辐射传输模式中地表参数对大气长波辐射的影响

本文利用Liou-Ou一维宽带辐射传输模式，对地表热力参数取值部分作了改进，使用模式大气和青藏高原实测资料对下垫面温度与地表空气温度两者不能合二为一的问题进行了分析，同时还讨论了下垫面温度的日变化对大气长波辐射通量日变化的影响及地表比辐射率的变化对大气长波辐射通量计算结果的修正作用。     

从FY-4A卫星遥感数据和GFS资料估算全天空状况下的地表长波辐射通量

本文介绍一种利用FY-4A成像仪遥感数据和全球预报系统(GFS)资料估算全天空地表长波辐射通量的反演方法。该方法通过辐射传输模拟和统计回归计算建立云天地表下行长波辐射通量的反演模式,并基于GFS资料处理云覆盖地区的地表上、下行长波辐射通量。这种全天空状况下两种通量的反演结合了FY-4A晴空地表长波辐射业务产品和本文反演模式处理的云天地表上、下行长波辐射通量。2018年9月1日的处理结果与Aqua/CERES同类产品相对比,精度为:RMSE=20.52 W·m^-2,R=0.9481,Bias=3.3 W·m^-2(夜间地表下行辐射通量对比);RMSE=25.58 W·m^-2,R=0.9096,Bias=5.4 W·m^-2(白天地表下行辐射通量对比);RMSE=10.97 W·m^-2,R=0.9762,Bias=-3.3 W·m^-2(夜间地表上行辐射通量对比);RMSE=19.97 W·m^-2,R=0.9283,Bias=5.0 W·m^-2(白天地表上行辐射通量对比)。这些结果表明本文发展的方法能够反演出精度较好的云天上下行长波辐射通量资料,为今后利用FY-4后续星处理生成全天空状况下的地表长波辐射通量产品奠定了理论基础。     

FY 2D静止气象卫星OLR反演模式

介绍FY2D卫星OLR反演模式的建立过程以及模式与NOAA卫星OLR反演模式的相互对比,包括：地球大气红外辐射传输方程,全球3812条大气廓线的大气顶射出辐射率、射出长波辐射通量密度的模拟计算,3812条廓线FY2D窗区通道1、2、水汽通道的通道辐射率模拟计算, 通道辐射率的临边变暗订正关系式的确立、3个通道波段的窄波段辐射通量密度的模拟计算。通过3812条廓线的窄波段辐射通量密度与OLR的XY坐标散点图,建立OLR回归关系式;并通过NOAA17 AVHRR通道5 OLR反演模式与FY2D窗     

一次沙尘天气过程中沙尘气溶胶对辐射的影响

沙尘气溶胶对辐射有显著影响,利用耦合了Shao2004起沙参数化方案的WRF/Chem(大气/化学全耦合模式),模拟分析了沙尘天气过程中沙尘气溶胶对辐射的影响。结果发现沙尘气溶胶可以导致地面向下的短波辐射通量减小42.51%,平均减小-3.30~-49.46 W·m~(-2),最大可达-162.67 W·m~(-2);沙尘气溶胶可以通过自身向外发射长波辐射,导致地面向下的长波辐射通量增大,地面向下的长波辐射通量平均增加为17.49~50.49 W·m~(-2),最大可达99.17 W·m~(-2)。当PM10浓度为10~20 mg·m-3,沙尘气溶胶能够减小地面向下的长波辐射通量,即沙尘气溶胶在该地区对大气具有"保温"作用;白天沙尘气溶胶主要增加大气层顶向上的长波辐射通量,夜间则减少大气层顶向上的长波辐射通量,大气层顶向外的长波辐射通量平均变化为-25.29~28.83 W·m~(-2),最大可达87.22 W·m~(-2)。     

海雾的准周期振荡特征

根据南海北部海雾外场观测获取的高分辨率液态含水量、长波辐射通量数据,采用小波分析方法分析了2008年3月16—17日和18—19日两次海雾中的液态水含量、净长波辐射通量的变化特征,讨论南海北部海雾发展和维持的冷却机制。结果显示:(1)无论在有云或无云条件下,海雾都可发展和维持;但前者的液态含水量明显小于后者,而风速大于后者;(2)在地面海雾的生成之前和生成初期,净辐射通量都存在准周期振荡现象,无论无云/有云,地面海雾液态水的大幅度发展的阶段都存在含水量的准周期振荡现象;(3)含水量的准周期振荡现象与振荡发生时段的长波辐射通量关系不大,而主要通过湍流对液态水的混合作用与高空海雾液态水大量生成阶段的雾顶长波辐射间接相关。(4)海雾的生成都与雾顶长波辐射冷却密切相关,但发展和维持可通过不同的冷却机制,既可通过海气间湍流热量输送和辐射传输,也可通过雾顶长波辐射冷却。     

气候模式中云的次网格结构对全球辐射影响的研究

利用一种用于大尺度天气、气候模式的随机云产生器(SCG)和独立气柱近似(ICA)辐射算法,研究了次网格云的水平结构以及垂直重叠结构对全球辐射场的影响.比较了水平非均匀云(IHCLD)和水平均匀云(HCLD)的辐射场差异以及云的最大.随机重叠(MRO)和一般重叠(GenO)的辐射场差异.结果显示,与HCLD相比,IHCLD一方面可增加地面净短波辐射通量,纬向平均最大值(约1W/m~2)和次大值(约0.6 W/m~2)分别位于高纬度低云密集地区和对流旺盛的热带地区;另一方面可增加大气顶的净长波辐射通量,纬向平均最大值(0.3 W/m~2)出现在热带地区.不同的重叠结构对短波和长波辐射收支也有很大的影响.MRO和GenO的短波辐射通量差异在热带辐合带最大.达到30-40W/m~2,在高纬度低云带的纬向平均也可达到5W/m~2左右;长波辐射通量差异具有相似的地区分布,但量值相对较小.不同重叠结构可以造成大气上下层的辐射加热率差异,影响大气热力层结.云的水平和垂直结构对有云区域辐射收支的影响将改变大气热力、动力状况以及水汽条件,从而影响模拟的气候系统的演变.文中采用单向云-辐射计算,排除了与气候系统其他过程复杂的相互作用,从而使其结果具有一定的普适性,可为不同大尺度模式进行次网格云辐射参数化提供参考.     

青海湖北岸大气向下长波辐射特征及云的影响

大气向下长波辐射对地表能量平衡、水循环等有重要影响。基于青海湖北岸2018年9月至2019年8月辐射观测资料,分析不同时间尺度的辐射通量变化特征,对比晴天条件下10个大气比辐射率参数化公式在该地区的适用性,在此基础上定量评估了云对大气向下长波辐射的影响。结果显示:青海湖北岸地区各辐射分量均呈现相似的"单峰型"日变化特征,辐射量白天较高、夜间较低;一年中,除向上短波辐射(主要受地表反照率影响)外,其余辐射分量均随气温而变化。晴天条件下大气比辐射率参数化Brutsaert公式在青海湖北岸地区的适用性最高。随着云份额数(C_f)的增大,青海湖北岸大气向下长波辐射逐渐增强,在C_f10%时,云增强效应低于10 W·m~(-2);当C_f75%时,云增强效应超过60 W·m~(-2)。云天大气向下长波辐射观测值与晴天计算值的比值r随着C_f的增大而增大,两者存在极显著的二次函数关系,当C_f10%时,r平均为1.04;当C_f75%时,r1.25,该统计关系能够较好地揭示青海湖北岸地区云对大气向下长波辐射的影响。     

FY-2D静止气象卫星OLR反演模式

介绍FY-2D卫星OLR反演模式的建立过程以及模式与NOAA卫星OLR反演模式的相互对比,包括:地球大气红外辐射传输方程,全球3812条大气廓线的大气顶射出辐射率、射出长波辐射通量密度的模拟计算,3812条廓线FY-2D窗区通道1、2、水汽通道的通道辐射率模拟计算,通道辐射率的临边变暗订正关系式的确立、3个通道波段的窄波段辐射通量密度的模拟计算.通过3812条廓线的窄波段辐射通量密度与OLR的X-Y坐标散点图,建立OLR回归关系式;并通过NOAA-17 AVHRR通道5 OLR反演模式与FY-2D窗区通道2 OLR反演模式形式的互比,得出两星的OLR反演模式接近,给出2007年2～4月OLR产品个例和产品精度分析.     

2008年夏季风期间西沙海域海-气通量交换及热量收支

2008年4—10月在中国南海西沙永兴岛近海进行了第4次海-气通量观测试验,获得了整个夏季风期间近海面层湍流脉动量及辐射、表层水温、波浪及距水面3.5、7.0、10.5m高度温、湿、风梯度观测资料,根据涡动相关法和COARE3.0法计算结果研究了2008年南海西南季风爆发、发展、中断、衰退包括暴雨、台风、冷空气影响等天气过程中海-气通量交换和热量收支变化。结果表明:(1)季风爆发前的晴天太阳总辐射强,而海洋失热量较小,热量净收支为较大正值,海面温度迅速升高。季风爆发期太阳总辐射仍然较强,大气长波辐射也有所增强,而海面长波辐射变化很小,故海面净辐射收支仍为正值;(2)季风活跃期特别是降水阶段感热通量增大,季风中断阶段变小;季风活跃期虽然潜热通量增大,由于太阳短波辐射没有减少,海洋净热量收支稍有盈余;中断阶段潜热通量、感热通量减少,海洋吸热大于季风活跃期;降水阶段由于太阳短波辐射减小,感热通量增大,海洋热量收支出现较大负值,海面温度很快降低。季风衰退期风力减弱,湿度减小,潜热通量减小,海洋热量收入又出现较大正值,海面温度回升;(3)台风影响过程中潜热通量随着风速增强迅速增大;感热通量因降水情况不同而有差异,晴天时减小,大雨时剧烈增大;由于太阳短波辐射减少、潜热通量剧增,海洋热量净收支出现负值,促使海面温度迅速降低;(4)动量通量主要与海表面风速有关;动量通量τ与风速V的关系可以表示为τ=0.00171v~2-0.003809v+0.02213。     

青藏高原东部多、少雪年地表能量和水分特征对比研究

青藏高原积雪对地表能量和水分交换有重要影响。本文通过选取青藏高原东部玛多、玛曲和垭口3个站点多雪年和少雪年的气象资料,对比分析了多雪年和少雪年的地表能量和土壤水热特征。结果表明：在地表辐射平衡方面,多雪年或积雪较多的时期可以反射掉较多的向上短波辐射。玛多站多雪年反射掉的向上短波辐射是少雪年的2.3倍,玛曲站主要积雪期（3-5月）中多雪时期比少雪时期多反射掉10.07 W·m^-2的向上短波辐射,垭口站多雪年的年平均向上短波辐射分别比两个少雪年高出37.49 W·m^-2和31.92 W·m^-2。多雪年或积雪较多的时期还可以减少向上长波辐射的发射。玛多站多雪年与少雪年向上长波辐射的差值在整个研究时段中基本为负,垭口站两个少雪年在当年12月初到次年1月和次年2月末到4月初这两个时段,积雪越深,向上长波辐射值越小。向上短波和向上长波辐射的差异使得多雪年的地表净辐射少于少雪年。不论多雪年还是少雪年,土壤热通量的值都很小,地表能量分配主要以感热通量和潜热通量为主。玛多站少雪年以感热通量为主且感热通量为正,但多雪年感热通量为负;玛曲站的...     

Calculating downward longwave radiation under clear and cloudy conditions over a tropical lowland forest site: an evaluation of model schemes for hourly data

Field measurements of radiation fluxes—notably downwelling longwave radiation flux (LW flux)—are as yet rare or nonexistent outside a very select number of sites in the tropics. Data gaps can only be filled through the use of estimation schemes based on measurements of other meteorological variables, and there is a need for recommendations on best practice in this area. We selected 18 contrasting semi-empirical estimation schemes for downward longwave radiation, based on air emissivities, combined with six different sky cover estimation schemes and compared the expected longwave flux with hourly observations from a flux tower at Caxiuan? in Brazil. Of all schemes tested, the Dilley–Kimball emissivity scheme combined with Kasten and Czeplak’s sky cover scheme during the day and Dilley and O’Brien’s model B scheme at night proved to be the most reliable, yielding estimates of LW flux generally within 20?W/m² of measurements across all time points.     

长波区间太阳辐射对气候模拟的影响

长波区间的太阳辐射在气候模式中往往被忽略。利用国家气候中心BCC_AGCM2.0.1大气环流模式,采用矩阵算子辐射传输算法,研究了长波区间太阳辐射对气候模式辐射通量和温度模拟结果的影响。结果表明,以ISCCP和CERES辐射资料为标准,考虑长波区间太阳辐射后,长波区间晴空大气地表向下辐射通量平均误差减小2.05 W/m2,均方根误差减少1.29 W/m2;长波区间晴空大气模式顶向上辐射通量平均误差减小0.70 W/m2,均方根误差减小0.21 W/m2;长波区间有云大气地表向下辐射通量平均误差减小1.38 W/m2,均方根误差减小1.03 W/m2;长波区间有云大气模式顶向上辐射通量平均误差减小0.99 W/m2,均方根误差减小0.30 W/m2。以ECMWF再分析资料为标准,考虑长波区间太阳辐射后,赤道地区上对流层—下平流层区域温度的冷偏差得到改善,对流层顶温度平均误差减小0.27 K,均方根误差减小0.25 K。     

Greenhouse effect and altitude gradients over the Alps – by surface longwave radiation measurements and model calculated LOR

Summary The greenhouse effect has been investigated predominantly with satellite measurements, but more than 90% of the greenhouse radiative flux affecting Earths surface temperature and humidity originates from a 1000 meter layer above the surface. Here we show that substantial improvements on surface longwave radiation measurements and very good agreement with radiative transfer model calculations allow the clear-sky greenhouse effect be determined with measured surface longwave radiation and calculated longwave outgoing radiation at the top of the atmosphere. The cloud radiative forcing is determined by measured net longwave fluxes and added to the clear-sky greenhouse effect to determine the all-sky greenhouse effect. Longwave radiation measurements at different altitudes were used to determine the clear-sky and all-sky annual and seasonal greenhouse effect and altitude gradients over the Alps. Linear altitude gradients are measured for clear-sky situations, whereas the all-sky greenhouse effect is strongly influenced by varying, cloud amounts at different altitudes. Large diurnal and seasonal variations show the importance of surface heating and cooling effects and demonstrate the strong coupling of the greenhouse effect to surface temperature and humidity.     

不同形状冰晶权重假定对冰云光学和辐射特性的影响

在BCC_RAD辐射传输模式和包含多形状冰晶粒子的冰云光学性质参数化方案的基础上,详细分析了不同冰晶粒子权重选取对冰云光学和辐射特性的影响。结果显示,不同形状冰晶粒子权重的选取对长波带平均消光系数、单次散射比、不对称因子和短波带平均不对称因子均有较大的影响。冰晶粒子权重选取对长波辐射通量有很大影响:对长波向下辐射通量,权重选择不同可在云底处造成高达10.50 W/m2的差别;对长波向上辐射通量,权重选择不同可在云顶处造成高达15.05 W/m2的差别。冰晶粒子权重选择对短波辐射通量也存在较大影响:对短波向下辐射通量,权重选择不同可在云底处造成高达12.48 W/m2的差别;对短波向上辐射通量,权重选择不同可在云顶处造成高达10.23 W/m2的差别。冰晶粒子权重选择对长波加热率影响较大,在云顶处和云底处分别可达1.31和-2.06 K/d。研究表明,不同形状冰晶粒子权重的选取对冰云光学性质和辐射计算均有较大的影响,在长波区间尤其明显。      

热带太平洋和印度洋热源对大气影响的季节变化特征

本文利用1970—1979年COADS2°×2°格点月平均资料,计算了30°S—30°N热带太平洋和印度洋洋面上的有效长波辐射、感热和潜热通量以及它们的季节变化和年变化。结果指出:在冬季半球热带海洋外侧有大量的长波辐射、感热和潜热向大气输送,输送通量的季节变化大;热带太平洋地区西北部热通量的季节变化最大,赤道洋面地区热通量的年变化最小,潜热是洋面上热量输送的最大项,季节变化也最大;感热的输送量虽不及有效长波辐射,但其季节变化与有效长波辐射的变化相当;赤道地区是有效长波辐射和潜热通量的低值区,暖池地区是有效长波辐射的低值中心,靠近秘鲁海域的东南赤道太平洋是感热通量的负值区;热带太平洋西北部和阿拉伯海、孟加拉湾地区的热通量及年、季变化与亚洲季风有密切的关系,同时对我国和南亚地区的气候有重要的影响。      

Estimating Net Radiation from Air Temperature for Diffusion Modelling Applications in a Tropical Area

A simple and straightforward expression isproposed, which is based on the Fourier seriesdecomposition technique, for estimating hourly averagednet radiation from the corresponding values of airtemperature at a tropical location in West Africa. Thecomparisons made of the estimated net radiation withactual measurements (case studies) clearlydemonstrate that the scheme is efficient, both inclear and under cloudy weather conditions. Theestimates are also shown to be better than thosedetermined from an alternative relationship usingparametrizations for the shortwave and longwave components at the surface. The presentprocedure can easily be implemented in existingmeteorological preprocessors to calculate the sensibleheat flux for the Gaussian-based air pollutionmodels.     

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.     

Simulation of Non-Homogeneous CO_2 and Its Impact on Regional Temperature in East Asia

Carbon dioxide(CO_2) is an important greenhouse gas that influences regional climate through disturbing the earth's energy balance. The CO_2 concentrations are usually prescribed homogenously in most climate models and the spatiotemporal variations of CO_2 are neglected. To address this issue,a regional climate model(RegCM4) is modified to investigate the non-homogeneous distribution of CO_2 and its effects on regional longwave radiation flux and temperature in East Asia. One-year simulation is performed with prescribed surface CO_2 fluxes that include fossil fuel emission, biomass burning, air-sea exchange, and terrestrial biosphere flux. Two numerical experiments(one using constant prescribed CO_2 concentrations in the radiation scheme and the other using the simulated CO_2 concentrations that are spatially non-homogeneous) are conducted to assess the impact of non-homogeneous CO_2 on the regional longwave radiation flux and temperature. Comparison of CO_2 concentrations from the model with the observations from the GLOBALVIEW-CO_2 network suggests that the model can well capture the spatiotemporal patterns of CO_2 concentrations. Generally, high CO_2 mixing ratios appear in the heavily industrialized eastern China in cold seasons, which probably relates to intensive human activities. The accommodation of non-homogeneous CO_2 concentrations in the radiative transfer scheme leads to an annual mean change of -0.12 W m~(-2) in total sky surface upward longwave flux in East Asia. The experiment with non-homogeneous CO_2 tends to yield a warmer lower troposphere.Surface temperature exhibits a maximum difference in summertime, ranging from -4.18 K to 3.88 K, when compared to its homogeneous counterpart. Our results indicate that the spatial and temporal distributions of CO_2 have a considerable impact on regional longwave radiation flux and temperature, and should be taken into account in future climate modeling.     

A hybrid technique for computing the monthly mean net longwave surface radiation over oceanic areas

Summary Global maps of the monthly mean net upward longwave radiation flux at the ocean surface have been obtained for April, July, October 1985 and January 1986. These maps were produced by blending information obtained from a combination of general circulation model cloud radiative forcing fields, the top-of-the-atmosphere cloud radiative forcing from ERBE and TOVS profiles and sea surface temperature on ISCCP C1 tapes. The fields are compatible with known meteorological regimes of atmospheric water vapor content and cloudiness. There is a vast area of high net upward longwave radiation flux (> 80 W m^–2) in the eastern Pacific Ocean throughout most of the year. Areas of low net upward longwave radiation flux (< 40 Wm^–2) are the tropical convective regions and extra tropical regions that tend to have persistent low cloud cover. The technique used in this study relies on GCM simulations and so is subject to some of the uncertainties associated with the model. However, all input information regarding temperature, moisture and cloud cover is from satellite data having near global coverage. This feature of the procedure alone warrants its consideration for further use in compiling global maps of the net longwave radiation at the surface over the oceans.With 9 Figures