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1.
Stephanie K. Kampf Scott W. Tyler Cristin A. Ortiz Jos F. Muoz Paula L. Adkins 《Journal of Hydrology》2005,310(1-4):236-252
Playa systems are driven by evaporation processes, yet the mechanisms by which evaporation occurs through playa salt crusts are still poorly understood. In this study we examine playa evaporation as it relates to land surface energy fluxes, salt crust characteristics, groundwater and climate at the Salar de Atacama, a 3000 km2 playa in northern Chile containing a uniquely broad range of salt crust types. Land surface energy budget measurements were taken at eight representative sites on this playa during winter (August 2001) and summer (January 2002) seasons. Measured values of net all-wave radiation were highest at vegetated and rough halite crust sites and lowest over smooth, highly reflective salt crusts. Over most of the Salar de Atacama, net radiation was dissipated by means of soil and sensible heat fluxes. Dry salt crusts tended to heat and cool very quickly, whereas soil heating and cooling occurred more gradually at wetter vegetated sites. Sensible heating was strongly linked to wind patterns, with highest sensible heat fluxes occurring on summer days with strong afternoon winds. Very little energy available at the land surface was used to evaporate water. Eddy covariance measurements could only constrain evaporation rates to within 0.1 mm d−1, and some measured evaporation rates were less than this margin of uncertainty. Evaporation rates ranged from 0.1 to 1.1 mm d−1 in smooth salt crusts around the margin of the salar and from 0.4 to 2.8 mm d−1 in vegetated areas. No evaporation was detected from the rugged halite salt crust that covers the interior of the salar, though the depth to groundwater is less than 1 m in this area. These crusts therefore represent a previously unrecorded end member condition in which the salt crusts form a practically impermeable barrier to evaporation. 相似文献
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Charles I. Essery 《Journal of Hydrology》1992,130(1-4):171-187
Water balances have been constructed for three catchments using monthly data on rainfall (P), evapotranspiration (ET), stream discharge (Q) and groundwater levels. Length of record on the three catchments is 12, 8 and 6 years. Monthly, seasonal, and annual residuals (R) of the surface water balance equation R = P − Q − ET are used to infer changes in groundwater storage and are plotted against observed changes in groundwater storage (WTD). Linear regression analysis between R and WTD is used to examine the nature of the catchments' storage characteristics, the watertightness of the catchments, and the possibility that systematic measurement errors accumulate as the balance period lengthens. 相似文献
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目前遥感干旱监测方法的精度普遍不高,探求新的遥感干旱监测方法有助于干旱监测预警技术的提升与发展.波文比是感热通量与潜热通量之比,能综合反映地表水热特征,可尝试将其引入到遥感干旱监测领域加以利用.应用甘肃河东地区的EOS-MODIS卫星资料和同步地面气象资料,基于地表能量平衡原理构建了波文比干旱监测模型,对比分析了波文比(β)指数、温度植被指数(TVX)与土壤水分的相关性,并以典型晴空影像(2014年10月5日)为例初步建立了β的干旱分级标准,对研究区进行了旱情评估.结果表明:β与土壤相对湿度呈现出高度负相关,相比于当下广泛应用的TVX,β与0~20cm平均土壤相对湿度具有更好的相关性,监测精度得到了显著提高.用β干旱分级标准评估的研究区干湿状况与前期降水空间分布吻合得相当好,评估表明2014年10月5日研究区基本为适宜(无旱),与2014年9月的降水距平百分率特征一致.基于地表能量平衡的波文比(β)指数在干旱监测中效果突出,具有很好的应用前景. 相似文献
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湖泊模型为数值天气预报模型提供热量通量、水汽通量和动量通量等下边界条件,但是不同时间尺度上湖泊水热通量变化的控制因子不同,因此有必要对湖泊模型进行多时间尺度上的离线评估.本文利用2012-2016年太湖中尺度通量网避风港站的气象资料和辐射数据驱动CLM4-LISSS模型(Community Land Model version 4-Lake,Ice,Snow and Sediment Simulator),并与涡度相关观测(Eddy Covariance,EC)结果进行对比,以年平均潜热通量模拟结果最佳为目标调整了模式中的消光系数、粗糙度长度方案,研究了该模型从半小时到年尺度上对湖表温度和水热通量的模拟性能.结果表明:模型对湖表温度的模拟在各时间尺度上均比较理想,但是模拟的日较差较小;从半小时到年尺度上潜热通量的变化趋势都能被很好地模拟出来,但在季节尺度上,潜热通量的模拟出现了秋冬季偏高、春夏季偏低的情况,季节变化模拟不准确.湖表温度和潜热通量模拟偏差的原因可能是消光系数的参数化方案.相比之下,感热通量尽管年际变化趋势的模拟值与观测值一致,但是从半小时到年尺度均被高估.特别地,冷锋过境期间,模型能较好地模拟出潜热通量和感热通量的变化趋势,但对于高风速条件下的感热通量模拟效果不佳.本文的研究结果能为湖泊模式的应用与发展提供有用信息. 相似文献
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为了研究城市化进程对城市边界层结构的影响,通过高分辨率的卫星遥感资料获得土地利用类型,以及地表反照率、植被指数等地表参数,以南京为例,运用数值模拟手段进行了研究,结果显示这是一种可行的手段.数值模拟结果表明,随着城市的发展,城市反照率减小、植被减少、地表湿度减小,蒸发耗热减少,感热通量增加140 W/m2,城市波恩比增加.地表和大气之间热量交换加强,湍流热量通量增大了一倍,湍流交换发展加剧,14：00混合层高度抬高了500 m.地表湍流水汽通量和空气中水汽含量都减小,这也使更多的热量用于加热地表和大气,使地温、气温的日变化幅度增加. 相似文献
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Observational estimation of heat budgets on drifting ice and open water over the Arctic Ocean 总被引：9，自引：0，他引：9
It is of major scientific interests to determine the parameters of momentum, heat and vapor exchange in the planetary boundary layer in order to study the effects of ocean-ice-atmosphere interactions and their feedback mechanisms on global climate[1]. Lin… 相似文献
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Jiabing Wu Dexin Guan Shijie Han Tingting Shi Changjie Jin Tiefan Pei Guirui Yu 《水文研究》2007,21(18):2425-2434
Components of the energy budget were measured continuously above a 300‐year‐old temperate mixed forest at the Changbaishan site, northeastern China, from 1 January to 31 December 2003, as a part of the ChinaFlux programme. The albedo values above the canopy were lower than most temperate forests, and the values for snow‐covered canopy were over 50% higher than for the snow‐free canopy. In winter, net radiation Rn was generally less than 5% of the summer value due to high albedo and low incoming solar radiation. The annual mean latent heat LE was 37·5 W m?2, accounting for 52% of Rn. The maximum daily evaporation was about 4·6 mm day?1 in summer. Over the year, the accumulated precipitation was 578 mm; this compares with 493 mm of evapotranspiration, which shows that more than 85% of water was returned to the atmosphere through evapotranspiration. The LE was strongly affected by the transpiration activity and increased quickly as the broadleaved trees began to foliate. The sensible heat H dropped at that time, although Rn increased. Consequently, the seasonal variation in the Bowen ratio β was clearly U‐shaped, and the minimum value (0·1) occurred on a sunny day just after rain, when most of the available energy was used for evapotranspiration. Negative β values occurred occasionally in the non‐growing season as a result of intensive radiative cooling and the presence of water on the surface. The β was very high (up to 13·0) in snow‐covered winter, when evapotranspiration was small due to low surface temperature and available soil water. Vegetation phenology and soil moisture were the key variables controlling the available energy partitioning between H and LE. Energy budget closure averaged better than 86% on a half‐hourly basis, with slightly greater closure on a daily basis. The degree of closure showed a dependence on friction velocity u*. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
9.
D. V. Viswanadham A. N. V. Satyanarayana M. K. Srivastava 《Pure and Applied Geophysics》1997,150(1):129-142
—The atmospheric surface layer over land may behave differently in the tropics, particu larly during the monsoon. A preliminary attempt is made to observe the behavior of surface layer characteristics such as fluxes of momentum, sensible heat and latent heat, friction velocity, friction temperature, M-O length scale, Richardson number and Bowen’s ratio over Kharagpur (22°20′N, 87°18′E), a typical moist tropical station. The diurnal and day-to-day variations have been studied. It is observed that during the active phase of the monsoon the sensible heat flux and Bowen’s ratio are low. The diurnal variation is apparent for most parameters. Mostly near neutral conditions are observed. 相似文献
10.
Spatial distribution of surface energy fluxes over the Loess Plateau in China and its relationship with climate and the environment 总被引：1，自引：0，他引：1
Qiang Zhang Liang Zhang Jing Huang LiYang Zhang WenYu Wang Sha Sha 《中国科学:地球科学(英文版)》2014,57(9):2135-2147
China's Loess Plateau is located at the edge of the Asian summer monsoon in a transition zone of climate and ecology. In the Loess Plateau, climate and environments change along with space, which has an obvious impact on the spatial distribution of surface energy fluxes. Because of scarce land-surface observation sites and short observation time in this area, previous studies have failed to fully understand the land-surface energy balance characteristics over the entire the Loess Plateau and their effect mechanisms. In this paper, we first test the simulation ability of the Community Land Model(CLM) model by comparing its simulated data with observed data. Based on the simulation data for the Loess Plateau over the past thirty years, we then analyze the spatial distribution of surface energy fluxes and compare the pattern differences between the area averages for the driest year and wettest year. Furthermore, we analyze the relationship between the spatial distribution of the components of the surface energy balance with longitude, latitude, altitude, precipitation and temperature. The main results are as follows: the spatial distribution of surface energy fluxes are significantly different, with the surface net radiation and sensible heat flux increasing from south to north and latent heat flux and soil heat flux decreasing from southeast to northwest. The sensible heat flux at the driest point is nearly twice as high as that at the wettest point, whereas the latent heat flux and soil heat flux at the driest point are half as much as that at the wettest point. The impact of variations of annual precipitation on the components of the surface energy balance is also obvious, and the maximum magnitude of the changes to the sensible heat flux and latent heat flux is nearly 30%. To a certain extent, geographical factors(including longitude, latitude, and altitude) and climate factors(including temperature and precipitation) affect the surface energy fluxes. However, the surface net radiation is more closely related to latitude and altitude, sensible heat flux is more closely related to the monsoon rainfall and latitude, and latent heat flux and soil heat flux are more closely related to the monsoon rainfall. 相似文献
11.
This paper presents measurements of the energy balance (radiation, sensible heat flux, evaporation) from a sub‐arctic hillside in northern Finland for a summer season. Comparisons are also made with a nearby wetland site. The hillslope measurements show an equal partition of the radiant energy into sensible and latent heat flux. The evaporative ratio of just over one half was remarkably constant throughout the season, despite very large day‐to‐day and diurnal variations of temperature, humidity deficit and radiation input. This conservative behaviour of the evaporation was caused by a strong rise in effective surface resistance to evaporation with increasing vapour pressure deficit. This suggests a strong physiological control on the evaporation, with stomata closing at times of high evaporative demand. There was no obvious impact of soil‐water stress on the evaporation. However, a comparison with the evaporation measured at a nearby mire site in 1997 suggests that the mire has a significantly lower surface resistance, even when the impact of a significantly lower humidity deficit in the earlier year is taken into account. The measurements are used to test, off‐line, the performance of MOSES (Meteorological Office Surface Exchange Scheme), a simple, but comprehensive, land surface model. The sensitivity of the energy exchanges to the thermal properties of the top soil layer (a surrogate for the upper soil/vegetation layer) is investigated with the use of the model. It is found that the evaporation is insensitive to these properties; they do, however, influence the partition of energy between the sensible heat flux and the ground heat flux (and hence the soil temperatures). It is suggested that the model needs to represent the thermal properties of the canopy more realistically. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Information about seasonal crop water consumption is useful to develop the appropriate irrigation scheme. Measurements of energy balance components using the Bowen ratio method were made for a complete growing season at a vineyard in the arid region of northwest China. Vine in the experiment was furrow‐irrigated using a trellis system. The measured evapotranspiration was compared with estimates using the soil water balance method. It is shown that the Bowen ratio method provided accurate estimates of evapotranspiration from the vineyard and this requires that the Bowen ratio system is appropriately installed. The energy balance components showed typical diurnal pattern with peaks that occurred around the midday, except for the ground heat flux which delayed its peak by 2–3 h. The sensible heat flux was greater than the latent heat flux and followed the net radiation closely. The ratio of the latent heat flux to net radiation was low in the early growing season and increased over time. Under the limited irrigation experienced in the vineyard, the latent heat flux was controlled by available soil moisture and the total evapotranspiration in the growing season was 253 mm. The seasonal progression of the crop coefficient is similar to that reported in the literature, with the maximum occurring during the month of September. The crop coefficient can be estimated as a non‐linear function of day of year (DOY) and used to estimate evapotranspiration from vineyards in the region. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Tetsuji Suzuki Takeshi Ohta Tetsuya Hiyama Yasuhiro Izumi Osmund Mwandemele Morio Iijima 《水文研究》2014,28(17):4780-4794
Land use changes in wetland areas can alter evapotranspiration, a major component of the water balance, which eventually affects the water cycle and ecosystem. This study assessed the effect of introduced rice‐cropping on evapotranspiration in seasonal wetlands of northern Namibia. By using the Bowen ratio–energy balance method, measurements of evapotranspiration were performed over a period of 2.5 years at two wetland sites—a rice field (RF) and a natural vegetation field (NVF)—and at one upland field (UF) devoid of surface water. The mean evapotranspiration rates of RF (1.9 mm daytime?1) and NVF (1.8 mm daytime?1) were greater than that in UF (1.0 mm daytime?1). RF and NVF showed a slight difference in seasonal variations in evapotranspiration rates. During the dry season, RF evapotranspiration was less than the NVF evapotranspiration. The net radiation in RF was less in this period because of the higher albedo of the non‐vegetated surface after rice harvesting. In the early growth period of rice during the wet season, evapotranspiration in RF was higher than that in NVF, which was attributed to a difference in the evaporation efficiency and the transfer coefficient for latent heat that were both affected by leaf area index (LAI). Evapotranspiration sharply negatively responded to an increase in LAI when surface water is present according to sensitivity analysis, probably because a higher LAI over a surface suppresses evaporation. The control of LAI is therefore a key for reducing evaporation and conserving water. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Land surface energy fluxes are required in many environmental studies, including hydrology, agronomy and meteorology. Surface energy balance models simulate microscale energy exchange processes between the ground surface and the atmospheric layer near ground level. Spatial variability of energy fluxes limits point measurements to be used for larger areas. Remote sensing provides the basis for spatial mapping of energy fluxes. Remote‐sensing‐based surface energy flux‐mapping was conducted using seven Landsat images from 1997 to 2002 at four contiguous crop fields located in Polk County, northwestern Minnesota. Spatially distributed surface energy fluxes were estimated and mapped at 30 m pixel level from Landsat Thematic Mapper and Enhanced Thematic Mapper images and weather information. Net radiation was determined using the surface energy balance algorithm for land (SEBAL) procedure. Applying the two‐source energy balance (TSEB) model, the surface temperature and the latent and sensible heat fluxes were partitioned into vegetation and soil components and estimated at the pixel level. Yield data for wheat and soybean from 1997 to 2002 were mapped and compared with latent heat (evapotranspiration) for four of the fields at pixel level. The spatial distribution and the relation of latent heat flux and Bowen ratio (ratio of sensible heat to latent heat) to crop yield were studied. The root‐mean‐square error and the mean absolute percentage of error between the observed and predicted energy fluxes were between 7 and 22 W m−2 and 12 and 24% respectively. Results show that latent heat flux and Bowen ratio were correlated (positive and negative) to the yield data. Wheat and soybean yields were predicted using latent heat flux with mean R2 = 0·67 and 0·70 respectively, average residual means of −4·2 bushels/acre and 0·11 bushels/acre respectively, and average residual standard deviations of 16·2 bushels/acre and 16·6 bushels/acre respectively (1 bushel/acre ≈ 0·087 m3 ha−1). The flux estimation procedure from the SEBAL‐TSEB model was useful and applicable to agricultural fields. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Lack of accurate data has led some hydrologists and city planners to assume that urban infiltration is zero and runoff is 100% of the rainfall. These assumptions lead to an over estimation of road runoff volume and an underestimation of direct recharge to groundwater, which is already rising under some UK cities. This study investigates infiltration and runoff processes and quantifies the percentage of rainfall that contributes to storm drainage, and that which infiltrates through different types of road surface. Access tubes were installed for measuring soil water content using a neutron probe in three car parks, a road and a grass site at the Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford. Storm drainage was recorded at the exit of the Thamesmead Estate in Crowmarsh Gifford, just before the drain joins the River Thames at Wallingford. Rainfall and water table depth were also recorded. Weekly measurements of soil moisture content indicated that the top 40 cm layer is not influenced by water‐table fluctuations and, therefore, positive changes in soil moisture could be attributed to infiltration of rainfall through the surface. Depending on the nature of the surface, subsurface layers, level of traffic, etc., between 6 and 9% of rainfall was found to infiltrate through the road surfaces studied. The storm drainage generated by road runoff revealed a flow pattern similar to that of the receiving watercourse (River Thames) and increased with the increase of infiltration and soil water content below the road surface. The ratio of runoff to rainfall was 0·7, 0·9 and 0·5 for annual, winter (October–March) and summer (April–September) respectively. As the results of the infiltration indicated that 6 to 9% of annual rainfall infiltrates through the road surface, this means that evaporation represents, 21–24% of annual rainfall, with more evaporation taking place during summer than winter. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
17.
Discussion and reassessment of the method used for accepting or rejecting data observed by a Bowen ratio system 总被引：1，自引：0，他引：1 
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下载免费PDF全文 The Bowen ratio energy balance method often produces extremely inaccurate magnitudes of the flux due to resolution limits of the instruments. We analysed the criteria used for rejecting inaccurate data observed using a Bowen ratio system and the resolution limit of the sensors to analytically determine the reliable values of the Bowen ratio (β) and the latent and sensible heat fluxes. The formula used to calculate the error limit of the Bowen ratio (β) was corrected based on the theory of error analysis. An example was proposed for the common case with 0.2 °C resolution limit of temperature measurement and 0.08 kPa resolution limit of water vapour pressure measurement, to show the steps of accepting or rejecting data observed by a Bowen ratio system. The acceptance or rejection of data observed by a Bowen ratio system is a dynamic process, which should be performed based on the excluded interval of the Bowen ratio and the qualitative relationships among the data observed by a Bowen ratio system. The excluded interval of the Bowen ratio can be structured based on the accuracy of the sensors used. Data are excluded first if they do not satisfy the qualitative relationships between the vapour pressure difference, the temperature difference, Bowen ratio, and the available energy, whereas the data in the rejection region range of the Bowen ratio are excluded second. It is necessary to improve the accuracy of the temperature and humidity probes to improve the acceptance rate for data collected using the Bowen ratio system, apart from improving the observed precision of available energy. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
18.
本文以能量守恒原理和边界层梯度输送理论为基础,应用Monin-Obukhov相似函数计算蒸发皿水面感、潜热通量,参数化蒸发皿侧壁热传输能量,建立了一个单层的20 cm蒸发皿蒸发模型.之后利用"古浪非均匀近地层观测试验"中连续14天观测的每小时20 cm蒸发皿数据对所建模型进行检验.研究分析结果表明:模型能够很好地反映蒸发皿水面与地表之间所形成的非均匀性,合理地概括蒸发皿与周围环境之间的相互作用和蒸发皿蒸发的物理过程.另外,模型成功模拟了蒸发皿蒸发的日变化过程,模拟的日蒸发量均方根误差(RMSE)和平均相对误差(MRER)分别为0.44 mm·d-1和3.7%,日蒸发量观测值与模拟值的相关系数为0.998. 相似文献
19.
Shuko Hamada Takeshi Ohta Tetsuya Hiyama Takashi Kuwada Atsuhiro Takahashi Trofim C. Maximov 《水文研究》2004,18(1):23-39
Seasonal changes in the water and energy exchanges over a pine forest in eastern Siberia were investigated and compared with published data from a nearby larch forest. Continuous observations (April to August 2000) were made of the eddy‐correlation sensible heat flux and latent heat flux above the canopy. The energy balance was almost closed, although the sum of the turbulent fluxes sometimes exceeded the available energy flux (Rn ? G) when the latent heat flux was large; this was related to the wind direction. We examined the seasonal variation in energy balance components at this site. The seasonal variation and magnitude of the sensible heat flux (H) was similar to that of the latent heat flux (λE), with maximum values occurring in mid‐June. Consequently, the Bowen ratio was around 1·0 on many days during the study period. On some clear days just after rainfall, λE was very large and the sum of H and λE exceeded Rn ? G. The evapotranspiration rate above the dry canopy from May to August was 2·2 mm day?1. The contributions of understory evapotranspiration (Eu) and overstory transpiration (Eo) to the evapotranspiration of the entire ecosystem (Et) were both from 25 to 50% throughout the period analysed. These results suggest that Eu plays a very important role in the water cycle at this site. From snowmelt through the tree growth season (23 April to 19 August 2000), the total incoming water, comprised of the sum of precipitation and the water equivalent of the snow at the beginning of the melt season, was 228 mm. Total evapotranspiration from the forest, including interception loss and evaporation from the soil when the canopy was wet, was 208–254 mm. The difference between the incoming and outgoing amounts in the water balance was from +20 to ?26 mm. The water and energy exchanges of the pine and larch forest differed in that λE and H increased slowly in the pine forest, whereas λE increased rapidly in the larch forest and H decreased sharply after the melting season. Consequently, the shape of the Bowen ratio curves at the two sites differed over the period analysed, as a result of the differences in the species in each forest and in soil thawing. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Satoru Takanashi Yoshiko Kosugi Shinjiro Ohkubo Naoko Matsuo Makoto Tani Abdul Rahim Nik 《水文研究》2010,24(4):472-480
We measured the fluxes of sensible and latent heat between a low‐land dipterocarp forest in Peninsular Malaysia and the atmosphere. No clear seasonal or interannual changes in latent heat flux were found from 2003 to 2005, while sensible heat flux sometimes fluctuated depending on the fluctuation of incoming radiation between wet and dry seasons. The evapotranspiration rates averaged for the period between 2003 and 2005 were 2·77 and 3·61 mm day?1 using eddy covariance data without and with an energy balance correction, respectively. Average precipitation was 4·74 mm day?1. Midday surface conductance decreased with an increasing atmospheric water vapour pressure deficit and thus restricted the excess water loss on sunny days in the dry season. However, the relationship between the surface conductance and vapour pressure deficit did not significantly decline with an increase in volumetric soil water content even during a period of extremely low rainfall. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献