东帕米尔高原地表辐射收支及地表反照率特征

利用东帕米尔高原塔什库尔干国家基本气候站2020年6月至2021年6月观测的辐射数据,分析了东帕米尔高原不同时间尺度和不同天气条件下各辐射通量及地表反照率变化特征。结果表明：（1）各辐射通量在逐日均值变化上呈“V”型曲线;向下短波辐射、向上短波辐射、向下长波辐射、向上长波辐射和净辐射年曝辐量分别为5001.6, 1370.3, 6090.7, 8550.8和1189.0 MJ·m-2;在季节尺度上,各辐射通量总体表现为夏季>春季>秋季>冬季,而向上短波辐射在冬季最高。（2）不同天气下,辐射通量也不同,晴天时,各辐射通量变化均为较平滑的单峰型,少云、多云时均为不规则单峰型,降水时,除冬季外均为多峰型,辐射通量均值变化表现为晴天>少云>多云>降水。（3）地表反照率在观测期间平均值为0.29,最大值出现在1月,最小值出现在7月,分别为0.58和0.24;在季节上表现为冬季最大,夏季最小;春、夏、秋季地表反照率呈“U”型,冬季为倒“U”型;降雨时地表反照率下降,降雪时则地表反照率上升,说明不同降水类型对地表反照率影响不同。     

陆面模拟中植被辐射传输参数化方案研究

在冠层二流辐射传输模式基础上新发展了一个描述太阳短波辐射在植被中传输的冠层四流辐射传输模式.冠层四流辐射传输模式是在大气辐射传输理论的基础上得到一组描述短波辐射在植被中传输过程的冠层辐射传输基本方程,引进大气中求解辐射传输方程的四流近似解法,并求得冠层四流辐射传输方程的解析解.方程中各项参量能够反映叶子或冠层特殊的几何和光学特征.冠层向上、向下辐射通量取决于冠层散射相函数、叶子在入射光方向投影面积、单个叶子反射率和透射率、叶面积指数以及直射光入射太阳高度角等.四流模式计算叶子水平倾角时对太阳短波辐射的反照率,与二流模式结果比较可以验证模式的理论推导和建模都是正确的:计算结果的比较,表明四流模式在水平叶角分布时计算的冠层反照率与二流模式结果一致,同时直射光从任何太阳高度角入射的冠层反照率结果也一致,从而证明发展的冠层四流辐射传输模式是成功的.模拟试验中将两种模型同时耦合到同一个陆面过程模式中进行比较试验,结果表明,冠层四流辐射传输模式能够得到更精确的植被反照率,从而使得陆面模式计算的地表吸收的净太阳辐射通量更接近于观测值.     

疏勒河上游流域多年冻土区辐射变化分析

利用2008年7月-2010年10月祁连山区西段疏勒河上游流域多年冻土区苏里梯度观测系统的辐射数据,分析了该区域的辐射变化特征.结果表明,向下短波辐射、向下和向上长波辐射、净辐射月总量季节性变化明显,冬、春季较小,夏、秋季较大;向上短波辐射月总量的季节变化不明显.日平均向下短波辐射、向下和向上长波辐射有明显的季节变化,1月或12月达到最小值,6月或7月达到峰值;1-3月和12月日平均向上短波辐射振幅变化较小,而4月和10月则变化较大.净辐射日变化冬、春季较小,且振幅也较小,夏、秋季较大,且振幅也较大;辐射四分量的日变化都呈单峰型.生长季节的地表反照率较小,非生长季较大;每年10月地表反照率的日平均变化起伏较大,日变化基本呈“U”形,早晚高、中午低.     

青藏高原不同地区辐射特征对比分析

利用"全球协调加强观测计划(CEOP)之亚澳季风青藏高原试验"(CAMP/Tibet)在藏北高原的BJ站、NPAM站及中国科学院珠穆朗玛峰大气与环境综合观测研究站、纳木错多圈层相互作用综合观测研究站和藏东南高山环境综合观测研究站2007年的辐射观测资料,分析了这些地区不同下垫面地表辐射各分量及地表反照率的日变化和月际变化特征。结果表明,向下短波辐射受太阳高度角的影响存在明显的日变化和月际变化;向上短波辐射的月际变化基本与总辐射一致,在个别月份由于高原积雪造成地表反照率较高,从而使晴天向上短波辐射全年较高;向下长波辐射存在基本的季节变化,最大值出现在天空总云量较多的夏季(6～8月),最小值出现在冬季(12月和1月);向上长波辐射基本上都是夏季为全年最大,冬季为全年最小。这与地表温度的年变化情况相一致。高原不同地区各季节晴天地表净辐射存在差异,NPAM站和藏东南站由于下垫面植被覆盖较好,净辐射值各季节均高于其它各站;NPAM站、纳木错站和珠峰站地表反照率日变化曲线呈"U"型,BJ站和藏东南站日变化相对复杂,藏东南站全年月平均地表反照率较小且变化不大,其他各站存在基本的年变化趋势。     

新疆东部黑戈壁地表辐射及能量收支演变特征

新疆东部黑戈壁作为气候恶劣、人迹罕至的生态脆弱区，具有丰富的太阳能资源。利用红柳河陆气相互作用观测站2019年4、7、9月观测资料，分析东疆黑戈壁地表辐射及能量收支演变特征。结果表明：（1）地表辐射及能量收支各分量日变化均为单峰型。就不同季节而言，太阳总辐射和净辐射为夏季>春季>秋季，反射短波辐射为春季>夏季>秋季，地表和大气长波辐射为夏季>秋季>春季。（2）能量收支各分量季节变化明显，感热通量为春季>夏季>秋季，潜热通量为夏季>秋季>春季，地表土壤热通量为秋季>夏季>春季；能量分配在不同季节均以感热为主，地表土壤热通量次之，潜热通量极其微弱。（3）地表反照率日变化均为“U”型，在不同季节表现为春季>秋季>夏季，依次为0.29、0.27、0.26。东疆黑戈壁地表反照率整体较高，这是下垫面为黑色砾石所致。     

中国天山西部森林积雪短波辐射收支特征

本文通过对中国科学院天山积雪与雪崩研究站不同开阔度森林下积雪表面短波辐射的观测研究，分析了森林积雪短波辐射收支特征，短波辐射透射率。结果表明：阴坡林下积雪表面短波辐射小于阳坡，且随森林开阔度的减小而减小；林下雪面短波辐射和净短波辐射随太阳高度角增加而逐渐增加，不同开阔度林下雪面短波辐射和净短波辐射的差异也随太阳高度角的增加而不断增大；阳坡、阴坡林冠上方和80%开阔度林下积雪短波辐射在晴天日变化呈单峰型，林下积雪短波辐射峰值出现时间由林冠上方直接辐射和散射辐射的相对关系决定；多云天气，短波辐射的日变化特征取决于云量的变化；林冠开阔度越大，其短波辐射率越大，日平均短波辐射透射率随太阳高度角的增加而增加，且开阔度越大，其增加速率越快，短波辐射透射率日变化呈“U”型，早晚大于12:00~17:00。     

阿尔卑斯山杉林冠层影响辐射传输的个例分析

利用瑞士Alptal观测站杉树林冠层上方、下方的辐射观测资料,分析了冠层对短波辐射的减弱及对长波辐射的增幅作用及其季节变化。结果表明,对比较密集的常绿针叶林,冠层对入射短波辐射的透过率随着太阳高度的降低而减小,春季以后趋于稳定;冠层对长波辐射的增幅作用随天气状况而变化,这种增幅作用在晴空条件下最显著,可达1.5倍。在冬季,因为太阳辐射较弱,冠层对长波辐射的增幅作用超过对短波辐射的减弱从而增加地面净辐射。在其它季节,太阳辐射比较强,冠层对短波辐射的减弱超过对长波辐射的增幅作用而减少地面净辐射。地面净辐射与冠层上方气温的变化趋势虽然在有些时段一致,但在伴随降雪过程的降温时段,地面净辐射与气温的变化趋势近乎反相,在积雪融化时段,地面净辐射的增加比气温升高更显著,尤其是在白天。     

基于CERES/Aqua卫星资料的新疆地面短波向下辐射时空分布特征

利用CERES SSF Aqua MODIS Edition 3A数据对新疆地区2003-2015年的13时至17时的地面短波向下辐射变化进行研究,得到了新疆地区近13年的地面短波向下辐射时空分布特征。可以发现,该地区地面短波向下辐射从东南向西北随着纬度的增加而逐渐减少,从春季到冬季,地面短波向下辐射逐渐地由经向分布向纬向分布转变,秋季变化幅度为全年最大,夏季最小。年变化呈现单峰趋势,接近正态分布,最大值出现在2004年5月13时。在日变化中,13时最大。新疆地区近13年整体来说,地面地面短波向下辐射呈现下降趋势,以13.3 W?m-2/10a的速率减小。春季变化呈现增大趋势,其余各季均为减小趋势。     

成都东北部地区太阳辐射特征分析

该文利用2018年1月—12月成都东北部地区的太阳辐射观测资料,分析了辐射能量的收支状况和特征。结果表明:成都东北部地区各辐射分量(除净长波辐射)均是夏季最强,冬季最弱,最大值出现在8月。净长波辐射春季最强,秋季最弱,与空气相对湿度、气温日较差分别成负相关、正相关。净全辐射白天为正值,晚上为负值。成都东北部地区全年有10.7%的太阳短波辐射被地表反射,接收的太阳短波辐射有29.36%被地表以长波辐射的方式释放到大气,对地气系统能量收支的贡献为61.18%。     

东莞市辐射强度特征及影响因子

东莞观测站采用地面辐射基准站网(BSRN)通用的荷兰Kipp & Zonen设备,进行太阳短波辐射和地面、大气长波辐射观测。利用2010年8月—2011年7月的观测数据,用统计分析的方法,得到地面太阳短波辐射和地面、大气长波辐射强度的变化特征,并初步分析了影响辐射强度变化的因子。结果表明,东莞市各月的太阳总辐射平均值呈现单峰值变化,且夏季＞秋季＞春季＞冬季,短波辐射各分量的日变化也呈明显单峰型变化特征;长波辐射的日、月变化趋势较平缓;东莞市全年各月净辐射通量平均值均为正值。云是影响太阳辐射强度变化的显著因子,对直接辐射的衰减更明显,多云天气的总辐射、直接辐射全年平均衰减率分别为11%、34%,阴天总辐射、直接辐射全年平均衰减率分别达到47%、83%。大气透明度对短波辐射和长波辐射强度变化均产生影响,无霾日总辐射、直接辐射、反射辐射强度均比灰霾日强,而散射辐射则较弱,灰霾日的天空长波辐射及地面长波辐射强度稍强于无霾日。还探讨了总辐射观测值与理论值的差异,推测水汽对短波辐射的衰减是造成太阳短波辐射平衡存在差异的原因之一。      

中国地区夏季平均加热率的时空分布特征

The latitude-altitude distributions of radiative fluxes and heating rates are investigated by utilizing CloudSat satellite data over China during summer. The Tibetan Plateau causes the downward shortwave fluxes of the lower atmosphere over central China to be smaller than the fluxes over southern and northern China by generating more clouds. The existence of a larger quantity of clouds over central China reflects a greater amount of solar radiation back into space. The vertical gradients of upward shortwave radiative fluxes in the atmosphere below 8 km are greater than those above 8 km. The latitudinal-altitude distributions of downward longwave radiative fluxes show a slantwise decreasing trend from low latitudes to high latitudes that gradually weaken in the downward direction. The upward longwave radiative fluxes also weaken in the upward direction but with larger gradients. The maximum heating rates by solar radiation and cooling rates by longwave infrared radiation are located over 28-40°N at 7-8 km mean sea level (MSL), and they are larger than the rates in the northern and southern regions. The heating and cooling rates match well both vertically and geographically.     

2011年2月—2012年1月东南极高原辐射平衡观测研究

利用东南极高原熊猫-1自动气象站2011年2月—2012年1月观测的辐射资料和相关资料,对辐射分量和辐射平衡的季节变化进行了研究。结果表明,夏季是东南极高原获得太阳能的主要时段,总辐射通量夏季平均为365.0 W/m²,总量达到2752.1 MJ/m²,占全年总辐射量的58%。各个季节均能出现总辐射瞬时值大于大气顶水平总辐射,春季发生频率最高,冬季最小,总辐射平均日变化呈单峰型。大气长波辐射除夏季外,日变化不明显。冰雪面长波辐射除冬季外,各季节平均日变化呈明显的单峰单谷型。净辐射12月和1月为很小的正值,其他月份为负值。年平均净辐射为 -8.7 W/m²,表明地表相对于大气为冷源。该站的辐射平衡特征与其他南极内陆高原站相似,雪面具有强烈的辐射冷却效应,导致净辐射绝对值都小于下降风区。     

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.     

The Arctic surface energy budget as simulated with the IPCC AR4 AOGCMs

Ensembles of simulations of the twentieth- and twentyfirst-century climate, performed with 20 coupled models for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment, provide the basis for an evaluation of the Arctic (70°–90°N) surface energy budget. While the various observational sources used for validation contain differences among themselves, some model biases and across-model differences emerge. For all energy budget components in the twentieth-century simulations (the 20C3M simulation), the across-model variance and the differences from observational estimates are largest in the marginal ice zone (Barents, Kara, Chukchi Seas). Both downward and upward longwave radiation at the surface are underestimated in winter by many models, and the ensenmble mean annual net surface energy loss by longwave radiation is 35 W/m², which is less than for the NCEP and ERA40 reanalyses but in line with some of the satellite estimates. Incoming solar radiation is overestimated by the models in spring and underestimated in summer and autumn. The ensemble mean annual net surface energy gain by shortwave radiation is 39 W/m², which is slightly less than for the observational based estimates, In the twentyfirst-century simulations driven by the SRES A2 scenario, increased concentrations of greenhouse gasses increase (average for 2080–2100 minus average for 1980–2000 averages) the annual average ensemble mean downward longwave radiation by 30.1 W/m². This was partly counteracted by a 10.7 W/m² reduction in downward shortwave radiation. Enhanced sea ice melt and increased surface temperatures increase the annual surface upward longwave radiation by 27.1 W/m² and reduce the upward shortwave radiation by 13.2 W/m², giving an annual net (shortwave plus longwave) surface radiation increase of 5.8 W/m² , with the maximum changes in summer. The increase in net surface radiation is largely offset by an increased energy loss of 4.4 W/m² by the turbulent fluxes.     

A Multi-layer Radiation Model for Urban Neighbourhoods with Trees

A neighbourhood-scale multi-layer urban canopy model of shortwave and longwave radiation exchange that explicitly includes the radiative effects of tall vegetation (trees) is presented. Tree foliage is permitted both between and above buildings, and mutual shading, emission and reflection between buildings and trees are included. The basic geometry is a two-dimensional canyon with leaf area density profiles and probabilistic variation of building height. Furthermore, the model accounts for three-dimensional path lengths through the foliage. Ray tracing determines the receipt of direct shortwave irradiance by building and foliage elements. View factors for longwave and shortwave diffuse radiation exchange are computed once at the start of the simulation using a Monte Carlo ray tracing approach; for subsequent model timesteps, matrix inversion rapidly solves infinite reflections and interception of emitted longwave between all elements. The model is designed to simulate any combination of shortwave and longwave radiation frequency bands, and to be portable to any neighbourhood-scale urban canopy geometry based on the urban canyon. Additionally, the model is sufficiently flexible to represent forest and forest-clearing scenarios. Model sensitivity tests demonstrate the model is robust and computationally feasible, and highlight the importance of vertical resolution to the performance of urban canopy radiation models. Full model evaluation is limited by the paucity of within-canyon radiation measurements in urban neighbourhoods with trees. Where appropriate model components are tested against analytic relations and results from an independent urban radiation transfer model. Furthermore, system response tests demonstrate the ability of the model to realistically distribute shortwave radiation among urban elements as a function of built form, solar angle and tree foliage height, density and clumping. Separate modelling of photosynthetically-active and near-infrared shortwave bands is shown to be important in some cases. Increased canyon height-to-width ratio and/or tree cover diminishes the net longwave radiation loss of individual canyon elements (e.g., floor, walls), but, notably, has little effect on the net longwave loss of the whole urban canopy. When combined with parametrizations for the impacts of trees on airflow and hydrological processes in the urban surface layer, the new radiation model extends the applicability of urban canopy models and permits more robust assessment of trees as tools to manage urban climate, air quality, human comfort and building energy loads.     

RegCM4对中国东部区域气候模拟的辐射收支分析

利用卫星和再分析数据,评估了区域气候模式Reg CM4对中国东部地区辐射收支的基本模拟能力,重点关注地表净短波(SNS)、地表净长波(SNL)、大气顶净短波(TNS)、大气顶净长波(TNL)4个辐射分量。结果表明:1)短波辐射的误差值在夏季较大,而长波辐射的误差值在冬季较大。但各辐射分量模拟误差的空间分布在冬、夏季都有较好的一致性。2)对于地表辐射通量,SNS表现为正偏差(向下净短波偏多),在各分量中误差最大,区域平均误差值近50 W/m2;SNL表现为负偏差(向上净长波偏多);对于大气顶辐射通量,TNS和TNL分别表现为"北负南正"的误差分布和整体正偏差。3)利用空间相关和散点线性回归方法对4个辐射分量的模拟误差进行归因分析,发现在云量、地表反照率、地表温度三个直接影响因子中,云量模拟误差的贡献最大,中国东部地区云量模拟显著偏少。     

1984—2017年ISCCP-FH辐射资料在青藏高原地区的适用性评估

长序列卫星辐射资料的缺乏一直是制约青藏高原(以下简称高原)辐射长期变化研究的重要原因之一.对国际上最新提供的1984—2017年ISCCP-FH(以下简称FH)长序列卫星辐射资料中的大气顶逸出长波辐射(OLR)、到达地面短波辐射(SWD)、地面向上长波辐射(LWU)、到达地面长波辐射(LWD)进行分析,评估了FH辐射资...     

Warm winds from the Pacific caused extensive Arctic sea-ice melt in summer 2007

During summer 2007 the Arctic sea-ice shrank to the lowest extent ever observed. The role of the atmospheric energy transport in this extreme melt event is explored using the state-of-the-art ERA-Interim reanalysis data. We find that in summer 2007 there was an anomalous atmospheric flow of warm and humid air into the region that suffered severe melt. This anomaly was larger than during any other year in the data (1989?C2008). Convergence of the atmospheric energy transport over this area led to positive anomalies of the downward longwave radiation and turbulent fluxes. In the region that experienced unusual ice melt, the net anomaly of the surface fluxes provided enough extra energy to melt roughly one meter of ice during the melting season. When the ocean successively became ice-free, the surface-albedo decreased causing additional absorption of shortwave radiation, despite the fact that the downwelling solar radiation was smaller than average. We argue that the positive anomalies of net downward longwave radiation and turbulent fluxes played a key role in initiating the 2007 extreme ice melt, whereas the shortwave-radiation changes acted as an amplifying feedback mechanism in response to the melt.