南极瑞穗站雪面热量平衡特征

利用南极瑞穗站(日本)1979年近地面层微气象资料及净辐射、本站气压等资料进行了统计分析。采用鲍文比-能量平衡法求得月平均感热通量和潜热通量,采用热含法计算得出月平均雪面热通量,使用了直接测量的净辐射通量,研究了该站雪面热量平均特征。其中突出的特征是3—12月雪面净辐射值为负值,主要靠感热通量由大气向雪面补充热量。将本文结果与苏联少先队站1956年的结果进行了比较,得出相当一致的年变化规律。最后,得出瑞穗站雪面为一强冷源。     

Simulation of snow processes beneath a boreal scots pine canopy

A physically-based multi-layer snow model Snow-Atmosphere-Soil-Transfer scheme(SAST)and a land surface model Biosphere-Atmosphere Transfer Scheme(BATS)were employed to investigate how boreal forests influence snow accumulation and ablation under the canopy.Mass balance and energetics of snow beneath a Scots pine canopy in Finland at different stages of the 2003-2004 and 2004 2005 snow seasons are analyzed.For the fairly dense Scots pine forest,drop-off of the canopy-intercepted snow contributes,in some cases,twice as much to the underlying snowpack as the direct throughfall of snow.During early winter snow melting,downward turbulent sensible and condensation heat fluxes play a dominant role together with downward net longwave radiation.In the final stage of snow ablation in middle spring,downward net all- wave radiation dominates the snow melting.Although the downward sensible heat flux is comparable to the net solar radiation during this period,evaporative cooling of the melting snow surface makes the turbulent heat flux weaker than net radiation.Sensitivities of snow processes to leaf area index(LAI)indicate that a denser canopy speeds up early winter snowmelt,but also suppresses melting later in the snow season. Higher LAI increases the interception of snowfall,therefore reduces snow accumulation under the canopy during the snow season;this effect and the enhancement of downward longwave radiation by denser foliage outweighs the increased attenuation of solar radiation,resulting in earlier snow ablation under a denser canopy.The difference in sensitivities to LAI in two snow seasons implies that the impact of canopy density on the underlying snowpack is modulated by interannual variations of climate regimes.     

Energy Balance Of A Sparse Coniferous High-Latitude Forest Under Winter Conditions

Measurements carried out in Northern Finland on radiation and turbulent fluxes over a sparse, sub-arctic boreal forest with snow covered ground were analysed. The measurements represent late winter conditions characterised by low solar elevation angles. During the experiment (12–24 March 1997) day and night were about equally long. At low solar elevation angles the forest shades most of the snow surface. Therefore an important part of the radiation never reaches the snow surface but is absorbed by the forest. The sensible heat flux above the forest was fairly large, reaching more than 100 W m^-2. The measurements of sensible heat flux within and above the forest revealed that the sensible heat flux from the snow surface is negligible and the sensible heat flux above the forest stems from warming of the trees. A simple model for the surface energy balance of a sparse forest is presented. The model treats the diffuse and direct shortwave (solar) radiation separately. It introduces a factor that accounts for the shading of the ground at low solar elevation angles, and a parameter that deals with the partial transparency of the forest.Input to the model are the direct and diffuse incoming shortwave radiation.Measurements of the global radiation (direct plus diffuse incoming shortwaveradiation) above the forest revealed a considerable attenuation of the globalradiation at low solar elevation. A relation for the atmospheric turbidity asfunction of the solar elevation angle is suggested. The global radiation wassimulated for a three month period. For conditions with a cloud cover of lessthan 7 oktas good agreement between model predictions and measurementswere found. For cloud cover 7 and 8 oktas a considerable spread can beobserved. To apply the proposed energy balance model, the global radiationmust be separated into its diffuse and direct components. We propose a simpleempirical relationship between diffuse shortwave and global radiation asfunction of cloud cover.     

植被覆盖异常变化影响陆面状况的数值模拟

利用NCAR最新的公用陆面模式CLM3．0，通过数值模拟初步研究了植被叶面积指数（LAI，leafareaindex）异常变化对陆面状况的可能影响，结果表明，植被LAI的异常变化能够引起地表能量平衡、地表水循环等陆面状况的异常。（1）植被LAI的异常变化主要影响太阳辐射在植被与地表之间的分配，以及地表的感热、潜热通量。植被LAI增大，能够引起植被吸收的太阳辐射增加，而到达土壤表面的太阳辐射减小，并导致植被的蒸发、蒸腾潜热通量增加，造成地表的蒸发潜热和感热通量不同程度的减小。（2）植被LAI增大时，植被对降水的拦截和植被叶面的蒸发增大，植被的蒸腾作用也明显增强；植被LAI增加会使得热带地区各个季节的土壤表面蒸发、地表径流减小，而土壤湿度有所增加；LAI增加造成中高纬度地区土壤蒸发的减少主要出现在夏季；LAI增加还能够引起中高纬地区冬、春积雪深度不同程度的增加，造成春末、夏初地表径流的增加。（3）植被LAI增加能够使得叶面和土壤温度有所下降，但植被LAI的变化对叶面、土壤温度的影响相对较小。     

基于常规气象资料融雪模式的建立及应用

以能量平衡方程为基础,考虑太阳短波辐射、大气和地面的长波辐射、潜热、感热传输以及下垫面的热传导等能量之间的平衡,建立了利用常规气象观测资料预测雪面温度和积雪深度变化的融雪模型。利用2009年1—3月以及2009年12月—2010年1月在湖北恩施雷达站的积雪观测数据进行模拟和验证,结果表明：该模型对于雪面温度和积雪深度都有较好的模拟效果。当下垫面导热系数λg〈0.5时,下垫面对雪深的影响很小;当λg≥0.5时,积雪融化速度随λg的增大而加快,说明下垫面的热传导是影响积雪深度变化的主要因素之一。     

Boreal forest and tundra ecosystems as components of the climate system

The effects of terrestrial ecosystems on the climate system have received most attention in the tropics, where extensive deforestation and burning has altered atmospheric chemistry and land surface climatology. In this paper we examine the biophysical and biogeochemical effects of boreal forest and tundra ecosystems on atmospheric processes. Boreal forests and tundra have an important role in the global budgets of atmospheric CO₂ and CH₄. However, these biogeochemical interactions are climatically important only at long temporal scales, when terrestrial vegetation undergoes large geographic redistribution in response to climate change. In contrast, by masking the high albedo of snow and through the partitioning of net radiation into sensible and latent heat, boreal forests have a significant impact on the seasonal and annual climatology of much of the Northern Hemisphere. Experiments with the LSX land surface model and the GENESIS climate model show that the boreal forest decreases land surface albedo in the winter, warms surface air temperatures at all times of the year, and increases latent heat flux and atmospheric moisture at all times of the year compared to simulations in which the boreal forest is replaced with bare ground or tundra. These effects are greatest in arctic and sub-arctic regions, but extend to the tropics. This paper shows that land-atmosphere interactions are especially important in arctic and sub-arctic regions, resulting in a coupled system in which the geographic distribution of vegetation affects climate and vice versa. This coupling is most important over long time periods, when changes in the abundance and distribution of boreal forest and tundra ecosystems in response to climatic change influence climate through their carbon storage, albedo, and hydrologic feedbacks.     

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。     

The Influence of Changes in Vegetation Type on the Surface Energy Budget

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卫星遥感确定沙特阿拉伯吉达地区非均匀地表区域地表参数和能量通量

对临海沙漠地区非均匀地表区域地表能量通量和蒸发(蒸散)的研究,是一个十分重要但又是一个难点问题。本文提出了1个基于卫星遥感和地面观测的参数化方案,并把其应用于沙特阿拉伯吉达地区,利用1个景的陆地资源卫星Landsat-7E^TM^ 资料进行了分析研究,得到了一些有关临海沙漠地区非均匀地表区域地表特征参数、植被参数和地表能量通量的新概念。最后讨论了所提出的参数化方案的适用范围和需改进之处。     

宁南退耕还草区近地面的湍流通量特征研究

根据Monin—Obukhov相似性理论，运用空气动力学方法和能量平衡法，结合2002—2003年小气候资料，分别分析了宁夏南部山区（下称宁南）退耕还草区湍流通量和地表通量（净辐射、感热、潜热和土壤热通量）的分布和季节变化特征，为宁南退耕还草区陆面过程的认识、数值模拟和气候分析提供理论参考依据。     

甘肃马衔山区陆面过程与降水的研究

采用定西的麦田微气象观测,定西、兰州的辐射观测和马衔山区34个气象、水文和雨量站的气候资料,结合NOAA-16卫星的AVHRR资料以及反演的地表植被盖度和反射率,并用SEBAL算法推导出夏季地表净辐射、感热、潜热、土壤热通量密度的区域分布特征,并分析陆面过程对降水的影响。结果表明:本区降水的空间分布与夏季植被盖度对应最好,相关系数高达0.722,其次是土壤热通量和潜热通量,相关系数分别为-0.65和0.615。这表明森林通过降低地表反射率和表面温度,不仅增加地表净辐射,而且减少其用于感热和土壤热通量的消耗。由于林区地表水分多,从而将接收较多的太阳辐射能主要用于蒸散,增加边界层中的水汽。故林区降水远大于植被稀疏的半干旱黄土梁。     

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     

乾安地区盐碱地显热通量的测量

文中给出了用大孔径闪烁仪在 2 0 0 0年生长季观测到的盐碱地区显热通量的主要结果 ,并初步计算了当地的水热平衡状况。结果表明 :乾安盐碱地区显热通量占净辐射量的百分比在干旱、非生长季达到 6 5 % ,在多雨、植被生长季仅为 11% ;显热通量因降水而明显降低 ,幅度与降水强度有关 ,反映了当地的气候和土壤特征。文中还把LAS的测量结果与传统的梯度法作了比较 ,结果基本一致。     

Impact of the snow cover scheme on snow distribution and energy budget modeling over the Tibetan Plateau

This paper presents the impact of two snow cover schemes (NY07 and SL12) in the Community Land Model version 4.5 (CLM4.5) on the snow distribution and surface energy budget over the Tibetan Plateau. The simulated snow cover fraction (SCF), snow depth, and snow cover days were evaluated against in situ snow depth observations and a satellite-based snow cover product and snow depth dataset. The results show that the SL12 scheme, which considers snow accumulation and snowmelt processes separately, has a higher overall accuracy (81.8%) than the NY07 (75.8%). The newer scheme performs better in the prediction of overall accuracy compared with the NY07; however, SL12 yields a 15.1% underestimation rate while NY07 overestimated the SCF with a 15.2% overestimation rate. Both two schemes capture the distribution of the maximum snow depth well but show large positive biases in the average value through all periods (3.37, 3.15, and 1.48 cm for NY07; 3.91, 3.52, and 1.17 cm for SL12) and overestimate snow cover days compared with the satellite-based product and in situ observations. Higher altitudes show larger root-mean-square errors (RMSEs) in the simulations of snow depth and snow cover days during the snow-free period. Moreover, the surface energy flux estimations from the SL12 scheme are generally superior to the simulation from NY07 when evaluated against ground-based observations, in particular for net radiation and sensible heat flux. This study has great implications for further improvement of the subgrid-scale snow variations over the Tibetan Plateau.     

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。     

陆面过程对全球变暖的响应及可能机制—基于CMIP3的多模式集合分析

利用“国际耦合模式比较计划” (Phase 3 of the Coupled Model Intercomparison Project, CMIP3) 12个模式对20世纪 (The Twentieth-Century Climate in Coupled Models, 20C3M) 和21世纪SRES (Special Report on Emissions Scenarios) A1B 情景下的模拟结果, 通过21世纪 (2001～2099年) 与20世纪 (1901～1999年) 陆面能量和水文变量的对比分析, 揭示了陆面过程对全球变暖响应的基本特征, 并探讨了其可能的响应机制。结果表明, 与20世纪相比, 21世纪全球陆面平均的表面温度、 地表净辐射、 潜热通量明显增加; 而感热通量有所减小。降水、 径流、 蒸发等地表水循环分量也表现出不同程度的增加, 而土壤含水量有减小趋势。通过分析近地层主要大气强迫变量与陆面变量之间的联系, 发现陆面能量平衡过程对全球变暖的响应主要受向下长波辐射和气温变化的影响, 而温度的变化对陆面水文过程的影响起决定性的作用。进一步分析表明, 陆面过程对全球变暖的响应存在明显的区域性差异, 陆面温度和感热对全球变暖响应最显著的区域位于北半球中高纬, 而净辐射和潜热对全球变暖的响应在亚洲中部和非洲大陆最显著。相对于20世纪, 21世纪主要是长波辐射和温度对陆面能量平衡过程的贡献重要。对于陆面水文过程, 径流和土壤含水量对全球变暖的响应在亚洲中部以及北美最显著。在全球变暖背景下, 21世纪相对于20世纪, 温度对陆面水循环的影响更加显著, 主要体现在北半球中纬度地区。     

陆面过程模式对土壤含水量初值的敏感性研究

利用IAP94陆面过程模式,采用淮河流域能量与水份循环试验(HUBEX)期间两种下垫面(森林和旱田)、不同季节(5月、8月和11月)的观测资料,研究了模式对土壤含水量初值的敏感性.结果表明:对于森林和旱田下垫面,当土壤含水量减少时,地表净辐射均略有减少,同时潜热通量减少而感热通量增加.另外,模式对土壤含水量初值的敏感性有较明显的季节差异,相对而言在晚春和夏季较强,而在秋季明显减弱.这说明春夏季节的土壤含水量初值在淮河流域区域气候的模拟和预测中尤其值得关注.     

宁夏南部地表辐射和热量平衡的遥感研究

为了研究和揭示宁夏南部地气能量传输过程及特点并进一步评估退耕还林还草的生态效应, 利用Landsat-7 ETM+卫星遥感资料所求取的地表特征参数, 将地表分成水体、裸地、半裸地、草地、林地5类地表覆盖类型, 结合常规气象观测资料, 分别计算得出宁夏南部地表辐射和热量平衡各量的区域分布, 并给出各量的分布图和直方图, 分类别讨论了地表辐射和热量平衡各量分布特征, 使得对宁夏南部区域地表辐射和热量平衡区域分布有一个直观、综合的了解和认识。研究表明, 植被分布对地表辐射和热量平衡各量影响很大。     

The Surface Energy Budget and Its Impact on the Freeze-thaw Processes of Active Layer in Permafrost Regions of the Qinghai-Tibetan Plateau

The surface energy budget is closely related to freeze-thaw processes and is also a key issue for land surface process research in permafrost regions.In this study,in situ data collected from 2005 to 2015 at the Tanggula site were used to analyze surface energy regimes,the interaction between surface energy budget and freeze-thaw processes.The results confirmed that surface energy flux in the permafrost region of the Qinghai-Tibetan Plateau exhibited obvious seasonal variations.Annual average net radiation(R_n)for 2010 was 86.5 W m^-2,with the largest being in July and smallest in November.Surface soil heat flux(G₀)was positive during warm seasons but negative in cold seasons with annual average value of 2.7 W m^-2.Variations in R_n and G₀ were closely related to freeze-thaw processes.Sensible heat flux(H)was the main energy budget component during cold seasons,whereas latent heat flux(LE)dominated surface energy distribution in warm seasons.Freeze-thaw processes,snow cover,precipitation,and surface conditions were important influence factors for surface energy flux.Albedo was strongly dependent on soil moisture content and ground surface state,increasing significantly when land surface was covered with deep snow,and exhibited negative correlation with surface soil moisture content.Energy variation was significantly related to active layer thaw depth.Soil heat balance coefficient K was>1 during the investigation time period,indicating the permafrost in the Tanggula area tended to degrade.