Effects of Doubled Carbon Dioxide on Rainfall Responses to Radiative Processes of Water Clouds

The effects of doubled carbon dioxide on rainfall responses to radiative processes of water clouds are investigated in this study.Two groups of two-dimensional cloud-resolving model sensitivity experiments with regard to pre-summer heavy rainfall around the summer solstice and tropical rainfall around the winter solstice are conducted and their five-day averages over the model domain are analyzed.In the presence of radiative effects of ice clouds,doubled carbon dioxide changes pre-summer rainfall from the decrease associated with the enhanced atmospheric cooling to the increase associated with the enhanced infrared cooling as a result of the exclusion of radiative effects of water clouds.Doubled carbon dioxide leads to the reduction in tropical rainfall,caused by the removal of radiative effects of water clouds through the suppressed infrared cooling.In the absence of radiative effects of ice clouds,doubled carbon dioxide changes pre-summer rainfall from the increase associated with the strengthened atmospheric warming to the decrease associated with the weakened release of latent heat caused by the elimination of radiative effects of water clouds.The exclusion of radiative effects of water clouds increases tropical rainfall through the strengthened infrared cooling,which is insensitive to the change in carbon dioxide.     

RADIATIVE AND MICROPHYSICAL EFFECTS OF ICE CLOUDS ON A TORRENTIAL RAINFALL EVENT OVER HUNAN, CHINA

The radiative and microphysical effects of ice clouds on a torrential rainfall event over Hunan,China in June 2004 are investigated by analyzing the sensitivity of cloud-resolving model simulations.The model is initialized by zonally-uniform vertical velocity,zonal wind,horizontal temperature and vapor advection from National Centers for Environmental Prediction(NCEP) /National Center for Atmospheric Research(NCAR) reanalysis data.The exclusion of radiative effects of ice clouds increases model domain mean surface rain rates through the increase in the mean net condensation associated with the increase in the mean radiative cooling during the onset phase and the increases in the mean net condensation and the mean hydrometeor loss during the mature phase.The decrease in the mean rain rate corresponds to the decreased mean net condensation and associated mean latent heat release as the enhanced mean radiative cooling by the removal of radiative effects of ice clouds cools the mean local atmosphere during the decay phase.The removal of microphysical effects of ice clouds decreases the mean rain rates through the decrease in the mean net condensation during the onset phase,while the evolution of mean net condensation and the mean hydrometeor changes from decrease to increase during the mature phase.The reduction in the mean rain rate is primarily associated with the mean hydrometeor change in the absence of microphysical effects of ice clouds during the decay phase.     

Effects of doubled carbon dioxide on rainfall responses to large-scale forcing: A two-dimensional cloud-resolving modeling study

ABSTRACT Rainfall responses to doubled atmospheric carbon dioxide concentration were investigated through the analysis of two pairs of two-dimensional cloud-resolving model sensitivity experiments. One pair of experiments simulated pre-summer heavy rainfall over southern China around the summer solstice, whereas the other pair of experiments simulated tropical rainfall around the winter solstice. The analysis of the time and model domain mean heat budget revealed that the enhanced local atmospheric warming was associated with doubled carbon dioxide through the weakened infrared radiative cooling during the summer solstice. The weakened mean pre-summer rainfall corresponded to the weakened mean infrared radiative cooling. Doubled carbon dioxide increased the mean tropical atmospheric warming via the enhanced mean latent heat in correspondence with the strengthened mean infrared radiative cooling during the winter solstice. The enhanced mean tropical rainfall was associated with the increased mean latent heat.     

Radiative Forcing and Climate Response Due to Black Carbon in Snow and Ice

The radiative forcing and climate response due to black carbon(BC) in snow and/or ice were investigated by integrating observed effects of BC on snow/ice albedo into an atmospheric general circulation model(BCC AGCM2.0.1) developed by the National Climate Center(NCC) of the China Meteorological Administration(CMA).The results show that the global annual mean surface radiative forcing due to BC in snow/ice is +0.042 W m 2,with maximum forcing found over the Tibetan Plateau and regional mean forcing exceeding +2.8 W m 2.The global annual mean surface temperature increased 0.071 C due to BC in snow/ice.Positive surface radiative forcing was clearly shown in winter and spring and increased the surface temperature of snow/ice in the Northern Hemisphere.The surface temperatures of snow-covered areas of Eurasia and North America in winter(spring) increased by 0.83 C(0.6 C) and 0.83 C(0.46 C),respectively.Snowmelt rates also increased greatly,leading to earlier snowmelt and peak runoff times.With the rise of surface temperatures in the Arctic,more water vapor could be released into the atmosphere,allowing easier cloud formation,which could lead to higher thermal emittance in the Arctic.However,the total cloud forcing could decrease due to increasing cloud cover,which will offset some of the positive feedback mechanism of the clouds.     

Effects of Vertical Wind Shear on the Pre-Summer Heavy Rainfall Budget:A Cloud-Resolving Modeling Study

This study investigates the effects of vertical wind shear on the torrential rainfall response to the large-scale forcing using a rainfall separation analysis of a pair of two-dimensional cloud-resolving model sensitivity experiments for a pre-summer heavy rainfall event over southern China from 3-8 June 2008 coupled with National Centers for Environmental Prediction(NCEP)/Global Data Assimilation System(GDAS) data.The rainfall partitioning analysis based on the surface rainfall budget indicates that the exclusion of vertical wind shear decreases the contribution to total rainfall from the largest contributor,which is the rainfall associated with local atmospheric drying,water vapor divergence,and hydrometeor loss/convergence,through the reduction of the rainfall area and reduced rainfall during the rainfall event.The removal of vertical wind shear increases the contribution to total rainfall from the rainfall associated with local atmospheric drying,water vapor convergence,and hydrometeor loss/convergence through the expansion of the rainfall area and enhanced rainfall.The elimination of vertical wind shear enhances heavy rainfall and expands its area,whereas it reduces moderate rainfall and its area.     

黑碳气溶胶直接辐射强迫及其对中国夏季降水影响的模拟研究

利用NCAR的全球大气模式CAM3分析了黑碳气溶胶在大气顶和地表的直接辐射强迫分布及其季节变化,重点讨论了云对黑碳气溶胶直接辐射强迫的影响,以及黑碳气溶胶对中国夏季降水的影响。结果表明：黑碳气溶胶在大气顶和地表的直接辐射强迫分布范围和强度都具有明显的季节变化。有云条件下,黑碳气溶胶在大气顶产生正的直接辐射强迫,全球年平均强迫值为＋0.33 W·m－2;在地表产生负的直接辐射强迫,全球年平均强迫值为－0.56 W·m－2。晴空条件下,黑碳气溶胶在大气顶和地表的全球年平均辐射强迫值分别为＋0.21 和－0.71 W·m－2。云的存在对黑碳气溶胶的辐射强迫产生了很大的影响,使大气顶的正辐射强迫增加,地表的负辐射强迫减小。黑碳气溶胶导致夏季中国北方30°N～45°N之间区域降水明显增加;而中国长江以南地区除了海南和广西的部分城市外,降水明显减少。模拟结果表明,中国夏季近50年来经常发生的南涝北旱并非由黑碳气溶胶引起。     

南京北郊黑碳气溶胶的浓度观测及辐射强迫研究

利用2008年南京大学浦口校区气溶胶采样数据对碳气溶胶的浓度变化特征进行了分析,建立了由气溶胶光学参量计算模块(OPAC)和辐射传输模型(TUV)组成的箱模式,并结合实际观测资料,利用该模式对南京北郊黑碳气溶胶的光学厚度及辐射强迫进行了评估。结果表明:南京北郊黑碳气溶胶(BC)的年平均浓度为6.7±4.6μg/m3,有机碳气溶胶(OC)的年平均浓度为21.3±13.3μg/m3,有机碳与黑碳气溶胶浓度的平均比值为3.4。黒碳气溶胶浓度具有夏季低、冬春季高的特点。由箱模式计算得到的黒碳气溶胶的年均光学厚度为0.07,年均吸收系数为44 Mm–1。白天正午晴空条件下黑碳所造成的最大瞬时地面辐射强迫可达-22.9±14.3 W/m2,在大气层顶造成的最大瞬时辐射强迫为12.5±7.3 W/m2。     

辐射参数化方案对一个海气耦合模式云和辐射模拟的影响

比较Morcrette辐射方案和Fu_Liou辐射方案对NCC/IAP T63海气耦合模式云和辐射模拟的影响, 结果表明:两种方案模拟的大气顶入射辐射存在明显的差异; 晴空大气Fu_Liou方案的短波吸收能力在全球普遍较Morcrette方案低; 在60°S~60°N之间, Fu_Liou方案模拟的行星反照率更接近于ERBE卫星观测; 在对大气顶净辐射的模拟上, 除了冬季的太平洋和大西洋东岸云量明显减少的部分地区外, Fu_Liou方案对大气顶净辐射的模拟总体上较Morcrette方案有了较为明显的改善; Fu_Liou方案模拟的海洋低层云显著减少, 而热带地区高云的模拟明显增加; 由于采用了“二元云量”算法, 尽管云量有所减少, Fu_Liou方案模拟的云短波吸收作用仍有所增强, 一定程度上改进了Morcrette方案云的短波吸收作用偏弱的现象。     

Microphysical and radiative effects of ice clouds on diurnal variations of tropical convective and stratiform rainfall

Microphysical and radiative effects of ice clouds on diurnal variations of tropical convective and stratiform rainfall are examined with the equilibrium simulation data from three experiments conducted with a two-dimensional cloud resolving model with imposed temporally and zonally invariant winds and sea surface temperature and zero mean vertical velocity. The experiment without ice radiative effects is compared with the control experiment with ice microphysics (both the ice radiative and microphysical effects) to study effects of ice radiative effects on diurnal rainfall variations whereas it is compared with the experiment without ice microphysics to examine ice microphysical effects on the diurnal rainfall variations. The ice radiative processes mainly affect diurnal cycle of convective rainfall whereas the ice microphysical processes have important impacts on the diurnal cycles of both convective and stratiform rainfall. Turning off the ice radiative effects generally enhances convective rainfall during the morning and evening and suppresses convective rainfall in the afternoon whereas turning off the ice microphysical effects generally suppresses convective and stratiform rainfall during the morning and enhances convective and stratiform rainfall in the afternoon and evening. The ice radiative and microphysical effects on the diurnal cycle of surface rainfall are mainly associated with that of vapor condensation and deposition, which is controlled by air temperature through saturation specific humidity. The ice effects on the diurnal cycle of local temperature tendency are largely explained by that of latent heating since the diurnal cycle of radiation is insensitive to the ice effects.     

Responses of Vertical Structures in Convective and Stratiform Regions to Large-Scale Forcing during the Landfall of Severe Tropical Storm Bilis （2006）

The responses of vertical structures,in convective and stratiform regions,to the large-scale forcing during the landfall of tropical storm Bilis(2006) are investigated using the data from a two-dimensional cloud-resolving model simulation.An imposed large-scale forcing with upward motion in the mid and upper troposphere and downward motion in the lower troposphere on 15 July suppresses convective clouds,which leads to ～100% coverage of raining stratiform clouds over the entire model domain.The imposed forci...     

四川盆地西部暴雨对初始水汽条件敏感性的模拟研究

基于区域暴雨数值预报模式AREM, 针对2003年8月发生在四川盆地西部的多次局地强暴雨过程, 通过数值试验, 讨论了川西暴雨对初始水汽条件的高度敏感性, 揭示了川西暴雨过程独特的局地水汽循环特征。初始水汽条件不仅决定着暴雨的强度, 还对最大降水发生时间产生明显影响, 从而决定模式对降水日变化的模拟效果。局地初始水汽偏大, 不仅导致24小时降水总量的迅速增加, 甚至空报暴雨, 还使得主要降水时段明显提前, 使夜雨变为昼雨。局地初始水汽减少不仅会显著减小降水量, 甚至会致使暴雨消失,还会使主要降水时段滞后。     

Effects of Irrigation on Nitrous Oxide, Methane and Carbon Dioxide Fluxes in an Inner Mongolian Steppe

Increased precipitation during the vegetation periods was observed in and further predicted for Inner Mongolia. The changes in the associated soil moisture may affect the biosphere-atmosphere exchange of greenhouse gases. Therefore, we set up an irrigation experiment with one watered （W） and one unwatered plot （UW） at a winter-grazed Leymus chinensis-steppe site in the Xilin River catchment, Inner Mongolia. UW only received the natural precipitation of 2005 （129 mm）, whereas W was additionally watered after the precipitation data of 1998 （in total 427 mm）. In the 3-hour resolution, we determined nitrous oxide （N20）, methane （CH4） and carbon dioxide （CO2） fluxes at both plots between May and September 2005, using a fully automated, chamber-based measuring system. N20 fluxes in the steppe were very low, with mean emissions （±s.e.） of 0.9-4-0.5 and 0.7-4-0.5 μg N m^-2 h^-1 at W and UW, respectively. The steppe soil always served as a CH4 sink, with mean fluxes of -24.1-4-3.9 and -31.1-4- 5.3 μg C m^-2 h^-1 at W and UW. Nighttime mean CO2 emissions were 82.6±8.7 and 26.3±1.7 mg C m^-2 h^-1 at W and UW, respectively, coinciding with an almost doubled aboveground plant biomass at W. Our results indicate that the ecosystem CO2 respiration responded sensitively to increased water input during the vegetation period, whereas the effects on CH4 and N2O fluxes were weak, most likely due to the high evapotranspiration and the lack of substrate for N2O producing processes. Based on our results, we hypothesize that with the gradual increase of summertime precipitation in Inner Mongolia, ecosystem CO2 respiration will be enhanced and CH4 uptake by the steppe soils will be lightly inhibited.     

基于CCSM4.0长期积分试验评估不同辐射强迫对中国干旱半干旱区降水的影响

本文基于气候系统模式CESM4.0长期积分试验,分析评估了工业革命前（1850年）及当前（2000年）两种辐射强迫作用（分别为太阳活动和温室气体）对中国北方干旱半干旱区降水的影响。结果表明,模拟结果与观测之间尽管存在一定的偏差,但仍能再现降水气候态的空间分布以及季节变化特征;两种辐射强迫下的降水长期变化均无明显趋势,但二者的差异却呈现出70~100年的准周期振荡;由人类活动引起的当前辐射强迫作用对降水的多年际变率幅度有一定影响,造成极端强降水事件出现的概率增多,而由太阳活动引起的辐射强迫作用主要对降水多年代际周期具有一定的调制作用。进一步分析表明,两种辐射强迫下中国北方干旱半干旱区降水年多年代际变率的主要模态基本一致,但人类活动引起的辐射强迫作用会影响降水多年代际变率与热带海温异常的相互作用的强度,从而改变降水多年代际变率的幅度。     

实施低碳水泥标准的影响及协同减排效果分析

采用MAP-CGE模型,模拟了我国水泥行业实施低碳水泥标准对不同生产工艺产出、能耗及污染排放的影响,测算了对其边际减排成本和均衡价格的影响,分析了对不同污染物的协同减排效果。模拟结果表明：实施低碳水泥标准有利于水泥生产工艺的升级换代,并有助于水泥行业节能减排;在现有技术水平下,水泥行业在减排1 t CO2的同时将带来约1.17 kg的SO2减排量和4.44 kg的NOx减排量;实施低碳水泥标准对于水泥行业控制NOx排放很有利;但水泥行业也需承担减排成本并导致其均衡价格的小幅上升。     

土壤水分条件对内蒙古典型草原水汽和二氧化碳通量的影响研究

本文基于2007年和2008年生长季内蒙古羊草和大针茅草原湍流观测资料,分析了两种典型草原下垫面生长季的不同土壤水分条件下水汽和二氧化碳通量交换特征及其控制因子。主要结果如下:（1）在植被生长峰值期,日尺度上,干旱条件下土壤湿度是潜热通量的主要控制因子,而土壤水分条件较好时潜热通量主要受净辐射控制。（2）与大针茅草原相比,羊草草原叶面积指数较大,水分条件较好时,其潜热通量平均值更大,CO₂吸收能力更强,吸收CO₂更多;但在土壤水分胁迫出现时,羊草草原叶面的气孔闭合度急剧增加,大针茅草原的潜热通量、和CO₂吸收反而更大,表现出更为耐旱的植被特性。（3）地表导度可以用来解释土壤水分条件对羊草和大针茅草原碳水通量的影响。     

热带印度洋-西太平洋水汽输送异常对中国东部夏季降水的影响

利用1979~2015年NCEP/NCAR发布的月平均全球再分析资料,分析了热带印度洋-西太平洋水汽输送异常对中国东部夏季降水的影响及其形成机理。研究结果表明:热带印度洋-西太平洋地区（10°S~30°N,60°~140°E）夏季异常水汽输送主要包括两个模态,他们可以解释总的水汽输送异常34%的方差。其中,第一模态（EOF1）表现为异常水汽沿反气旋从热带西太平洋经过南海及孟加拉湾输送到中国东部上空,对应南海、孟加拉湾水汽路径输送均偏多,此时西太平洋副热带高压显著偏强,异常水汽在长江中下游地区辐合并伴随显著上升运动,有利于长江中下游降水偏多;第二模态（EOF2）表现为异常水汽从热带印度洋沿阿拉伯海、印度半岛、中南半岛等呈反气旋式输送,华南上空相应出现气旋式水汽输送异常,并对应异常水汽辐合和上升运动,有利于华南降水偏多。就可能的外部成因而言,EOF1与ENSO关系密切,表现为前冬热带中东太平洋显著偏暖,夏季同期热带北印度洋、南海上空显著偏暖,造成西太平洋副热带高压显著偏强,异常水汽主要来源于热带西太平洋和南海;EOF2与同期热带印度洋偶极子（TIOD）异常有关,TIOD为正位相时热带印度洋上空出现异常东风,华南上空出现异常气旋并伴随水汽异常辐合,异常水汽主要来源于热带南印度洋。     

气候与植被覆盖变化对中国西南亚高山区流域碳水循环的影响模拟

正确认识气候变化对流域森林植被和水文的影响对于林业经营管理与流域生态修复具有重要意义。为了揭示气候与植被覆盖变化对西南亚高山区流域碳水循环过程的影响,用生物物理/动态植被模型SSiB4/TRIFFID（Simplified Simple Biosphere model version 4, coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics model）与流域地形指数水文模型TOPMODEL（Topographic Index Model）的耦合模型（以下记为SSiB4T/TRIFFID）模拟了不同气候情景下西南亚高山区的梭磨河流域植被演替和碳水循环过程。结果表明,所有试验流域植被经历了从C3到苔原灌木最后到森林的变化;控制试验流域蒸散在流域植被主要为苔原灌木时达到最大而径流深最小;增温5 ℃并且增雨40%试验[记为T+5, (1+40%) P试验]流域蒸散在流域为森林覆盖时达到最大而径流深最小。随着温度增加,森林蒸腾、冠层截留蒸发和蒸散的增加幅度明显大于草和苔原灌木,导致森林从控制试验的增加径流量变为减小径流量。从控制试验到T+5, (1+40%) P试验,温度增加使森林净初级生产力有所增加,但对草和苔原灌木的净初级生产力影响很小;植被水分利用效率随温度增加明显减小。西南山区随着海拔高度降低（温度升高）,森林从增加径流量转变为减少径流量,植被水分利用效率也相应明显减小。西南山区气候的垂直地带性对森林—径流关系和水分利用效率的空间变化有着重要的影响。