他引：1  

Baozhang?Chen  T.?Andrew?Black  Nicholas?C.?Coops  Thomas?Hilker  J.?A.? Trofymow  Kai?Morgenstern 《Boundary-Layer Meteorology》2009,130(2):137-167

We describe pragmatic and reliable methods to examine the influence of patch-scale heterogeneities on the uncertainty in long-term eddy-covariance (EC) carbon flux data and to scale between the carbon flux estimates derived from land surface optical remote sensing and directly derived from EC flux measurements on the basis of the assessment of footprint climatology. Three different aged Douglas-fir stands with EC flux towers located on Vancouver Island and part of the Fluxnet Canada Research Network were selected. Monthly, annual and interannual footprint climatologies, unweighted or weighted by carbon fluxes, were produced by a simple model based on an analytical solution of the Eulerian advection-diffusion equation. The dimensions and orientation of the flux footprint depended on the height of the measurement, surface roughness length, wind speed and direction, and atmospheric stability. The weighted footprint climatology varied with the different carbon flux components and was asymmetrically distributed around the tower, and its size and spatial structure significantly varied monthly, seasonally and inter-annually. Gross primary productivity (GPP) maps at 10-m resolution were produced using a tower-mounted multi-angular spectroradiometer, combined with the canopy structural information derived from airborne laser scanning (Lidar) data. The horizontal arrays of footprint climatology were superimposed on the 10-m-resolution GPP maps. Monthly and annual uncertainties in EC flux caused by variations in footprint climatology of the 59-year-old Douglas-fir stand were estimated to be approximately 15–20% based on a comparison of GPP estimates derived from EC and remote sensing measurements, and on sensor location bias analysis. The footprint-variation-induced uncertainty in long-term EC flux measurements was mainly dependent on the site spatial heterogeneity. The bias in carbon flux estimates using spatially-explicit ecological models or tower-based remote sensing at finer scales can be estimated by comparing the footprint-weighted and EC-derived flux estimates. This bias is useful for model parameter optimizing. The optimization of parameters in remote-sensing algorithms or ecosystem models using satellite data will, in turn, increase the accuracy in the upscaled regional carbon flux estimation.  相似文献   

2008年夏季风期间西沙海域海-气通量交换及热量收支     

黄磊  王长科  闫俊岳  孙启振  姚华栋  赵学华  陈长丘 《气象学报》2012,70(3):492-505

2008年4—10月在中国南海西沙永兴岛近海进行了第4次海-气通量观测试验,获得了整个夏季风期间近海面层湍流脉动量及辐射、表层水温、波浪及距水面3.5、7.0、10.5m高度温、湿、风梯度观测资料,根据涡动相关法和COARE3.0法计算结果研究了2008年南海西南季风爆发、发展、中断、衰退包括暴雨、台风、冷空气影响等天气过程中海-气通量交换和热量收支变化。结果表明:(1)季风爆发前的晴天太阳总辐射强,而海洋失热量较小,热量净收支为较大正值,海面温度迅速升高。季风爆发期太阳总辐射仍然较强,大气长波辐射也有所增强,而海面长波辐射变化很小,故海面净辐射收支仍为正值;(2)季风活跃期特别是降水阶段感热通量增大,季风中断阶段变小;季风活跃期虽然潜热通量增大,由于太阳短波辐射没有减少,海洋净热量收支稍有盈余;中断阶段潜热通量、感热通量减少,海洋吸热大于季风活跃期;降水阶段由于太阳短波辐射减小,感热通量增大,海洋热量收支出现较大负值,海面温度很快降低。季风衰退期风力减弱,湿度减小,潜热通量减小,海洋热量收入又出现较大正值,海面温度回升;(3)台风影响过程中潜热通量随着风速增强迅速增大;感热通量因降水情况不同而有差异,晴天时减小,大雨时剧烈增大;由于太阳短波辐射减少、潜热通量剧增,海洋热量净收支出现负值,促使海面温度迅速降低;(4)动量通量主要与海表面风速有关;动量通量τ与风速V的关系可以表示为τ=0.00171v~2-0.003809v+0.02213。  相似文献   

汶川M_s 8.0地震破裂带CO_2、CH_4、Rn和Hg脱气强度     

周晓成  孙凤霞  陈志  吕超甲  李静  仵柯田  杜建国 《岩石学报》2017,33(1):291-303

地震活动断裂带能够向大气释放大量的温室气体、放射性气体和有毒气体(CO_2、CH_4、Rn和Hg),并对大气环境的影响产生复杂的影响。利用静态暗箱法,对汶川M_s8.0地震破裂带CO_2、Rn和Hg脱气强度进行实地测量,并计算了CO_2和Hg脱气对大气的年贡献量。结果表明:(1)破裂带土壤气中CO_2、CH_4、Rn和Hg异常浓度最大值分别可以达到7.98%、2.38%、524.30k Bq/m~3和161.00ng/m~3;破裂带CO_2、Rn和Hg脱气平均通量是34.95g·m~(-2)d~(-1)、36.11m Bq·m~(-2)s~(-1)和26.56ng·m~(-2)h~(-1),最大值分别达到259.23g·m~(-2)d~(-1)、580.35m Bq·m~(-2)s~(-1)和387.67ng·m~(-2)h~(-1);(2)汶川Ms8.0地震破裂带向大气脱气的CO_2年贡献量是0.95Mt,Hg的年贡献量是15.94kg。汶川Ms8.0地震破裂带破裂CO_2、CH_4、Rn和Hg等的脱气强度,不仅与破裂带渗透率有关,还与断裂带浅部存在的气藏、煤层以及磷矿层等气体源有重要的联系。  相似文献   

依据地震活动资料研究龙陵—澜沧地震带分段   总被引：1，自引：0，他引：1  

周真恒  周瑞琦  向才英 《云南地质》2001,20(2):203-210

根据地震活动的空间分布、强震的震害影响场及构造能流图象分析结果，提出了龙陵－澜沧构造带的分段结果，并通过带内地震迁移规律，对1988年耿马7．2级地震后未来地震活动趋势作了初步估计：永德及北西地区和澜沧及其南东地区存在发生7级及7级以上地震的可能性，下次大震可能将发生于永德地区或其北西更远的地区。  相似文献   

夏季风期间南海南部海区海-气通量交换浅析     

林锡贵 《广东气象》2003,(2):5-7

海洋考察资料分析表明，夏季风期间南海南部海区海洋输向大气的热通量倍增，热通量的增、减过程与对流天气密切相关，季风潮天气过程中的热通量值居各天气过程之首，某些时段感热通量会出现大气向海洋的反向输送过程，地理环境使同一天气过程影响下海区内各通量的水平分布明显不均，海洋输向大气的热通量明显影响500hPa以下各层大气。  相似文献   

Characteristics of low frequency oscillations of the atmosphere-ocean coupling     

Randhir Singh  B. Simon  P. C. Joshi 《Journal of Earth System Science》2002,111(4):413-423

The low frequency oscillation of latent heat flux over the tropical oceans has been studied. The NCEP reanalyzed fields of wind and humidity alongwith Reynolds SST are used to compute the instantaneous as well as monthly mean surface latent heat fluxes (LHF) for the year 1999. The procedure of LHF computation is based on bulk method. Spectral analysis shows that significant energy is contained in Madden Julian Oscillation band in the winds, SST, moisture and in the latent heat flux. The global distribution of wind, humidity, SST and LHF oscillation on the time scale of 30–50 days are analyzed. Maximum amplitude of oscillation on this time scale in all the above mentioned parameters were found over the Indian Ocean. The fluctuation of surface wind speed and moisture controls the latent heat flux on this time scale. The fluctuation of SST on this time scale does not seem to be important over most of the oceans.  相似文献   

DERIVATION OF FLUXES FROM PROFILES OVER A MODERATELY HOMOGENEOUS FOREST     

FRED C. BOSVELD 《Boundary-Layer Meteorology》1997,84(2):289-327

Measurements of fluxes and profiles of wind andtemperature are performed in the roughness layer ofa moderately homogeneous forest location. Weinvestigate to what extent vertical scalar fluxescan be derived from profile measurements. Theinfluence of inhomogeneities in the upwind terrainis investigated with footprint analysis and with aninhomogeneous surface-layer model. Four methods toestimate displacement height are suggested, amongthem is a method involving the structure parameterof the vertical wind. All methods give a decrease ofdisplacement height with increasing wind speed,while roughness length is found to increase withincreasing wind speed. For near-neutral conditionsdimensionless temperature gradients are found to besubstantially lower than the surface-layer valuesfound in the literature for homogeneous terrain with lowvegetation. Dimensionless shear however iscomparable with the surface-layer value. The heightof the roughness layer is 20 times the roughnesslength. Two schemes with locally derived surfaceparameters are tested to derive friction velocityand sensible heat flux from the profilemeasurements. These site specific schemes performsatisfactorily. A third scheme based on surface parameters chosen a priorifrom the literatureperforms significantly worse especially for low windspeed and unstable cases.  相似文献   

High-resolution numerical simulations of Hurricane Isabel (2003) over North Carolina     

Peter Childs  Sethu Raman  Ryan Boyles 《Natural Hazards》2007,41(3):401-411

Two numerical simulations were performed to study the ability of a high-resolution mesoscale model to predict the track and structure of Hurricane Isabel over North Carolina. One simulation (Control) used standard NCEP climatologically-based sea surface temperature (SST) data for the lower boundary condition while another simulation (Experimental) prescribed real-time high-resolution SST data for the lower boundary. Results from this study show that both simulations predict the track of Isabel over North Carolina reasonably well, although the track predicted by the experimental simulation agrees more closely with observations. The experimental simulation more closely agrees with observations of the intensity of Isabel and the amount and spatial distribution of precipitation. These results reinforce the importance of accurate high-resolution SST data on numerical simulations of tropical cyclones.  相似文献   

The correct form of the Webb,Pearman and Leuning equation for eddy fluxes of trace gases in steady and non-steady state,horizontally homogeneous flows   总被引：1，自引：0，他引：1  

Ray Leuning 《Boundary-Layer Meteorology》2007,123(2):263-267

The original density corrections proposed by Webb et al. [Webb EK, Pearman GI, Leuning R (1980) Quart J Roy Meteorol Soc 106:85–100] for calculating the eddy fluxes of trace gases are shown to be correct for both steady and non-steady state, horizontally homogeneous flows. The revised theory replaces the original assumption of zero vertical flux of dry air with the requirement of no sources or sinks of dry air in the layer below the height of measurement.  相似文献