Evaluation of the Mechanisms Acting on the Atlantic Meridional Overturning Circulation in CESM2 for the 1pctCO_(2) Experiment

The Atlantic Meridional Overturning Circulation(AMOC)is a crucial component of the Earth’s climate system due to its fundamental role in heat distribution,carbon and oxygen transport,and the weather.Other climate components,such as the atmosphere and sea ice,influence the AMOC.Evaluating the physical mechanisms of those interactions is paramount to increasing knowledge about AMOC’s functioning.In this study,the authors used outputs from the Community Earth System Model version 2 and observational data to investigate changes in theAMOC and the associated physical processes.Two DECK experiments were evaluated:piControl and 1pctCO_(2),with an annual increase of 1%of atmospheric CO_(2).The analysis revealed a significant decrease in the AMOC,associated with changes in mixed layer depth and buoyancy in high latitudes of the North Atlantic,resulting in the shutdown of deep convection and potentially affecting the formation of North Atlantic Deep Water and Antarctic Bottom Water.A vital aspect observed in this study is the association between increased runoff and reduced water evaporation,giving rise to a positive feedback process.Consequently,the rates of freshwater spreading have intensified during this period,which could lead to an accelerated disruption of the AMOC beyond the projections of existing models.

Comparison Between GAMIL, and CAM2 on Interannual Variability Simulation

Recently, a new atmospheric general circulation model （GAMIL： Grid-point Atmospheric Model of IAP LASG） has been developed at the Institute of Atmospheric Physics （IAP）, Chinese Academy of Sciences （CAS）, which is based on the Community Atmospheric Model Version 2 （CAM2） of the National Center for Atmospheric Research （NCAR）. Since the two models have the same physical processes but different dynamical cores, the interannual variability simulation performances of the two models are compared. The ensemble approach is used to reduce model internal variability. In general, the simulation performances of the two models are similar. Both models have good per- formance in simulating total space-time variability and the Southern Oscillation Index. GAMIL performs better in the Eastern Asian winter circulation simulation than CAM2, and the model internal variability of GAMIL has a better response to external forcing than that of CAM2. These indicate that the improvement of the dynamic core is very important. It is also verified that there is less predictability in the middle and high latitudes than in the low latitudes.

Impacts of uncertain cloud-related parameters on Pacific Walker circulation simulation in GAMIL2

To investigate the impacts of uncertain parameters on simulated Pacific Walker circulation （PWC）, a large number of perturbed parameter simulations are conducted using GAMIL2 （the Grid-point Atmospheric Model of IAP/LASG, version 2）, and three different PWC indices are selected.The results show that the influences of some parameters on PWC are dependent on the selected index - a finding supported by the inconsistent responses of different indexes to these parameters. Among the nine parameters, the RH threshold for deep convection （RHCRIT） is the most sensitive in simulating PWC. Increased RHCRIT weakens deep convective heating and stratiform cooling, and strengthens shallow convective heating. Further analysis reveals that uncertain parameters affect the simulated PWC through changing the diabatic heating and vertical motion.

碳中和情景下人为排放对全球对流层臭氧的影响研究

本文采用地球系统模式,以未来碳中和排放清单和平流层示踪物O_(3)S为基础,揭示了未来对流层O_(3)及其前体物的变化特征及成因.研究结果表明:碳中和排放情景下,特别在冬春季节,全球范围内的NO_(x)人为排放和飞机排放量均显著降低,这使得近地面NO_(x)浓度随之降低.NO_(x)作为对流层O_(3)的重要前体物之一,其浓度的剧烈减少使得近地层O_(3)浓度显著降低,但在中国东部地区,由于NO对O_(3)滴定作用的减弱,最终使得冬季近地面O_(3)呈现增加趋势;垂直方向上O_(3)浓度减少最为显著的区域集中在对流层顶附近,减少量达26×10^(-9)以上,且夏季最为显著,这主要与飞机排放减少导致的平流层O_(3)浓度降低有关.碳中和排放情景下平流层入侵对全球近地面O_(3)的平均贡献减少量在冬季最高,为1.7×10^(-9),夏季最低,为0.9×10^(-9);北半球平流层入侵贡献减少量最显著区域集中在高纬地区,达4×10^(-9).垂直方向上,平流层入侵贡献减少量随高度增加,在对流层上层,平流层的贡献量降低高达24×10^(-9)以上,且冬季最强.总之,碳中和排放情景下地表人为排放及飞机排放的改变对全球O_(3)污染有很好的减轻作用,平流层贡献量的降低对未来O_(3)浓度的变化也有重要贡献.

BP神经网络在CESM强化密度及乳腺癌诊断中的研究分析

将穿刺活检或手术病理结果分析得到的乳腺肿瘤性质作为对比标签值,在χ^(2)检验的基础上,采取交叉验证确定超参数、独热编码处理输入信号等方法,使用Tensorflow深度学习框架建立两个BP神经网络,分别为不剔除交叉列联分析中χ^(2)值最小的强化密度属性的三输入信号网络与剔除该属性的两输入信号网络,利用两个网络分别对乳腺肿瘤性质进行诊断研究。通过对两个网络准确度、敏感度以及特异度的对比研究,发现强化密度对恶性肿瘤的检出率较高,引入强化密度的三输入信号网络模型为最佳模型;最佳模型与CESM检查技术结合的诊断精度可达95.77%;乳腺良、恶性肿瘤诊断最佳模型中敏感度与特异度的ROC曲线显示,最佳诊断参考点为(0.978,0.949)。

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.

A Coupled Experiment with LICOM2 as the Ocean Component of CESM1

In the present study, the LASG/IAP Climate system Ocean Model version 2 （LICOM2） was implemented to replace the original ocean component in the Community Earth System Model version 1.0.4 （CESM1） to form a new coupled model referred to as CESMI＋LICOM2. The simulation results from a 300-yr prein- dustrial experiment by using this model were evaluated against both observations and the Flexible Global Ocean-Atmosphere-Land System Model with grid-atmospheric model version 2 （FGOALS-g2）. It was found that CESMI＋LICOM2 simulates well the mean features of the ocean, sea ice, and atmosphere, relative to models used in the Coupled Model Intercomparison Experiment （CMIP5）, when compared with obser- vations. The spatial distribution of SST bias in CESMI＋LICOM2 is similar to that in the Community Climate System Model version 4 （CCSM4）. The simulated climate variabilities, such as ENSO and Pacific decadal oscillation, are also reasonably simulated when compared with observations. The successful implementation of LICOM2 in the CESM1 framework greatly enhances the capability of LICOM2 in conducting high-resolution simulations and model tuning. Compared with FGOALS-g2, the simulations of both SST and Atlantic meridional overturning circulation are significantly improved in CESMI^LICOM2. The former can be mainly attributed to the atmospheric model, and the latter to the improvement in the parameterization of diapycnal mixing. The study provides a base to further improve the present version of LICOM and its functionalities in the coupled model FGOALS at both low and high resolutions.

西北太平洋热带气旋潜势分布和年际变率的数值模拟

热带气旋潜势指数是定量表征影响热带气旋生成的大尺度环境条件指标,在不能显式模拟热带气旋的气候系统模式中,常被作为热带气旋的代用指标。基于中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室发展的AGCM GAMIL2.0模式在历史海温驱动下的积分结果,评估了该模式对热带气旋潜势气候态、季节循环和年际变率的模拟能力。并分别从影响热带气旋潜势分布的热力因子(相对湿度、热带气旋最大风速)和动力因子(垂直风切变、绝对涡度、垂直抬升速度)的角度,讨论了造成热带气旋潜势模拟误差的原因。结果表明,在西北太平洋地区,模式能够合理再现热带气旋潜势的气候态分布,但由于GAMIL2.0模拟的相对湿度偏大且向东延伸,造成了热带气旋潜势大值区较之再分析资料偏大且偏东10°。由于GAMIL2.0模拟的季风槽位置偏北偏强,导致模拟的热带气旋潜势季节循环北进偏早而南退偏晚。在年际变化方面,GAMIL2.0能合理模拟出热带气旋潜势在ENSO正负位相东西反向的变化特征,但位于20°—30°N的加强和减弱区的分界线偏西,这与模拟的垂直速度和相对湿度的模拟误差有关,进一步分析表明,这是由于模拟中ENSO事件期间的西北太平洋异常上升中心比观测偏西且偏强造成的。

Arctic ozone loss in early spring and its impact on the stratospheretroposphere coupling

The tropospheric impact of Arctic ozone loss events is still debatable.In this study we investigate that question,using the ERA5 reanalysis and long-term integration by a climate-chemistry coupled model(CESM2-WACCM).We begin with the frequency of Arctic ozone loss events.On average,such events occur once in early spring every 14−15 years in ERA5 data and in the model,both of which estimate that roughly 40%of the strong polar vortex events in March are coupled with Arctic ozone loss,the remaining 60%being uncoupled.The composite difference between the two samples might be attributed to the pure impact of the Arctic ozone loss-that is,to ozone loss alone,without the concurrent impact of strong polar vortices.Arctic ozone loss is accompanied by an increase in total ozone in midlatitudes,with the maximum centered in the Central North Pacific.Contrasting Arctic ozone loss events with pure strong polar vortex events that are uncoupled with ozone loss,observations confirm that the stratospheric Northern Annular Mode reverses earlier for the former.For pure strong vortex events in early spring(without Arctic ozone loss),the cold anomalies can extend from the stratosphere to the middle troposphere;when such events are strong,the near surface warm anomalies are biased toward the continents.In contrast,during the other 40%of strong early-spring polar vortex events,those coupled with ozone loss,a concurrent and delayed warming of the near surface over the Arctic and its neighboring areas is observed,due to vertical redistribution of solar radiation by the change in the ozone.

Comparison of the Anthropogenic Emission Inventory for CMIP6 Models with a Country-Level Inventory over China and the Simulations of the Aerosol Properties

Anthropogenic emission inventory for aerosols and reactive gases is crucial to the estimation of aerosol radiative forcing and climate effects.Here,the anthropogenic emission inventory for AerChemMIP,endorsed by CMIP6,is briefly introduced.The CMIP6 inventory is compared with a country-level inventory(i.e.,MEIC)over China from 1986 to 2015.Discrepancies are found in the yearly trends of the two inventories,especially after 2006.The yearly trends of the aerosol burdens simulated by CESM2 using the two inventories follow their emission trends and deviate after the mid-2000s,while the simulated aerosol optical depths(AODs)show similar trends.The difference between the simulated AODs is much smaller than the difference between model and observation.Although the simulated AODs agree with the MODIS satellite retrievals for country-wide average,the good agreement is an offset between the underestimation in eastern China and the overestimation in western China.Low-biased precursor gas of SO_(2),overly strong convergence of the wind field,overly strong dilution and transport by summer monsoon circulation,too much wet scavenging by precipitation,and overly weak aerosol swelling due to low-biased relative humidity are suggested to be responsible for the underestimated AOD in eastern China.This indicates that the influence of the emission inventory uncertainties on simulated aerosol properties can be overwhelmed by model biases of meteorology and aerosol processes.It is necessary for climate models to perform reasonably well in the dynamical,physical,and chemical processes that would influence aerosol simulations.

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.

Reducing the climate shift in a new coupled model

Climate drift refers to spurious long-term changes that may be inherent in coupled models when external forcing factors are fixed. Understanding the sources of this drift and tuning the drift are crucial for obtaining reasonable simulations from coupled models. To prepare for the upcoming Coupled Model Intercomparison Project Phase 6, a new coupled model has been constructed based on the Community Earth System Model and the Grid-point Atmospheric Model of IAP LASG version 2. However, the surface temperature predicted by the new model is too underestimated, and this underestimation is caused by a type of climate drift, i.e., ‘‘initial shock.'' This study analyzes the source of the cold surface temperature from the perspective of energy balance and attempts to reduce the surface temperature drift by tuning the relative humidity threshold for low cloud.

决定北半球冬季哈得莱环流年际变率的三维大气环流图像:观测分析和数值模拟

本文利用NCEP/NCAR再分析资料,分析了1979~2008年北半球冬季哈得莱(Hadley)环流年际变化的特征,在此基础上,讨论了在观测海温驱动下大气环流模式的模拟结果.观测分析表明,近30年北半球冬季哈得莱环流年际变率的主导模态呈现出空间上的非均匀变化,哈得莱环流圈位于热带部分与其位于副热带部分的强度变化符号相反,这在表征其年际变化特征的另一指标——经向风垂直切变中亦有显著体现.大气环流模式AMIP积分试验结果表明,北半球冬季哈得莱环流强度的上述年际变化源于海温强迫.分析发现,热带中东太平洋和南印度洋暖海温距平强迫导致了哈得莱环流强度年际变化的主导模态呈现出空间上的非均匀变化.ElNio的局地作用和大气桥作用激发的太平洋局地哈得莱环流(30°S^30°N,150°E^90°W)和大西洋局地哈得莱环流(30°S^30°N,90°W^10°W)并非呈现出整体一致的变化,尽管二者纬向平均后分别使气候平均的哈得莱环流圈强度加强和减弱.ElNio遥强迫作用激发的西北太平洋反气旋(0°~30°N,100°E^150°E)使北半球Hadley环流圈强度减弱,ElNio和南印度洋暖海温距平共同强迫出的南印度洋反气旋(30°S^0°,60°E^100°E)使南半球Hadley环流圈的强度亦减弱.上述局地哈得莱环流的变化叠加后,因纬向平均的太平洋局地哈得莱环流强度在(副)热带部分的增强大(小)于纬向平均的大西洋局地哈得莱环流和西北太平洋、南印度洋局地哈得莱环流在(副)热带地区的减弱,结果使得哈得莱环流圈的强度在(副)热带部分偏强(弱);较之南半球,北半球强度变化稍强.因此,北半球冬季哈得莱环流年际变率的主导模态在空间上呈现出非均匀变化.

Reducing the biases in shortwave cloud radiative forcing in tropical and subtropical regions from the perspective of boundary layer processes

Biases in shortwave cloud radiative forcing(SWCF), which cause overestimates in tropical regions and underestimates in subtropical marine stratocumulus regions, are common in many climate models. Here, two boundary layer processes are investigated in the atmospheric model GAMIL2, entrainment at the top of the boundary layer and longwave radiative cooling at the top of stratocumulus clouds, in order to reduce biases and reveal the mechanisms underlying these processes. Our results show that including the entrainment process in the model can reduce negative SWCF biases in most tropical regions but increases positive SWCF biases in subtropical marine stratocumulus regions. This occurs because entrainment reduces the low-level cloud fraction and its cloud liquid water content by suppressing the vertical turbulent diffusion in the boundary layer and decreasing the relative humidity when warm and dry free atmosphere is entrained in the boundary layer. Longwave radiative cooling at the top of stratocumulus clouds can enhance turbulent diffusion within the stratocumulus-topped boundary layer. When combined with the entrainment process, longwave radiative cooling reduces the positive SWCF biases in subtropical marine stratocumulus regions that are observed using the entrainment process alone. The incorporation of these two boundary layer processes improves the simulated SWCF in tropical and subtropical regions in GAMIL2.