Radiative surface temperature and energy balance of a wheat canopy

The sensible heat loss from a stand of winter wheat was calculated from radiometric measurements of crop surface temperature, measurements of air temperature, and an atmospheric resistance to momentum transfer; corresponding latent heat flux was obtained through the energy balance equation. These estimates of sensible and latent heat were compared with fluxes from the Bowen Ratio method. When radiative temperature was derived using a measured canopy emissivity of 0.98, calculations of sensible heat flux were systematically 50–100 W m^-2 less than Bowen Ratio values. The two techniques agreed more closely when an apparent emissivity of 0.96 was used with an apparent reflectivity of 0.03. The mean difference between the estimates of latent heat flux was then -16 ± 32 W m^-2.The surface temperature method showed less systematic error in comparison with the Bowen Ratio values than did estimates using the aerodynamic method.On leave from: University of Nottingham, School of Agriculture, Loughborough LE12 5RD.     

青藏高原中部季节冻土区地表能量通量的模拟分析

利用“全球协调加强观测计划之亚澳季风青藏高原试验(CAMP/Tibet)”中那曲地区BJ站2002年8月1日\_2003年8月31日的观测资料作为水热耦合模式(Simultaneous Heat and Water, SHAW)的强迫场,对青藏高原中部季节冻土区地表能量通量特征进行了单点模拟研究。通过对实测值与模拟结果的对比分析,发现SHAW模式能较成功地模拟该地区地表能量通量特征, 短波净辐射和长波净辐射的模拟值与观测值吻合较好, 净辐射和土壤热通量在夏半年的模拟值与观测值也吻合,但相对夏\, 秋季而言,它们在冬\, 春季的模拟值较观测值略偏大。模拟的感热和潜热通量的季节变化比较合理,由模拟的感热和潜热通量计算的Bowen比能较好地解释不同季节太阳辐射的能量转化。     

The Summer Surface Energy Balance of the High Antarctic Plateau

The summertime surface energy balance (SEB) at Kohnen station, situated on the high Antarctic plateau (75°00′ S, 0°04′ E, 2892m above sea level) is presented for the period of 8 January to 9 February 2002. Shortwave and longwave radiation fluxes were measured directly; the former was corrected for problems associated with the cosine response of the instrument. Sensible and latent heat fluxes were calculated using the bulk method, and eddy-correlation measurements and the modified Bowen ratio method were used to verify these calculated fluxes. The calculated sub-surface heat flux was checked by comparing calculated to measured snow temperatures. Uncertainties in the measurements and energy-balance calculations are discussed. The general meteorological conditions were not extraordinary during the period of the experiment, with a mean 2-m air temperature of −27.5°C, specific humidity of 0.52×10⁻³kg kg⁻¹ and wind speed of 4.1ms⁻¹. The experiment covered the transition period from Antarctic summer (positive net radiation) to winter (negative net radiation), and as a result the period mean net radiation, sensible heat, latent heat and sub-surface heat fluxes were small with values of −1.1, 0.0, −1.0 and 0.7 Wm⁻², respectively. Daily mean net radiation peaked on cloudy days (16 Wm⁻²) and was negative on clear-sky days (minimum of −19 W m⁻²). Daily mean sensible heat flux ranged from −8 to +10 Wm⁻², latent heat flux from −4 to 0 Wm⁻² and sub-surface heat flux from −8 to +7 Wm⁻².     

柽柳灌丛热量收支特性与蒸散研究

Bowen能量平衡法是广泛用于测定各种低矮植物蒸散的常用方法。本文将改进的波文比—能量观测系统用于测定灌木柽柳群落的测定，通过6～9月对感热通量、潜热通量、土壤热通量等的测定，计算出额济纳地区柽柳灌丛(6～9月)的蒸散量为335．31mm；在8月潜热通量占能量支出量的62．85％，感热通量占32．85％，土壤热通量占4．44％。在日变化中，潜热在上午大于感热，下午感热交换大于潜热。     

青藏高原不同地区湍流输送特征及其与气象因子的关系

利用第三次青藏高原大气科学观测试验数据,对高原不同地区感热、潜热交换等湍流输送特征进行了分析,并进一步对比研究了其与气象环境因子的相关关系。结果表明:（1）高原各站之间感热和潜热的差异性较大,但大多在雨季潜热会大于感热。干燥的狮泉河站属于高寒荒漠地区,降水极少,全年感热都远大于潜热,波文比年平均值可达到20.0;湿润的比如站和嘉黎站潜热在4～10月均显著大于感热,波文比在4～10月的数值范围在0.27～0.88。（2）高原感热和潜热通量的季节变化与高原季风所处的地理位置有密切关系,高原中部的感热通量在3～5月达到最大值,而高原西部则在4～6月最大,可能与高原季风的活动有关。（3）通过与气象要素的相关分析表明,高原西部狮泉河站感热与地气温差的正相关关系最为显著,全年的相关系数可以达到0.905,在4个季节相关系数也均大于0.79,这可能与下垫面是裸地有关;高原中部安多站和那曲站感热与风速的正相关在夏季最为显著,比如站感热与风速的正相关在冬季最为明显,而狮泉河站感热与风速在春、夏季均有着十分显著的正相关。     

Key results and implications from phase 1(c) of the Project for Intercomparison of Land-surface Parametrization Schemes

 Using atmospheric forcing data generated from a general circulation climate model, sixteen land surface schemes participating in the Project for the Intercomparison of Land-surface Parametrization Schemes (PILPS) were run off-line to equilibrium using forcing data from a GCM representative of a tropical forest and a mid-latitude grassland grid point. The values for each land surface parameter (roughness length, minimum stomatal resistance, soil depth etc.) were provided. Results were quality controlled and analyzed, focusing on the scatter simulated amongst the models. There were large differences in how the models’ partitioned available energy between sensible and latent heat. Annually averaged, simulations for the tropical forest ranged by 79 1 3;W m^-2 for the sensible heat flux and 80 W m^-2 for the latent heat flux. For the grassland, simulations ranged by 34 W m^-2 for the sensible heat flux and 27 W m^-2 for the latent heat flux. Similarly large differences were found for simulated runoff and soil moisture and at the monthly time scale. The models’ simulation of annually averaged effective radiative temperature varied with a range, between all the models, of 1.4 K for tropical forest and 2.2 K for the grassland. The simulation of latent and sensible heat fluxes by a standard ‘bucket’ models was anomalous although this could be corrected by an additional resistance term. These results imply that the current land surface models do not agree on the land surface climate when the atmospheric forcing and surface parameters are prescribed. The nature of the experimental design, it being offline and with artificial forcing, generally precludes judgements concerning the relative quality of any specific model. Although these results were produced de-coupled from a host model, they do cast doubt on the reliability of land surface schemes. It is therefore a priority to resolve the disparity in the simulations, understand the reasons behind the scatter and to determine whether this lack of agreement in de-coupled tests is reproduced in coupled experiments. Received: 15 October 1997 / Accepted: 22 April 1999     

白洋淀水陆不均匀地区能量平衡特征分析

应用2005年9月在河北白洋淀地区进行的大气边界层综合观测实验资料, 对水陆不均匀地表条件下的白洋淀地区陆地的能量平衡特征进行了分析。结果表明: (1) 该地区存在能量不闭合现象。涡动相关法得到的感热、 潜热之和仅为有效能的75%, 其中涡动相关法得到的潜热通量为Bowen比法得到的潜热通量的70%, 而涡动相关法得到的感热通量为Bowen比法得到的感热通量的77% 。 (2) 地表潜热通量和感热通量随着净辐射的变化而变化。但潜热通量明显比感热通量大, 净辐射主要消耗于地表的水汽蒸发。 (3) 该地区白天的Bowen比平均在-0.4~0.4之间, 总体平均为0.131。受天气条件影响较大, 有明显的日变化, 午后15:00以后近地面层会出现逆温, Bowen比变为负值。 (4) 能量闭合程度有一定的日变化, 随着太阳高度角的增大而增大。     

Surface fluxes estimation over agricultural areas. Comparisonof methods and the effects of land surface inhomogeneity

Summary  The Bowen Ratio-Energy Balance (BREB) and the aerodynamic method were used to estimate turbulent fluxes of sensible and latent heat flux over an irrigated agricultural area (IAA) and over two dry agricultural areas (DAA1 and DAA2). These turbulent fluxes were analysed and particular attention paid to two specific areas. First, a quantitative analysis of sensible and latent heat fluxes obtained by the BREB method was carried out, taking into account different soil type, vegetation and surface conditions. The results showed that in IAA latent heat flux was higher than sensible heat flux, except in summer months, while in DAA1 and DAA2, sensible heat flux was higher except in the months when the vegetation was at the stage of maximum development. Second, sensible and latent heat fluxes estimates from the BREB method were compared with those obtained from the aerodynamic method. In this comparison factors such as soil type, soil vegetation cover, homogeneity or inhomogeneity of terrain and mesoscale effects such as orography and wind patterns were taken into account. The results show that in conditions of light wind, the two methods only concur if the condition of horizontal homogeniety is fulfilled. The influence of inhomogeneity seems to decrease and agreement between methods improves, if the wind is stronger and the effects of meso and synoptic scales are predominant. Received May 18, 1999/Revised March 15, 2000     

THE ENERGY BUDGETS UNDER DIFFERENT SYNOPTIC CONDITIONS OVER HUAIHE RIVER BASIN DURING HUBEX FIELD OBSERVATION PERIODS IN 1999*

In different synoptic conditions and at different time scales,the analysis of the energy budgets by Bowen Ratio Method and Bulk Schemes over Huaihe River Basin during the field observation periods of HUBEX in 1999 shows that,(1) the averaged latent heat flux is an order of magnitude more than the averaged sensible heat flux during the observation period:(2) the variation of totalcloud amount is out of phase with the terms of energy budgets except for the downward longwave radiation which maybe is related to the cloud's height and class:(3) the values of sensible and latent heat fluxes are small during rain episodes,but thereafter,the values become high and then up to maximum.It is similar to the other terms of the energy budgets except for the downward longwave radiation.The diurnal variation of energy budgets indicates that the daytime precipitation exerts great influence to the energy budgets,but the nighttime precipitation makes little influence;(4) the variation of the latent heat flux is in phase with the evaporation,which indicates that the latent heat flux calculated by bulk schemes is reliable:(5) the means of the sensible and latent heat flux and momentum flux by bulk schemes for the time period from May to August are,respectively,30.71W/m².116.81W/m².2.86×10^-2N/m² in 1998 and 30.28W/m²,107.35W/m²,2.74×10^-2N/m² in 1999.The values of these two years are similar.During summer in 1999 the magnitude and activity of sensible heat flux are strongest in June and those of the latent heat flux are in August.     

青藏高原湿地土壤冻结、融化期间的陆面过程特征

利用青藏高原中部玉树隆宝湿地2015年7月-2016年7月的观测资料,分析了土壤冻结、融化前后土壤温、湿度和地表能量收支特征,结果表明：冻土持续时期为12月至次年4月,深层土壤的冻结较浅层土壤滞后,融化过程快于冻结过程,5-40 cm土壤全部冻结历时51 d,全部融化历时19 d。土壤体积含水量年变化幅度达0.6 m³/m³。冻结过程5-40 cm土壤体积含水量下降,融化过程5-10 cm土壤体积含水量升高。土壤冻结之后,感热通量白天的值升高,潜热通量白天的值降低,净辐射和土壤热通量均降低,土壤热通量日变化幅度增大。土壤融化之后,潜热通量、净辐射和土壤热通量白天的值升高。地表反照率、鲍恩比、土壤热导率和土壤热扩散率冻结后增大融化后减小,土壤热容量冻结后减小融化后增大。     

Energy partitioning at treeline forest and tundra sites and its sensitivity to climate change

Abstract

Summertime energy budgets of contiguous wetland tundra and forest near Churchill, Manitoba along the coast of Hudson Bay were measured over a five year period, 1989–1993. An examination of differences in energy budgets between the two sites showed that net radiation was similar in all years. Soil heat flux was greater at the tundra site in most, but not all, years. However, sensible heat flux was always larger at the forest site and latent heat flux was always greater at the tundra site. Mean daily Bowen ratios at both sites were less than unity in all years. Average Bowen ratios for the five years were 0.45 for tundra and 0.66 for forest. Wind direction is used as an analogue for changing climatic conditions where onshore winds are cooler and moister than offshore winds. Sensible and latent heat fluxes at both sites varied significantly between onshore and offshore wind regimes. However, differences between onshore and offshore fluxes at the tundra site were larger than for the forest. Thus, Bowen ratios also varied more at the tundra site. We have plotted the ratio of tundra‐to‐forest Bowen ratios as a measure of the relative sensitivity of energy partitioning to climatic change. The ratio decreases with increasing vapour pressure deficit (and increasing air temperature). We interpret these results as suggesting that energy partitioning over the wetland tundra is more sensitive to changes in climate than the treeline forest environment. Thus, as the climate warms and becomes drier, more additional energy goes into evaporation of water from the wetland tundra than from the forest.     

广州番禺地区草地陆气相互作用观测研究

介绍了2004年在广州番禺进行的陆气相互作用观测试验。观测研究表明:新型的超声风温仪虽然带有雨滴防护沙网, 但雨滴对超声观测的误差影响显著, 尤其是对u, w方向。雨天情况下与z/L相关系数很低, 湍流强度与稳定度不存在1/3次方关系。涡动相关法和能量平衡法计算的感热通量及潜热通量比较接近, 感热、潜热通量相关系数分别达到0.8699和0.8633, 两种方法带来的误差主要发生在近地层稳定度发生明显变化的时刻, 即在午间热通量的峰值或傍晚或晚间热通量的低值, 其中能量平衡法计算的感热、潜热普遍具有较大的正负峰值。涡动相关法计算的Q_h+Q_e普遍偏小, 与可用能量R_n-Q_g多数情况下存在能量不平衡, 说明了忽略热存储项的地表能量平衡方程的局限性。番禺夏、秋季近地层各能量具有与太阳辐射相似的日变化特征, 但夏季的潜热大于感热, 而秋季则相反。近地面二氧化碳从5—8月是一个减低过程, 尔后上升到12月份浓度最高, 总体浓度值在350×10-6~400×10-6之间变化。     

Validation of the “Lokal-Modell” over heterogeneous land surfaces using aircraft-based measurements of the REEEFA experiment and comparison with micro-scale simulations

Summary An aircraft-based experimental investigation of the atmospheric boundary layer (ABL) structure and of the energy exchange processes over heterogeneous land surfaces is presented. The measurements are used for the validation of the mesoscale atmospheric model “Lokal-Modell” (LM) of the German Weather Service with 2.8 km resolution. In addition, high-resolution simulations using the non-hydrostatic model FOOT3DK with 250 m resolution are performed in order to resolve detailed surface heterogeneities. Two special observation periods in May 1999 show comparable convective boundary layer (CBL) conditions. For one case study vertical profiles and area averages of meteorological quantities and energy fluxes are investigated in detail. The measured net radiation is highly dependent on surface albedo, and the latent heat flux exhibits a strong temporal variability in the investigation area. A reduction of this variability is possible by aggregation of multiple flight patterns. To calculate surface fluxes from aircraft measurements at low altitude, turbulent energy fluxes were extrapolated to the ground by the budget method, which turned out to be well applicable for the sensible heat flux, but not for the latent flux. The development of the ABL is well captured by the LM simulation. The comparison of spatiotemporal averages shows an underestimation of the observed net radiation, which is mainly caused by thin low-level clouds in the LM compared to observed scattered CBL clouds. The sensible heat flux is reproduced very well, while the latent flux is highly overestimated especially above forests. The realistic representation of surface heterogeneities in the investigation area in the FOOT3DK simulations leads to improvements for the energy fluxes, but an overestimation of the latent heat flux still persists. A study of upscaling effects yields more structures than the LM fields when averaged to the same scale, which are partly caused by the non-linear effects of parameter aggregation on the LM scale.     

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     

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。     

6种地表热通量资料在伊朗—青藏高原地区的对比分析

基于JRA25、ERA40、ERA-Interim、NCEP1、NCEP2和20CR,对比了不同资料中气候平均(1979—2008年)伊朗—青藏高原感热通量和波文比的季节演变,以及夏季高原感热的年际变率和线性趋势。6套资料均表明,由春到夏亚洲大地形区域地表热状况的季节演变存在明显差异,青藏高原东南部低空气旋生成,一方面增多了局地降水,减弱了地表西风,造成潜热加强,感热减弱,波文比减小;另一方面加强了伊朗高原的东北风,抑制了当地降水,令感热加强,波文比增加,构成了青藏—伊朗高原感热通量季节演变的纬向非对称分布。虽然近30 a来伊朗高原(青藏高原)夏季感热线性增加(减小)的趋势一致,但不同资料所反映的伊朗—青藏高原夏季感热通量的年际变化差别明显。     

SURFACE IMBALANCE ENERGY CALCULATED AND ANALYZED WITH THE DATA OF EBEX-2000*

Mainly.three methods have been developed to calculate turbulence heat flux.They are eddy covariance method,Bowen ratio/energy balance method and aerodynamic method.In this paper, all the three methods have been used to calculate sensible heat flux,latent heat flux and imbalance energy near the surface with the experiment data of EBEX-2000.Then comparisons of the three methods and some possible explanations of the surface imbalance energy are given.     

Airborne measurements of turbulent fluxes during LITFASS-98: Comparison with ground measurements and remote sensing in a case study

Summary ?Simultaneous flight measurements with the research aircraft Do 128 and the helicopter-borne turbulence probe Helipod were performed on 18 June 1998 during the LITFASS-98 field experiment. The area-averaged turbulent vertical fluxes of momentum, sensible, and latent heat were determined on a 15 km × 15 km and a 10 km × 10 km flight pattern, respectively. The flights were carried out over heterogeneous terrain at different altitudes within a moderately convective boundary layer with Cumulus clouds. Co-spectra-analysis demonstrated that the small scale turbulent transport was completely sampled, while the comparatively small flight patterns were possibly of critical size regarding the large-scale turbulence. The phygoide of the airplane was identified as a significant peak in some co-spectra. The turbulent fluxes of momentum and sensible heat at 80 m above the ground showed systematic dependence on the location of the flight legs above the heterogeneous terrain. This was not observed for the latent heat flux, probably due to the vertical distribution of humidity in the boundary layer. Statistical error analysis of the fluxes F showed that the systematic statistical error ΔF was one order of magnitude smaller than the standard deviation σ _F . The difference between area-averaged fluxes derived from simultaneous Helipod and Do 128 measurements was much smaller than σ _F , indicating that the systematic statistical error was possibly over-estimated by the usual method. In the upper half of the boundary layer the airborne-measured sensible heat flux agreed well with windprofiler/RASS data. A linear fit was the best approximation for the height dependence of all three fluxes. The linear extrapolations of the latent and sensible heat fluxes to the ground were in good agreement with tower, scintillometer, and averaged ground-station measurements on various surface types. Systematic discrepancies between airborne and ground-based measurements were not found. Received June 18, 2001; revised December 21, 2001; accepted June 3, 2002     

ESTIMATES OF SEA SURFACE FLUXES DURING TOGA-COARE IOP

With the marine ship observation data set obtained by three cruise-phases of Chinese Xi-angyanghong 5 from November 5,1992 to February 19,1993 in the TOGA-COARE IOP at 2°S,156°E.the sea surface fluxes at this point are estimated by three different bulk schemes.Firstly.aquasi-linear relation is found between the neutral drag coefficients and wind speed.Then,the sta-bility-dependent drag and heat transfer coefficients are solved in the iterative method.Based onthus-derived transfer coefficients,the momentum,sensible and latent heat fluxes are calculated.In the warm pool region,the fluxes corresponding to the westeily winds are much greater thanthose of the easterly trade winds.The magnitude of sea surface fluxes depends upon the atmo-spheric stability as well,in particular in the case of weak wind condition.The estimated sea sur-face net heat budget shows that considerable amount of heat transport from ocean to atmosphere ismainly produced by the effective longwave radiation,latent and sensible heat fluxes.Among themthe value of latent heat flux is the largest and the sensible heat flux is the smallest.Finally,an ac-curacy analysis is made by direct measurements with the eddy-correlation method on the JapaneseR/V Hakuho board at the same time.It is shown that the bulk-derived fluxes are acceptable withmuch confidence.The estimated effective longwave radiation is used to compare with those by di-rect observations on Xiangyanghong 5.This research is compared with TOGA investigation in thetropical western Pacific.     

Modelling sensible and latent heat fluxes over sea during unstable,very close to neutral conditions

During slightly unstable but still very close to neutral conditions new results from two previous investigations have shown a significant increase of sensible and latent heat fluxes over the sea. The vertical heat transport during these conditions is dominated by detached eddies originating at the top of the boundary layer, bringing relatively cold and dry air to the surface. This effect can be described in numerical models by either enhanced heat transfer coefficients for sensible and latent heat (Stanton and Dalton numbers respectively) or with an additional roughness length, added to the original roughness lengths for heat and humidity. Such new expressions are developed using turbulence measurements from the Baltic Sea valid for wind speeds up to 14 m s⁻¹. The effect of including the increased heat fluxes is investigated using two different numerical models: a regional three-dimensional climate model covering northern Europe, and a process-oriented ocean model for the Baltic Sea. During periods of several days, the latent heat flux can be increased by as much as 100 W m⁻². The increase in sensible heat flux is significantly smaller since the process is only of importance in the very near-neutral regime where the sensible heat flux is very small. The long-term average effect over the Baltic Sea is of the order of several W m⁻².