从FY-4A卫星遥感数据和GFS资料估算全天空状况下的地表长波辐射通量

本文介绍一种利用FY-4A成像仪遥感数据和全球预报系统(GFS)资料估算全天空地表长波辐射通量的反演方法。该方法通过辐射传输模拟和统计回归计算建立云天地表下行长波辐射通量的反演模式,并基于GFS资料处理云覆盖地区的地表上、下行长波辐射通量。这种全天空状况下两种通量的反演结合了FY-4A晴空地表长波辐射业务产品和本文反演模式处理的云天地表上、下行长波辐射通量。2018年9月1日的处理结果与Aqua/CERES同类产品相对比,精度为:RMSE=20.52 W·m^-2,R=0.9481,Bias=3.3 W·m^-2(夜间地表下行辐射通量对比);RMSE=25.58 W·m^-2,R=0.9096,Bias=5.4 W·m^-2(白天地表下行辐射通量对比);RMSE=10.97 W·m^-2,R=0.9762,Bias=-3.3 W·m^-2(夜间地表上行辐射通量对比);RMSE=19.97 W·m^-2,R=0.9283,Bias=5.0 W·m^-2(白天地表上行辐射通量对比)。这些结果表明本文发展的方法能够反演出精度较好的云天上下行长波辐射通量资料,为今后利用FY-4后续星处理生成全天空状况下的地表长波辐射通量产品奠定了理论基础。     

从Himawari08卫星估算晴空地表长波辐射及其日变化特征初探

通过446183条全球晴空大气廓线的红外辐射传输模拟和统计回归,建立了由Himawari08成像仪通道遥测数据估算晴空地表上行、下行长波辐射通量的反演模式,模式应用于成像仪观测资料,处理出晴空地表上行、下行长波辐射通量实时产品,2016年2~6月的产品精度验证试验结果为:与相同时刻的AQUA卫星CERES仪器同类产品相比,地表上行通量均方根误差R_e=7.9 W/m2,相关系数R=0.9399,地表下行通量R_e=14.5 W/m2,R=0.9586;与由中国地面气象站地面气温和相对湿度观测经Brunt、Brutsaert经验公式计算的实时地表下行长波辐射通量相比,R_e=15.34 W/m2,R=0.8786;与用陆表温度计算的地表上行长波辐射通量相比,R_e=12.6 W/m2,R=0.9977。研究了2016年2、6月的晴空地表长波辐射产品,发现陆地晴空上、下行通量有着与太阳加热地表增温相应的明显日变化特征,峰值出现在12:00（当地时间,下同）至14:00,低谷出现在04:00至07:00,下行通量与上行通量几乎同步变化或约有延时,陆地上2个通量归一化的日变化指数类似一个半正弦曲线,而海面长波辐射通量则没有明显的日变化规律。     

青藏高原不同地区夏季近地层能量输送与微气象特征比较分析

利用2009年7月在青藏高原理塘、林芝、海北、拉萨获得的气象观测资料,对比分析了这些地区近地层气象要素、辐射收支及湍流通量日变化特征。结果表明:无论是高原东部、中部还是北部,无论是高原台地还是高山峡谷区,7月份近地层各气象要素、湍流通量、辐射收支都有明显的日变化。各地区的地表辐射、感热、潜热等最高值都出现在中午,最低值出现在早晨。地表反照率日变化均呈早晚高中午低的“U”型分布。地面热源强度在白天均为热源,正午为强热源,在夜间表现为弱的冷、热源交替出现。7月份近地层地气热量交换中,感热输送作用小,潜热输送占主导地位。动量通量和摩擦速度均在风速较大的下午较大,风速小的早晨小。      

Comparison between measured and modelled cloudless‐sky solar irradiances at the surface and at the top of the atmosphere

Abstract

Cloudless‐sky solar fluxes calculated by the radiative transfer algorithm used in the Canadian Climate Centre's general circulation climate model are compared with measurements of upwelling radiation at the top of the atmosphere (TOA) and downwelling radiation at the surface. The 12‐layer model partitions the solar spectrum into two broad wavebands (0.25–0.68 and 0.68–4.00 μm). The comparison utilized TOA fluxes estimated from Nimbus‐ 7 measurements and measured downwelling fluxes at the surface for Kalgoorlie, West Australia, and downwelling fluxes at the surface for Woodbridge, Ontario. Model estimates and measurements agreed to within experimental error for most solar zenith angles. Estimates improved, especially at Woodbridge, when aerosol effects were included. The mean bias error was less than 4% for surface irradiance and less than 6% for upwelling TOA irradiance, which produces a TOA albedo error of about 0.01.     

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。     

青藏高原大气—植被相互作用的模拟试验——Ⅰ.物理通量和参数

在原大气-植被相互作用模式AVIM的基础上作了改进，包括对值被生理过程，如（1）光合作用：（2）呼吸；（3）分配和（4）物候等新的描述方法。对青藏高原上30个站点进行模拟计算，给出了高压上地表辐射及水热物理通量以及地表拖曳系数和地面反照率的分布特征。模拟结果表明净辐射和感热通量由东南和西北增加，高原西北部地表反照率较高，东南部地表反照率较低。     

从FY-4静止气象卫星估算晴空地表下行长波辐射通量的反演模式

通过红外辐射传输模拟,计算了446183条全球晴空大气廓线的地表下行长波辐射通量以及FY-4成像仪通道亮温,应用统计回归分析模拟结果,建立了通道亮温与低层大气有效辐射温度的回归关系、大气柱总可降水量与低层大气比辐射率的回归关系,依据黑体辐射定律建立了由卫星观测估算地表下行长波辐射通量的反演模式。初步地,模式应用于FY-4成像仪代理资料Meteosat-8卫星的SEVIRI（Spring Enhanced Visible and Infared Imager）仪器观测数据,估算了2006年8月1日00:00（协调世界时,下同）、06:00、12:00、18:00地理范围在（45°S～45°N,45°W～45°E）的地表下行长波辐射通量,结果与用ECMWF 6 h预报场资料经验计算的通量相比,系统均方根误差（RMS）依次为12.1、13.0、20.7、12.5 W/m2,相关系数分别为0.9256、0.9291、0.9042、0.9325,相比于GOES-R同类产品（RMS=13.7 W/m2）,这一直接把卫星通道亮温与低层大气温度相联系的反演模式,其精度性能达到了应用研究对其反演产品的质量要求。     

不同土壤类型的热通量变化特征

利用2004—2007年中国科学院中国生态系统研究网络(CERN)生态站实测土壤热通量、辐射等资料,分析了不同土壤类型表层热通量的日变化和季节变化,以及不同土壤类型的热通量与总辐射、净辐射的关系。结果表明,由于导热率越大,热量传输就越快;热容量越小,热量传输也越快,造成土壤热通量的日较差和年较差较大,所以黄绵土和紫色土的表层热通量日较差最大(220～280 W.m-2),高寒草甸土和水稻土最小(55W.m-2);季节变化中土壤表层热通量的年较差变化范围在12～28W.m-2之间,灰漠土最大,为28W.m-2,热通量年较差从大到小依次为灰漠土、黄绵土、盐碱潮土、红壤土、紫色土、沼泽土、水稻土和高寒潮土,高寒潮土最小,为12W.m-2。不同土壤类型的热通量与总辐射、净辐射呈正相关关系,但不同土壤类型的土壤热通量在12:00(地方时)所占净辐射的比例各不相同,高寒草甸土最小,约为8%;黄绵土最大,为38%,多数土壤的热通量占净辐射的比例在15%～20%之间,这充分表明不同土壤类型表层热通量的传输存在很大差异。     

Climate response to introduction of the ESA CCI land cover data to the NCAR CESM

The European Space Agency Climate Change Initiative Land Cover data (ESA CCI-LC, from 1992 to 2015) is introduced to the National Center for Atmospheric Research Community Earth System Model version 1.2.1 (NCAR CESM1.2.1). In comparison with the original land surface data in the Community Land Model version 4 (ORG), the new data features notable land use and land cover change (LULCC) with increased forests over northeastern Asia and Alaska by decreasing shrublands and grasslands. Overestimated bare land cover over the Tibetan Plateau (TP) and the Rocky Mountains in the ORG are corrected with the replacements by grasslands and shrublands respectively in the new data. The model simulation results show that with the introduction of the ESA CCI-LC, the simulated surface albedo, surface net radiation flux, sensible and latent heat fluxes are relatively improved over the regions where significant LULCC exists, such as northeastern Asia, Alaska, the TP, and Australia. Surface air temperature, precipitation, and atmospheric circulation are improved in boreal winter but degraded in summer. The winter warming over northeastern Asia results from increased longwave downwelling flux and adiabatic heating while the notable winter cooling over Alaska is attributed to strong cold advection followed by reduced longwave downwelling flux. LULCC alters precipitation by influencing water vapor content. In winter, LULCC affects atmospheric circulation via modulating baroclinicity while in summer, it influences land-sea thermal contrast, thus affecting the intensity of East Asian summer monsoon. LULCC also alters the simulated dust burden.

     

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.     

The role of wintertime radiation in maintaining and destroying stable layers

Summary Strong stable layers are a common occurrence during western Colorado's winter. Analysis of radiosonde observations indicate wintertime boundary layer heights are near 500 m. The terrain in this region consists of mountains that rise approximately 1500–2000 m above the ground to the east, providing an effective blocking barrier. An experiment is described to observe upwelling and downwelling, longwave and shortwave radiative fluxes at two sites in western Colorado during January and February 1992, for combinations of clear, cloudy, snow covered, and bare ground periods. Analysis of the observations and the surface energy budget for typical Bowen ratios provides a better understanding of the role of radiation in maintaining and destroying stable layers.During the day, the surface received a net gain of energy from radiation, while at night there was a net loss. Over snow, the 24-hour net radiative flux was small and either positive or negative. Over bare soil, the 24-hour net radiative flux was positive but still small. There is little difference in the net radiative flux between clear and cloudy days; the reduction of the incident solar flux by clouds is nearly compensated by the hindering of the longwave cooling. The cumulative effects of the 24-hour net radiative flux were negative over snow early in the experiment. The 24-hour values shifted to near zero as the snow albedo decreased and were positive for bare ground.If the daytime net radiative flux is partitioned into sensible and latent heat flux using typical Bowen ratios, the daytime sensible heat available for destroying boundary layers is small for the low solar angles of the winter season. With a Bowen ratio of 0.5, the daytime sensible heat flux available is only 0.3 to 1.2 MJ m^–2 over a snow surface and 1.4 to 2.3 MJ m^–2 over soil. These heat fluxes will not build a deep enough boundary layer to break a typical wintertime inversion. The 24-hour sensible heat flux was negative at both sites for the entire experiment with this Bowen ratio.The radiation observations and the use of typical Bowen ratios lead to the conclusion that the net radiation will sustain or strengthen a stable atmosphere in the winter season in western Colorado. Analysis of the radiosonde observations confirm this result as the boundary layer depths were less than 500 m early in the experiment and grew to only 700 m later in the experiment.With 12 Figures     

Heat Flux Apportionment to Heterogeneous Surfaces Using Flux Footprint Analysis

Heat flux data collected from the Baiyangdian Heterogeneous Field Experiment were analyzed using the footprint method. High resolution (25 m) Landsat-5 satellite imaging was used to determine the land cover as one of four surface types: farmland, lake, wetland, or village. Data from two observation sites in September 2005 were used. One site (Wangjiazhai) was characterized by highly heterogeneous surfaces in the central area of the Baiyangdian: lake/wetland. The other site (Xiongxian) was on land with more uniform surface cover. An improved Eulerian analytical flux footprint model was used to determine "source areas" of the heat fluxes measured at towers located at each site from surrounding landscapes of mixed surface types.In relative terms results show that wetland and lake areas generally contributed most to the observed heat flux at Wangjiazhai, while farmland contributed most at Xiongxian. Given the areal distribution of surface type contributions, calculations were made to obtain the magnitudes of the heat flux from lake, wetland and farmland to the total observed flux and apportioned contributions of each surface type to the sensible and latent heat fluxes. Results show that on average the sensible heat flux from wetland and farmland were comparable over the diurnal cycle, while the latent heat flux from farmland was somewhat larger by about 30-50 W m-2 during daytime. The latent and sensible fluxes from the lake source in daytime were about 50 W m-2 and 100 W m-2 less, respectively, than from wetland and farmland. The results are judged reasonable and serve to demonstrate the potential for flux apportionment over heterogeneous surfaces.     

Simulation of the Bare Soil Surface Energy Balance at the Tongyu Reference Site in Semiarid Area of North China

The performance of a 1-D soil model in a semiarid area of North China was investigated using observational data from a cropland station at the Tongyu reference site of the Coordinated Enhanced Observing Period (CEOP) during the non-growing period, when the ground surface was covered with bare soil. Comparisons between simulated and observed soil surface energy balance components as well as soil temperatures and water contents were conducted to validate the soil model. Results show that the soil model could produce good simulations of soil surface temperature, net radiation flux and sensible heat flux against observed values with the RMSE of 1.54oC, 7.71 W m-2 and 27.79 W m-2, respectively. The simulated volumetric soil water content is close to the observed values at various depths with the maximal difference between them being 0.03. Simulated latent heat and ground heat fluxes have relatively lower errors in relative to net radiation and sensible heat flux. In conclusion, the soil model has good capacity to simulate the bare soil surface energy balance at the Tongyu cropland station and needs to be further tested in longer period and at more sites in semiarid areas.     

风云四号静止轨道气象卫星成像仪典型观测区域设计

风云四号气象卫星是我国新一代静止轨道气象卫星,采用三轴稳定姿态控制方式,极大地提高对地观测精度及观测频次,同时也对有效载荷观测模式的灵活设计提出了更高要求。星上装载的静止轨道辐射成像仪是我国静止轨道气象卫星携带的同类仪器中最为先进的。利用最先进的观测仪器,提高观测效率,在气象服务中发挥更大的作用是气象卫星应用的根本。深入探讨了风云四号静止轨道气象卫星成像仪的工作模式,首次针对不同的观测需求提出了灵活的成像仪观测区域设计方案,有效满足典型区域的不同观测需求,在成像仪在轨测试中发挥了重要作用,为开展业务运行奠定了坚实的基础。     

白洋淀地区非均匀大气边界层的综合观测研究——实验介绍及近地层微气象特征分析

介绍了国家自然科学基金重点项目 "地表通量参数化与大气边界层过程的基础研究" 在河北省白洋淀地区进行的两次综合观测实验(时间分别是2004年11月16～22日和2005年9月8～27日),这两次实验获得了大量宝贵的资料,全面深入的资料分析正在进行中.此文主要限于白洋淀地区水陆不均匀地表近地面层微气象特征的分析.结果表明: 陆地上近地面层的气温日变化比水域上的大,而风速比水域上的小,其中9月份陆地上白天的气温比水域上的高,夜间比水域上的低,11月份两地白天气温接近,但夜间陆地上的气温明显偏低; 无论是9月还是11月,水域上近地面层都是以下沉气流为主,而陆地则在中午前后存在弱的上升运动; 9月份,两地的近地面层短波射入辐射比较接近,但水域上的短波射出辐射比陆地上的大; 长波射入辐射则是陆地比水域的大,而长波射出辐射则是水域的比陆地的大; 两地的净辐射白天接近,夜间水域地区负的净辐射值明显比陆地的大; 9月份,水陆两地的感热通量相差不大,为150～200 W/m2,而潜热通量比感热通量大,天气晴朗时可达到300 W/m2; 11月份,陆地的感热通量比潜热通量大,为100～120 W/m2,而水域地区的感热通量则与潜热通量相当; 两地的潜热通量相差不大,一般不超过50 W/m2.无论是9月还是11月,水域地区夜间都存在水汽向下输送的逆湿现象,而陆地只在9月份存在逆湿现象.2005年9月份的水温观测结果表明,白洋淀水体平均温度比水表平均温度明显偏高,而且日变化幅度很小,水表平均温度则日变化较大.     

LASG Global AGCM with a Two-moment Cloud Microphysics Scheme:Energy Balance and Cloud Radiative Forcing Characteristics

Cloud dominates influence factors of atmospheric radiation, while aerosol–cloud interactions are of vital importance in its spatiotemporal distribution. In this study, a two-moment(mass and number) cloud microphysics scheme, which significantly improved the treatment of the coupled processes of aerosols and clouds, was incorporated into version 1.1 of the IAP/LASG global Finite-volume Atmospheric Model(FAMIL1.1). For illustrative purposes, the characteristics of the energy balance and cloud radiative forcing(CRF) in an AMIP-type simulation with prescribed aerosols were compared with those in observational/reanalysis data. Even within the constraints of the prescribed aerosol mass, the model simulated global mean energy balance at the top of the atmosphere(TOA) and at the Earth's surface, as well as their seasonal variation, are in good agreement with the observational data. The maximum deviation terms lie in the surface downwelling longwave radiation and surface latent heat flux, which are 3.5 W m-2(1%) and 3 W m-2(3.5%), individually. The spatial correlations of the annual TOA net radiation flux and the net CRF between simulation and observation were around 0.97 and 0.90, respectively. A major weakness is that FAMIL1.1 predicts more liquid water content and less ice water content over most oceans. Detailed comparisons are presented for a number of regions, with a focus on the Asian monsoon region(AMR). The results indicate that FAMIL1.1 well reproduces the summer–winter contrast for both the geographical distribution of the longwave CRF and shortwave CRF over the AMR. Finally, the model bias and possible solutions, as well as further works to develop FAMIL1.1 are discussed.     

Radiation Exchange Between Stratus Clouds and Polar Marine Surfaces

The radiative energy exchange between arctic sea-ice and stratiform clouds is studied by means of aircraft measurements and a two-stream radiation transfer model. The data have been obtained by flights of two identically instrumented aircraft during the Radiation and Eddy Flux Experiments REFLEX I in autumn 1991 and REFLEX II in winter 1993 over the arctic marginal ice zone of Fram Strait. The instrumental equipment comprised Eppley pyranometers and pyrgeometers, which measure the solar and terrestrial upwelling and downwelling hemispheric radiation flux densities, and a line-scan-camera on one aircraft to monitor the surface structure of the sea-ice. An empirical parametrization of the albedo of partly ice-covered ocean surfaces is obtained from the data, which describes the albedo increasing linearly with the concentration of the snow-covered sea-ice and with the cosine of the sun zenith angle at sun elevations below 10°. Cloud optical parameters, such as single scattering albedo, asymmetry factor and shortwave and longwave height-dependent extinction coefficient are determined by adjusting modeled radiation flux densities to observations. We found significant influence of the multiple reflection of shortwave radiation between the ice surface and the cloud base on the radiation regime. Consistent with the data, a radiation transfer model shows that stratus clouds of 400 m thickness with common cloud parameters may double the global radiation at the surface of sea-ice compared to open water values. The total cloud-surface-albedo under these circumstances is 30% larger over sea-ice than over water. Parametrizations of the global and reflected radiation above and below stratus clouds are proposed on the basis of the measurements and modeling. The upwelling and downwelling longwave emission of stratus clouds with thicknesses of more than 500 m can be satisfactorily estimated by Stefan's law with an emissivity of nearly 1 and when the maximum air temperature within the cloud is used.     

1998年南海季风试验期间海 气通量的估算

根据1998年南海季风试验西沙海面铁塔梯度观测资料，利用总体（Bulk）系数法和多层结通量廓线法对西沙海面的海-气通量进行了估算，得出两种方法估算的潜热通量、感热通量基本一致。总体系数法估算的潜热通量比多层结通量廓线法略大1～3 W·m-2，感热通量小0～1.5 W·m-2。一般而言，季风爆发期间潜热输送逐渐增加；季风爆发前期夜间潜热通量比季风爆发后期大；季风爆发后期，白天潜热通量明显大于爆发初期和中期。感热通量季风爆发前海面向大气输送，爆发后期大气向海面输送。动量通量和摩擦速度随风速增加。     

FY-4A AGRI辐射率资料偏差特征分析及订正试验

风云四号A星（Fengyun-4A,简称FY-4A）作为我国最新一代静止气象卫星,各方面技术指标都体现了“高、精、尖”特色,处于国际领先地位。其上搭载的多通道扫描成像辐射计（Advanced Geosynchronous Radiation Imager,简称AGRI）较上一代静止卫星风云二号的可见光红外自旋扫描辐射仪观测精度更高、扫描时间更短,充分体现AGRI观测资料将有效提高“一带一路”沿线国家和地区的天气预报和灾害预警水平。偏差订正是卫星资料处理的重要环节之一,因此本文通过在WRFDA v3.9.1（Weather Research and Forecasting model’s Data Assimilation v3.9.1）搭建AGRI同化接口,利用RTTOV v11. 3辐射传输模式和GFS全球预报系统（Global Forecast System）分析场研究了FY-4A AGRI红外通道8～14晴空辐射率资料的偏差特征并进行偏差订正对比试验,分析了卫星天顶角对AGRI资料偏差订正的影响,为将来实现AGRI红外通道辐射率资料在中尺度模式中的同化应用奠定基础。结果表明:（1）通道8～10及14为正偏差,通道11～13为负偏差。水汽通道9和10偏差及其标准差相对较小,偏差海陆差异不明显。通道11～14探测高度较低,陆地上观测受地表发射率影响大,质量控制时可剔除这些通道陆地上的观测。（2）各通道偏差随卫星天顶角变化的拟合直线斜率都小于0.035,对比试验结果表明偏差与卫星天顶角的关系不明显,预报因子中无需考虑卫星天顶角的作用。（3）通道8及11～14的偏差随着目标亮温的变化比水汽通道9～10明显,偏差有较强的目标亮温依赖特征。（4）根据分析的偏差特征对2018年5月13日18时（协调世界时,下同）至15日18时进行变分偏差订正试验,系统性偏差得到了有效的订正。     

Land surface temperature shaped by urban fractions in megacity region

The influence of spatial scales on surface fluxes is an interesting but not fully investigated question. This paper presents an analysis on the influence of spatial scales on surface fluxes in the north Tibetan Plateau based on eddy covariance (EC) and large aperture scintillometer (LAS) data at site Nagqu/BJ, combined with the land surface temperature (LST) and normalized difference vegetation index (NDVI) of moderate-resolution imaging spectroradiometer (MODIS). The analysis shows that sensible heat fluxes calculated with LAS data (H_LAS) agree reasonably well with sensible heat fluxes calculated with EC data (H_EC) in the rain and dry seasons. The difference in their footprints due to the wind direction is an important reason for the differences in H_EC and H_LAS. The H_LAS are statistically more consistent with H_EC when their footprints overlap than when their footprints do not. A detailed analysis on H_EC and H_LAS changes with net radiation and wind direction in rain and dry season indicates that the spatial heterogeneity in net radiation created by clouds contributes greatly to the differences in H_EC and H_LAS in short-term variations. A significant relationship between the difference in footprint-weighted averages of LST and difference in H_EC and H_LAS suggests that the spatial heterogeneity in LST at two spatial scales is a reason for the differences in H_EC and H_LAS and that LST has a positive correlation with the differences in H_EC and H_LAS. A significant relationship between the footprint-weighted averages of NDVI and the ratio of sensible heat fluxes at two spatial scales to net radiation (H/Rn) in the rain season supports the analysis that the spatial heterogeneity in canopy at two spatial scales is another reason for differences in H_EC and H_LAS and that canopy has a negative correlation with (H/Rn). An analysis on the influence of the difference in aerodynamic roughness lengths at two spatial scales on sensible heat fluxes shows that the influence is greater in the dry season and smaller in the rain season because the ratio of z_{0m_LAS} to z_{0m_EC} is big in the dry season and is close to 1.0 in the rain season. This study on spatial scales on surface fluxes in the Tibetan Plateau will be helpful in analyzing and understanding its influence on climate.