近地层能量平衡闭合问题——综述及个例分析

近地层能量闭合问题,即测量到的感热和潜热通量之和一般总小于近地层可利用能量(净辐射与土壤热通量之差),是近20年来困扰地气相互作用实验研究的主要难点之一。对国内外有关研究现状做了综述,与解决此问题日益迫切的要求相适应,问题的实质及解决途径近年来已逐渐明朗。"涡动相关方法"应用在复杂的大气湍流通量观测中的局限,特别是对低频较大尺度湍流通量的低估,仍是关键所在。在理论分析的基础上,结合2008年部分"黑河综合实验"资料对有关计算结果做了具体介绍。以阿柔站6天连续资料为例,仔细计算土壤浅层热储存,在涡动相关资料再处理中加上高低频损失修正等,再参考该站大口径闪烁仪(LAS)观测对感热通量的提高,能量闭合率可达到99%,当然这只是个例。许多复杂情况下,较大尺度的涡旋或湍流有组织结构(TOS)会有更明显影响。近地层能量闭合问题的根本解决必须考虑后者的贡献,提高通量观测的时空代表性。     

不同土壤热通量测算方法的比较及其对地表能量平衡闭合影响的研究

土壤热通量是地表能量平衡的重要分量,对其测算方法的研究对理解能量平衡过程具有十分重要的意义.利用2010年馆陶站土壤热通量等相关观测数据对多种测算土壤热通量的方法:实测土壤热通量和热储存量的结合方法(PlateCal)、热传导方程校正法(TDEC)、谐波分析法(HM)、平均土壤热电偶法(TCAV)、耦合热传导—对流法(ITCC)获取的地表土壤热通量进行了对比分析,并且采用最优方法计算馆陶站2008-2010年的地表土壤热通量,分析了该站土壤热通量日、季节变化特征.主要结论如下:①PlateCal和TDEC法分别为获取土壤热通量的最优观测与计算方法,而HM,TCAV和ITCC法计算结果均不理想;②PlateCal与TDEC法对地表土壤温度均不敏感,而HM法对地表土壤温度则比较敏感,各种地表土壤热通量的观测与计算方法均对土壤湿度敏感;③馆陶站冬小麦、玉米覆盖地表及地表裸露时期的地表土壤热通量均呈现典型的日、季节变化特征,与净辐射变化趋势一致;④考虑热储存后,可将馆陶站2010年各月地表能量闭合率提高4％～11％,对2008-2010年的年能量平衡闭合率提高3％～5％.     

基于涡度相关技术估算植被/大气间净CO2交换量中的不确定性

近年来，涡度相关技术的进步使陆地生态系统CO2通量的长期和连续观测成为可能。目前，涡度相关技术是全球通量观测网络（FLUXNET）测定植被/大气间CO2通量的主要技术手段，但绝大部分CO2通量观测站点都处于非典型的理想条件下，不能完全满足涡度相关技术的基本假设条件，从而导致基于涡度相关技术估算植被/大气间净生态系统CO2交换量的不确定性。系统介绍了涡度相关技术的基本假设，基本理论公式和误差的类型与特征等理论问题，重点阐述了通量测定中仪器本身的物理限制、二维和三维的气流运动、数据处理的方法和夜间通量的低估等不确定性的主要来源，并据此对通量观测研究中需要优先考虑的问题提出一些建议。研究认为数据质量控制与分析以及误差评价是不同通量站点间的结果比较和全球尺度综合分析的过程中需重点考虑的问题。     

基于动三轴试验的层间错动带动孔压特性及能量分析

2008年汶川地震触发的大光包滑坡滑带形成背景是渗水层间错动带,该带强度变化是决定滑坡启动的主要因素,动孔压发展是土体材料强度劣化的根本原因,故基于系列室内动三轴试验研究该带材料孔压特性。结果表明,动载下层间错动带材料孔压快速增长,循环剪应力比越大,孔压增长越快,不同荷载条件下应变达到5%时动孔压比等于1,材料液化,根据动孔压比与振次比曲线的拟合关系提出幂函数应力模型。从能量角度描述层间错动带材料孔压增长特性,揭示出循环剪应力比对累积能量耗损与动孔压比曲线影响较小而围压对其影响较大,并进一步提出孔压增长的能量模型。     

青藏高原多年冻土区地表能量收支过程及其对活动层影响的初步分析

基于2005—2016年青藏高原多年冻土区唐古拉和西大滩站的气象、涡动通量以及活动层资料,利用涡动相关法、气象梯度法和SHAW模型等方法探究了气候变化背景下高原多年冻土区地表能量通量变化规律及其对活动层的影响。结果表明：2005—2016年唐古拉和西大滩气温、地气温差有所升高,年降水量、10 cm土壤含水量及风速有所下降。2005年以来唐古拉和西大滩净辐射（R_n ）与感热（H）呈增加趋势,潜热（LE）呈减小趋势,地表土壤热通量（G）变化较小。唐古拉和西大滩地表能量通量季节变化明显,但受海拔、纬度、坡向、土壤冻融过程、降水、下垫面状况等因素的影响,地表能量通量存在区域差异。研究时段内,唐古拉和西大滩地表冻结指数与土壤热通量呈负相关;融化指数、活动层厚度与土壤热通量呈正相关,融化期间土壤热通量积累量与融化深度的变化呈线性增加关系。     

Limitations and improvements of the energy balance closure with reference to experimental data measured over a maize field

The use of energy fluxes data to validate land surface models requires that energy balance closure conservation is satisfied, but usually this condition is not verified when the available energy is bigger than the sum of turbulent vertical fluxes. In this work, a comprehensive evaluation of energy balance closure problems is performed on a 2012 data set from Livraga obtained by a micrometeorological eddy covariance station located in a maize field in the Po Valley. Energy balance closure is calculated by statistical regression of turbulent energy fluxes and soil heat flux against available energy. Generally, the results indicate a lack of closure with a mean imbalance in the order of 20%. Storage terms are the main reason for the unclosed energy balance but also the turbulent mixing conditions play a fundamental role in reliable turbulent flux estimations. Recently introduced in literature, the energy balance problem has been studied as a scale problem. A representative source area for each flux of the energy balance has been analyzed and the closure has been performed in function of turbulent flux footprint areas. Surface heterogeneity and seasonality effects have been studied to understand the influence of canopy growth on the energy balance closure. High frequency data have been used to calculate co-spectral and ogive functions, which suggest that an averaging period of 30 min may miss temporal scales that contribute to the turbulent fluxes. Finally, latent and sensible heat random error estimations are computed to give information about the measurement system and turbulence transport deficiencies.     

基于SEBS模型和Landsat 8数据的黑河下游蒸散发时空特性分析

对黑河下游地区蒸散发量的估算及其时空特性的研究,有助于进一步了解流域水循环,合理利用水资源,防止生态环境进一步恶化。利用SEBS模型估算了黑河下游额济纳绿洲2014年15天的日蒸散量,将SEBS估算的日蒸散与不同下垫面5个站点的EC实测值进行对比,其均方根误差和确定性系数分别为1.2 mm、0.85（5个站点）,0.5 mm、0.96（2个站点）,表明SEBS模型的结果是合理的,可以适用于黑河下游额济纳绿洲地区的地表蒸散量的估算。同时分析了黑河下游蒸散发的时空变化规律,结果表明,黑河下游额济纳绿洲地区,蒸散发在时间上存在明显的季节变化规律：夏季 > 春季 > 秋季 > 冬季;空间上呈现明显的沿河分布的趋势。不同土地覆被类型蒸散发有相似的季节变化特征,但其季节变化幅度并不相同,规律为：水体 > 耕地 > 灌丛地 > 草地 > 裸土地 > 沙地。     

地下含水层储能两阶段热量运移数值模型研究

为了简单而准确地预测地下含水层储能情况,考虑了地下含水层储能过程时间跨度大、储能保温分阶段的实际特点,分析了地下含水层流动和换热模型物理参数的对比特点,以热平衡和热扩散原理为基础,建立分成两个连续阶段的地下含水层储能数值计算模型.模型求解中,采用控制容积法,以全隐格式进行热扩散方程的离散化,然后应用Jacobi方法迭代求解,模拟结果和实际观测数据吻合很好.该模型还分析了含水层储能循环采灌过程中抽出储能水的温度变化的一般特点.     

基于能量平衡的多年冻土区公路设计理论研究

青藏公路长期研究表明,青藏高原多年冻土公路工程空间效应敏感,主要表现为公路空间效应直接改变下伏冻土地基的天然能量平衡状态,继而引发一系列工程病害. 针对这一工程问题,提出多年冻土地区公路能量平衡设计理论,研究公路工程建设引发的多年冻土地基能量变化状态,平衡自然环境变化和工程建设等导致的外界“有害”能量导入与工程处置措施对冻土地基中“有害”能量导出之间相互关系,从空间和时间两个维度分析多年冻土地区公路工程的能量平衡过程. 据此,作为多年冻土公路工程的设计依据,将为青藏高原高速公路的科学设计提供理论支持.     

基于能量平衡对额尔齐斯河流域融雪过程的研究

为定量描述额尔齐斯河流域积雪的消融过程,建立了利用基于能量平衡的积雪模型,对流域内库威积雪站2014年1月4日-3月28日积雪的积累和消融过程进行了模拟.结果表明:模型能够很好的模拟出融雪期净辐射能量的变化过程,对雪水当量的模拟结果也非常好,雪水当量的观测值和模拟值之间的Nash系数达到了0.989.在积雪的积累期,雪表的净辐射、感热、潜热通量的绝对值以及地表热通量明显低于积雪的消融期.在积累期,感热和潜热通量以及土壤热通量受到雪层厚度的影响.当雪水当量小于10 mm时,感热和潜热通量的绝对值偏高,土壤热通量的波动性也偏大.在积累期积雪的物质损失全部为升华损失,升华量为2.74 mm;在消融期,积雪的融化量为66.26 mm,升华量为2.04 mm.净辐射对积雪物质损失的贡献达到了83.1%,湍流通量对积雪物质损失的贡献达到16.9%.由于在融化期土壤热通量为正值,因此土壤热通量对融雪没有贡献.     

基于能量平衡法的黑河中游灌溉渠道蒸发量估算

干旱区绿洲农田需要通过渠道引水进行灌溉,在此过程中蒸发损失不可避免,尤其是在渠系广泛分布的情况下,蒸发损失量大,如何估算这部分量对于干旱区水资源管理至关重要. 以甘肃张掖绿洲灌溉渠道为研究对象,采用Mihara所提供的基于能量平衡理论的经验方程,对渠道蒸发量进行了估算.结果表明：蒸发率在晴天时白天大于夜间,阴天时白天和夜间相差不大,气温和相对湿度是影响蒸发率的主要因子.累计蒸发量在晴天时白天是夜间的2倍左右,阴天时白天和夜间相差不大,蒸发率是直接原因.     

Numerical analysis of seasonal heat storage in an energy pile foundation

The use of concrete geostructures for energy extraction and storage in the ground is an environmentally friendly and easy way of cooling and heating buildings. With such energy geostructures, it is possible to transfer energy from the ground to buildings by means of fluid-filled pipes cast in concrete. By injecting thermal energy in summer and extracting it in winter, the ground in the area of a building’s piles can be used for seasonal energy storage, as long as the underground water flow in the storage remains low. This paper is a contribution to the improvement of the knowledge in the field of energy geostructures. The behaviour of a multi-pile seasonal storage system subjected to thermo-mechanical loading is examined numerically from both thermal and mechanical perspectives. The purpose of this paper is (i) to propose a thermo-hydro-mechanical 2D solution to the 3D problem, (ii) to explore the thermal behaviour of this type of storage and (iii) to evaluate its structural consequences. Coupled multi-physical finite element modelling is conducted. The efficiency of the storage is not dramatically affected by an increase in the annual mean temperature of the storage. It is shown that induced mechanical loads are less important when considering a wholly heated pile structure than when considering a single heated pile in a foundation. The evolution of stresses in the piles and in the soil during heating–cooling cycles also reveals possible critical phenomena.     

三江平原典型沼泽湿地能量平衡和蒸散发研究

基于涡度相关技术对三江平原典型沼泽湿地的水热通量进行了连续观测,研究沼泽湿地能量平衡和蒸散发的季节变化,确定观测期内沼泽湿地总蒸散量,并通过逐步回归方程估算沼泽湿地水面蒸发和植被蒸腾。结果表明,沼泽湿地的能量平衡具有明显的季节变化特征,总体看来,潜热通量是湿地的主要能量支出项,占净辐射的45.5%,感热通量和存储热通量分别占净辐射的27.9%和26.7%。2006年5~10月份沼泽湿地总蒸散量为310.6mm,月均日蒸散量最高值出现在7月。观测期内沼泽湿地水面蒸发量约为221mm,占总蒸散量的71%左右,植被蒸腾量则约占总蒸散量的29%,湿地蒸散发以水面蒸发为主。     

Surface energy balance of seasonal snow cover for snow-melt estimation in N-W Himalaya

This study describes time series analysis of snow-melt, radiation data and energy balance for a seasonal snow cover at Dhundi field station of SASE, which lies in Pir Panjal range of the N-W Himalaya, for a winter season from 13 January to 12 April 2005. The analysis shows that mean snow surface temperature remains very close to the melting temperature of snow. It was found close to −1°C for the complete observational period which makes the snow pack at Dhundi moist from its beginning. The average air temperature over this period was found to be 3.5°C with hourly average variation from −5.5°C to 13°C. The snow surface at this station received a mean short wave radiation of 430W m⁻², out of which 298W m⁻² was reflected back by the snow surface with mean albedo value of 0.70. The high average temperature and more absorption of solar radiation resulted in higher thermal state of the snowpack which was further responsible for faster and higher densification of the snowpack. Net radiation energy was the major component of surface energy budget with a mean value of 83W m⁻². Bulk transfer model was used to calculate turbulent fluxes. The net energy was utilized for satisfying cold content and snow-melt by using measured snow surface temperature and density of snow pack. The mean square error between calculated and measured daily snow-melt was found to be approximately 6.6mm of water equivalent.     

Transitions in the surface energy balance during the life cycle of a monsoon season

In this observational/diagnostic study, we illustrate the time history of some important parameters of the surface energy balance during the life cycle of a single monsoon season. This chronology of the surface energy balance portrays the differential equilibrium state from the preonset phase to the withdrawal phase. This includes an analysis of the time history of base variables such as soil moisture, ground temperature, cloud cover, precipitation and humidity. This is followed by an analysis of the components of the surface energy balance where we note subtle changes in the overall balances as we proceed from one epoch of the monsoon to the next. Of interest here is the transition sequence: preonset, onset, break, revival, break, revival and withdrawal during the year 2001. Computations are all illustrated for a box over central India where the coastal effects were small, data coverage was not sparse and where the semi-arid land mass changes drastically to a lush green area. This region exhibited large changes in the components of surface energy balance. The principal results pertain to what balances the difference among the incoming short wave radiation (at the earth’s surface) and the long wave radiation exhibited by the ground. That difference is balanced by a dominant sensible heat flux and the reflected short wave radiation in the preonset stage. A sudden change in the Bowen ratio going from>1 to <1 is noted soon after the onset of monsoon. Thereafter the latent heat flux from the land surface takes an important role and the sensible heat flux acquires a diminishing role. We also examine the subtle changes that occur in the components of surface energy balance between the break and the active phases. The break phases are seen to be quite different from the preonset phases. This study is aimed to illustrate the major importance of moisture and clouds in the radiative transfer computations that are central to the surface energy balance during each epoch. These sensitivities (of moisture and clouds) have major consequences for weather and climate forecasts