Global Climate Internal Variability in a 2000-year Control Simulation with Community Earth System Model(CESM)

Using the low-resolution(T31, equivalent to 3.75°× 3.75°) version of the Community Earth System Model(CESM) from the National Center for Atmospheric Research(NCAR), a global climate simulation was carried out with fixed external forcing factors(1850 Common Era.(C.E.) conditions) for the past 2000 years. Based on the simulated results, spatio-temporal structures of surface air temperature, precipitation and internal variability, such as the El Nio-Southern Oscillation(ENSO), the Atlantic Multi-decadal Oscillation(AMO), the Pacific Decadal Oscillation(PDO), and the North Atlantic Oscillation(NAO), were compared with reanalysis datasets to evaluate the model performance. The results are as follows: 1) CESM showed a good performance in the long-term simulation and no significant climate drift over the past 2000 years; 2) climatological patterns of global and regional climate changes simulated by the CESM were reasonable compared with the reanalysis datasets; and 3) the CESM simulated internal natural variability of the climate system performs very well. The model not only reproduced the periodicity of ENSO, AMO and PDO events but also the 3–8 years variability of the ENSO. The spatial distribution of the CESM-simulated NAO was also similar to the observed. However, because of weaker total irradiation and greenhouse gas concentration forcing in the simulation than the present, the model performances had some differences from the observations. Generally, the CESM showed a good performance in simulating the global climate and internal natural variability of the climate system. This paves the way for other forced climate simulations for the past 2000 years by using the CESM.

海气耦合模式CESM1中热带印度洋SST模拟偏差的来源分析

热带海表温度(SST)模拟偏差是困扰海气耦合模式发展的经典问题之一,其原因仍不完全清晰。针对海气耦合模式CESM1(Community Earth System Model version 1)模拟的热带印度洋SST偏差,我设计了单独大气-陆面模式、单独海洋-海冰模式以及海气耦合模式等一系列数值实验。在此基础上,采用大气-陆面模式和海洋-海冰模式隐式(implicit)SST偏差的分析方法,诊断了CESM1模拟的热带印度洋SST偏差的来源,并分析了大气模式和海洋模式中影响热带印度洋上层海温模拟的主要因素。通过分析热带印度洋不同地区SST的模拟偏差来源,发现耦合模式CESM1中孟加拉湾SST模拟偏冷主要是由海洋-海冰模式中过强的垂直混合、平流作用等海洋动力偏差引起的。在阿拉伯海和赤道西印度洋,过多的潜热释放导致SST降低,大气-陆面模式模拟误差是这两个海域SST冷偏差的主要来源。对于赤道中印度洋,潜热通量偏差和垂直混合、平流作用等模拟误差共同影响上层海水温度,潜热释放偏少、海水垂直混合偏弱以及经向平流向南输送过多暖水使耦合模式模拟的赤道中印度洋SST出现暖偏差,而在赤道东印度洋,模拟的SST偏冷是由大气-陆面模式中短波辐射偏少和海洋-海冰模式中海水垂直混合过强引起的,潜热通量偏差影响较小。分析表明,耦合模式中海气相互作用只影响SST模拟偏差的大小,但不是引起SST偏差的根本原因。

全球模式NCAR CESM和CAS ESM对亚洲东部夏季气候的模拟性能评估:气候平均态和降水日变化分析

主要评估了美国国家大气研究中心的NCAR CESM(Community Earth System Model,NCAR)和中国科学院的CAS ESM(Earth System Model,Chinese Academy of Sciences)两个地球系统模式对亚洲东部夏季气候态的模拟性能。使用NCAR CESM和CAS ESM各两种不同的水平分辨率,一共进行了4组长达19年(1998~2016年)的数值积分试验,并通过对2 m气温、降水强度和降水日变化等的分析,比较了这两个模式在亚洲东部的模拟性能。结果表明,CAS ESM和NCAR CESM均能模拟出夏季2 m气温和降水强度的大尺度分布特征,但整体上模拟得到的地表面气温偏暖、降水强度偏弱。对于降水日变化而言,观测的日降水峰值在陆地上主要发生在下午到傍晚时段,在海洋上则出现在午夜到凌晨时段。两组低分辨率试验模拟的陆地降水峰值出现过早,且无法模拟出四川盆地的夜间降水峰值和部分海洋地区凌晨或上午的降水峰值。提高分辨率对模式的模拟性能有显著的提升作用。高分辨率下,NCAR CESM和CAS ESM对陆地和海洋的降水日变化模拟性能都明显提高。对降水日变化的定量化分析表明,高分辨率CAS ESM模式对整个亚洲东部降水日变化的模拟最优。目前模式对海陆风的模拟还不太理想,未来要进一步提高模式模拟性能,需要重点完善与气温、降水过程相关的物理参数化方案。

CESM模式对东亚地区环流特征的模拟检验

利用CMAP逐月降水资料和欧洲天气预报中心ERA-interim的再分析资料,分析了CESM模式对东亚地区降水及夏季环流的模拟性能。结果表明:(1)CESM可以模拟出东亚地区大气环流、地表温度、水汽输送及降水随季节南北进退等主要特征。(2)该模式降水模拟结果与CMAP资料的对比显示,冬季降水的空间偏差主要表现为青藏高原南侧模拟降水偏多,而青藏高原西北部和日本海附近降水模拟偏少。夏季降水的空间偏差主要表现为陆地偏多,偏差最显著的区域位于青藏高原南侧,而海洋上偏少。降水偏差在季节变化上主要体现为低纬度地区雨带出现时间偏早,中高纬度地区出现时间偏晚且持续时间偏长。(3)模式模拟的夏季地表温度与ERA再分析资料相比在陆地模拟的结果明显偏低,在海洋上模拟的偏高。模式模拟的夏季500 h Pa西太副高较ERA再分析结果异常偏西至我国的江淮地区且强度偏强,这与模式模拟的夏季江淮地区降水较CMAP结果偏少密切相关。(4)夏季经向垂直环流的对比显示,模式模拟结果与ERA再分析结果的主要差异出现在青藏高原及其附近地区,模拟结果在高原的南北侧均出现明显的异常垂直环流,南侧的异常垂直环流伸展高度高,范围狭窄,这与模式模拟的夏季降水在高原南侧明显偏多有关。

基于国产众核架构CESM中有限差分计算优化

针对CESM中的有限差分算法并行过程中存在内存读取冗余过大、通信开销过高的问题,设计出根据数据结构进行数据重构、计算核心捆绑、流水线通信等多种并行优化方案。弥补了申威26010处理器在数据读取过程中缺少共享缓存区、带宽利用率不高等不足,缓解了申威26010处理器在有限差分法求解过程的通信瓶颈。对CESM中以有限差分法为核心计算的两个函数,在申威26010众核处理器上的测试结果表明,提出算法及优化策略拥有21.2倍的性能提升。

地表气温引入CESM模式对东亚地区夏季降水和环流场的影响

将地表气温分析场更新到CESM模式模拟场中,对比更新和未更新地表气温模拟得到的1980—2009年东亚地区夏季降水场和环流场各物理量的时空分布差异。结果表明,更新模式的地表气温、降水、水汽通量、纬向和经向环流场的模拟都得到明显改进,更新后的模拟场与再分析场的相关系数显著高于未更新的。

SST effect on the pre-monsoon intraseasonal oscillation over the South China Sea based on atmospheric-coupled GCM comparison

The role of sea surface temperature(SST)variability in the pre-monsoonal(April to July)intraseasonal oscillation(ISO)over the South China Sea(SCS)is investigated using the Community Earth System Model Version 2(CESM2).An Atmospheric Model Intercomparison Project(AMIP)simulation forced by daily sea surface temperatures(SSTs)derived from a parallel coupled general circulation model(CGCM)run was compared with observations and the mother coupled simulation.In the coupled model,the SST warming leads the peak convection about 1/4 period as in observations.The paralell uncoupled model fails to simulate this phase relationship,implying the importance of air-sea coupling in reproducing realistic ISO.Due to the near-quadrature phase relationship between SST and precipitation ISOs during the ISO events,it is difficult to distinguish the active/passive role of SST from observations alone.Significant correlation in intraseasonal precipitation between the daily SST-forced AMIP and mother CGCM runs indicates that SST plays a role in driving the atmospheric ISO.

基于耦合气候模式的始新世全球季风数值模拟

全球一半以上人口生活在季风区。为了研究温室气候时期全球季风气候的特征,利用耦合气候数值模式(Community Earth System Model),模拟了距今最近的温室气候时期——始新世(40 Ma B.P.)的全球季风气候特征。该模式全面考虑了大气、海洋、陆地、陆冰、海冰、植被等气候子系统的耦合作用,大气CO2含量设为工业革命前的4倍。模拟结果表明,在始新世时期,全球季风的范围、强度与现今大体相当,但是区域上,各季风区的特征与现今有明显差异。

臭氧卫星观测资料同化系统构建及其试验研究

为检验臭氧卫星资料同化对臭氧分析场和预报场的影响,基于集合平方根滤波(ENSRF)理论,结合通用地球系统模式(CESM),构建了CESM-ENSRF同化预报系统。系统构建过程考虑了卡尔曼滤波同化中的关键问题:利用全场随机扰动对初始场加扰,结合一般协方差膨胀和松弛协方差膨胀方法实现协方差膨胀,使用五阶距离相关函数进行协方差局地化。将构建的系统用于微波临边探测器(MLS)臭氧廓线数据的同化,分析臭氧卫星资料同化对模式预报的影响。结果表明:构建的CESM-ENSRF同化系统有效实现了臭氧资料同化,臭氧卫星资料同化对臭氧分析场和预报场精度有较大改进。

Evaluation of East Asian Summer Climate Prediction from the CESM Large-Ensemble Initialized Decadal Prediction Project

Based on surface air temperature and precipitation observation data and NCEP/NCAR atmospheric reanalysis data,this study evaluates the prediction of East Asian summer climate during 1959–2016 undertaken by the CESM(Community Earth System Model)large-ensemble initialized decadal prediction(CESM-DPLE)project.The results demonstrate that CESM-DPLE can reasonably capture the basic features of the East Asian summer climate and associated main atmospheric circulation patterns.In general,the prediction skill is quite high for surface air temperature,but less so for precipitation,on the interannual timescale.CESM-DPLE reproduces the anomalies of mid-and highlatitude atmospheric circulation and the East Asian monsoon and climate reasonably well,all of which are attributed to the teleconnection wave train driven by the Atlantic Multidecadal Oscillation(AMO).A transition into the warm phase of the AMO after the late 1990s decreased the geopotential height and enhanced the strength of the monsoon in East Asia via the teleconnection wave train during summer,leading to excessive precipitation and warming over East Asia.Altogether,CESM-DPLE is capable of predicting the summer temperature in East Asia on the interannual timescale,as well as the interdecadal variations of East Asian summer climate associated with the transition of AMO phases in the late 1990s,albeit with certain inadequacies remaining.The CESM-DPLE project provides an important resource for investigating and predicting the East Asian climate on the interannual and decadal timescales.

南太平洋副热带偶极子对中国气候影响的数值模拟

本文基于Hadley中心的海温数据集HadISST,利用EOF(Empirical Orthogonal Function)方法,分析了北半球冬季南太平洋副热带海温的特点,其第一模态呈现为马蹄型偶极子的空间分布(两个冷极中心和一个暖极中心),即为南太平洋副热带偶极模态(South Pacific Ocean Dipole,SPOD);其次采用通用地球系统模式(the Commuinty Earth System Model version1.0.4,简称CESM1.0.4)探讨了SPOD模态对中国冬夏气候的影响.数值试验结果表明,在北半球冬季,SPOD偶极模态可使中国华东和东北等地区的地表温度(Surface Temperature,TS)减小、海平面气压(Sea Level Pressure,SLP)升高,而在中国西南地区的TS、SLP分别增加和降低.与此同时,SPOD偶极模态通过海气相互作用可诱发低(高)层索马里越赤道气流(Somali Cross-Equatorial Flow,Somali CEF)和中国南海越赤道气流(South China Sea Cross-equatorial Flow)出现异常南(北)风、中国20°N—40°N附近的大气异常上升运动、水汽通量散度在中国华北和长江中下游地区异常辐合,从而引起该区域的降水增加.在北半球夏季,虽然SPOD偶极模态在衰退,但仍对中国区域的SLP、TS存在影响,且基本与冬季相反.此时SPOD偶极模态可使低(高)层索马里越赤道气流呈现北(南)风异常和中国南海越赤道气流呈现南(北)风异常、中国30°N、40°N附近大气的垂直运动分别呈现异常上升、下沉运动,从而水汽在华北附近区域为异常辐散、在华东至华南部分区域为异常辐合,这些可能是引起中国东部降水呈现北负南正的异常空间型的原因.

基于通用地球系统模式的不同类型气溶胶直接辐射效应的数值模拟

气溶胶可以通过直接效应来影响地气系统的辐射平衡,然而目前气溶胶直接辐射效应的研究主要集中于总气溶胶,缺乏不同类型气溶胶直接辐射效应研究。利用通用地球系统模式(Community Earth System Model,CESM)模拟研究了晴空和有云条件下总气溶胶、硫酸盐气溶胶和含碳气溶胶在大气层顶和地表的直接辐射强迫,并利用多源数据对模拟结果进行验证。结果表明,CESM模拟总气溶胶光学厚度与气溶胶自动观测网(Aerosol Robotic Network,AERONET)有较好的相关性(R^(2)=0.44),但模拟数值整体偏小;与MERRA-2(Modern-EraRetrospective Analysis for Research and Applications Version 2)对比发现,高估了含碳气溶胶光学厚度,低估了硫酸盐气溶胶光学厚度;CESM模拟的辐射通量与基线地表辐射观测网(Baseline Surface Radiation Network,BSRN)的模拟效果良好(R^(2)=0.93)。在晴空条件下,CESM模拟的总气溶胶以及硫酸盐气溶胶、含碳气溶胶在大气层顶的直接辐射强迫分别为-1.37、-0.46、-0.45 W/m^(2);有云条件下分别为-0.30、-0.25、+0.04 W/m^(2),云削弱了气溶胶在大气层顶负的辐射效应,但加强了含碳气溶胶的吸热作用从而呈现出正效应;晴空条件下地表的直接辐射强迫分别为-5.60、-0.53、-2.21 W/m^(2),有云条件下分别为-4.38、-0.32、-1.64 W/m^(2),气溶胶的直接辐射效应在地表均为负效应,云对沙尘气溶胶的辐射效应影响不大,但却能削弱硫酸盐气溶胶和含碳气溶胶的直接辐射效应强度。研究结果有利于进一步理解不同类型气溶胶的直接辐射效应,并为未来改进CESM提供依据。

过去2000年全球典型暖期特征与机制的模拟研究

本文利用美国国家大气研究中心（NCAR）的通用地球系统模式（Community Earth System Model,简称CESM）的低分辨率版本（CESM1.0.3,T31_g37）在国际国内率先进行了多组过去2000年瞬变积分模拟试验,在与历史重建资料和观测资料进行对比验证的基础上,对过去2000年中的典型暖期（中世纪暖期与现代暖期）的特征和成因机制进行了初步探讨,结果表明：中世纪暖期太阳辐射加强是导致其“暖化”的主要原因之一,而温室气体浓度的激增是现代全球变暖的最主要原因;在中世纪暖期,自然因子（包括太阳辐射和火山活动）对降水量的影响之和比温室气体的影响高一个数量级;而在现代暖期,温室气体对降水量的影响比自然因子（包括太阳辐射和火山活动）对降水量的影响之和高一个数量级;在不同外强迫条件下的海表温度变化在热带太平洋区域截然不同,即自然因子影响下为类-拉尼娜态,而温室气体影响下为类-厄尔尼诺态;无论在中世纪暖期还是现代暖期,相对于1000～1850年的平均情况,沃克（Walker）环流均处于增强状态.

Projection of weather potential for winter haze episodes in Beijing by 1.5℃ and 2.0℃ global warming

Haze episodes become very frequent in Beijing over the past decade,and such trend is related to favorable weather conditions.Here,we project the changes of weather conditions conducive to winter haze episodes in Beijing by 1.5℃ and 2.0℃ global warming using Haze Weather Index(HWI)and data of ensemble simulations from the Community Earth System Model(CESM)low-warming experiment.Compared to present day(2006–2015),the frequency in winter season is projected to increase by 14% for regular haze episodes(HWI>0)and 21% for severe haze episodes(HWI>1)at the 1.5℃ global warming.Projections shows larger increases of 27% for regular and 18%for severe haze events at the 2℃ global warming.The additional warming of 0.5℃ largely enhances the persistence of weather conditions conducive to haze episodes.The increased temperature contrast between near-surface and mid-troposphere in eastern Asia accounts for 57% and 81% of the change in HWI by 1.5℃ and 2℃ warming,respectively.Considering increased haze weather potential caused by climate warming,we suggest that additional efforts in emission reductions of carbon dioxide and air pollution are necessary to mitigate haze episodes in Beijing.