The FGOALS climate system model as a modeling tool for supporting climate sciences:An overview

Climate system models are useful tools for understanding the interactions among the components of the climate system and predicting/projecting future climate change. The development of climate models has been a central focus of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences(LASG/IAP) since the establishment of the laboratory in 1985. In China, many pioneering component models and fully coupled models of the climate system have been developed by LASG/IAP. The fully coupled climate system developed in the recent decade is named FGOALS(Flexible Global Ocean-Atmosphere-Land System Model). In this paper, an application-oriented review of the LASG/IAP FGOALS model is presented. The improved model performances are demonstrated in the context of cloud-radiation processes, Asian monsoon, ENSO phenomena, Atlantic Meridional Overturning Circulation(AMOC) and sea ice. The FGOALS model has contributed to both CMIP5(Coupled Model Intercomparison Project-phase 5) and IPCC(Intergovernmental Panel on Climate Change) AR5(the Fifth Assessment Report). The release of FGOALS data has supported the publication of nearly 500 papers around the world. The results of FGOALS are cited ~106 times in the IPCC WG1(Working Group 1) AR5. In addition to the traditional long-term simulations and projections, near-term decadal climate prediction is a new set of CMIP experiment, progress of LAGS/IAP in the development of nearterm decadal prediction system is reviewed. The FGOALS model has supported many Chinese national-level research projects and contributed to the national climate change assessment report. The crucial role of FGOALS as a modeling tool for supporting climate sciences is highlighted by demonstrating the model's performances in the simulation of the evolution of Earth's climate from the past to the future.

Long-term change in low-cloud cover in Southeast China during cold seasons

中国东南地区在冬春冷季节盛行低云,对局地能量平衡和水文循环有重要的作用.本研究使用多套数据和数值模拟结果,分析这一地区冷季节内低云云量在1980年至2017年的长期变化.结果表明,低云云量经历了先下降后上升的趋势变化,转折点出现在2008年左右.局地水汽通量输送在影响低云云量的变化中起着至关重要的作用,其在冬季和春季分别受到哈德莱环流和沃克环流的影响.CMIP6中的气候模式对水汽通量输送的模拟能力欠佳,影响了对低云云量的模拟结果.

Climate Sensitivity and Feedbacks of a New Coupled Model CAMS-CSM to Idealized CO_2 Forcing: A Comparison with CMIP5 Models

Climate sensitivity and feedbacks are basic and important metrics to a climate system. They determine how large surface air temperature will increase under CO_2 forcing ultimately, which is essential for carbon reduction policies to achieve a specific warming target. In this study, these metrics are analyzed in a climate system model newly developed by the Chinese Academy of Meteorological Sciences(CAMS-CSM) and compared with multi-model results from the Coupled Model Comparison Project phase 5(CMIP5). Based on two idealized CO_2 forcing scenarios, i.e.,abruptly quadrupled CO_2 and CO_2 increasing 1% per year, the equilibrium climate sensitivity(ECS) and transient climate response(TCR) in CAMS-CSM are estimated to be about 2.27 and 1.88 K, respectively. The ECS is near the lower bound of CMIP5 models whereas the TCR is closer to the multi-model ensemble mean(MME) of CMIP5 due to compensation of a relatively low ocean heat uptake(OHU) efficiency. The low ECS is caused by an unusually negative climate feedback in CAMS-CSM, which is attributed to cloud shortwave feedback(λSWCL) over the tropical Indo-Pacific Ocean.The CMIP5 ensemble shows that more negative λSWCL is related to larger increase in low-level(925–700 hPa)cloud over the tropical Indo-Pacific under warming, which can explain about 90% of λSWCL in CAMS-CSM. Static stability of planetary boundary layer in the pre-industrial simulation is a critical factor controlling the low-cloud response and λSWCL across the CMIP5 models and CAMS-CSM. Evidently, weak stability in CAMS-CSM favors lowcloud formation under warming due to increased low-level convergence and relative humidity, with the help of enhanced evaporation from the warming tropical Pacific. Consequently, cloud liquid water increases, amplifying cloud albedo, and eventually contributing to the unusually negative λSWCL and low ECS in CAMS-CSM. Moreover, the OHU may influence climate feedbacks and then the ECS by modulating regional sea surface temperature responses.

The Asymmetric Effects of El Ni?o and La Ni?a on the East Asian Winter Monsoon and Their Simulation by CMIP5 Atmospheric Models

E1 Nifio-Southem Oscillation （ENSO） events significantly affect the year-by-year variations of the East Asian winter monsoon （EAWM）. However, the effect of La Nifia events on the EAWM is not a mirror image of that of E1 Nifio events. Although the EAWM becomes generally weaker during El Nifio events and stronger during La Nifia winters, the enhanced precipitation over the southeastern China and warmer surface air temperature along the East Asian coastline during E1 Nifio years are more significant. These asymmetric effects are caused by the asymmetric longitudinal positions of the western North Pacific （WNP） anticyclone during El Nifio events and the WNP cyclone during La Nifia events; specifically, the center of the WNP cyclone during La Nifia events is westward-shifted relat- ive to its El Nifio counterpart. This central-position shift results from the longitudinal shift of remote E1 Nifio and La Nifia anomalous heating, and asymmetry in the amplitude of local sea surface temperature anomalies over the WNP. However, such asymmetric effects of ENSO on the EAWM are barely reproduced by the atmospheric models of Phase 5 of the Coupled Model Intercomparison Project （CMIP5）, although the spatial patterns of anomalous circula- tions are reasonably reproduced. The major limitation of the CMIP5 models is an overestimation of the anomalous WNP anticyclone/cyclone, which leads to stronger EAWM rainfall responses. The overestimated latent heat flux an- omalies near the South China Sea and the northern WNP might be a key factor behind the overestimated anomalous circulations.

Responses of Cloud-Radiative Forcing to Strong El Nino Events over the Western Pacific Warm Pool as Simulated by CAMS-CSM

Cloud-radiative forcing(CRF)at the top of the atmosphere(TOA)over the western Pacific warm pool(WP)shows unique characteristics in response to El Nino events.In this region,the responses of CRF to El Nino events have been a useful metric for evaluating climate models.Satellite data are used to analyze the CRF anomalies to El Nino events simulated by the new and old versions of the Climate System Model of the Chinese Academy of Meteorological Sciences(CAMS-CSM),which has participated in the Atmospheric Model Intercomparison Project(AMIP).Here,simulations for super El Nino years,El Nino years,and normal years are compared with observations.The results show that the mean values of both longwave CRF(LWCRF)and shortwave CRF(SWCRF)in CAMS-CSM are weaker than the observations for each category of El Nino events.Compared with the old version of CAMS-CSM,the decrease in LWCRF during El Nino events is well simulated by the new version of CAMS-CSM.However,both new and old models cannot reproduce the anomalous SWCRF in El Nino events.The biases in the CRF response to El Nino events are attributed to the biases in the cloud vertical structure because of a weaker crash of the Walker circulation in CAMS-CSM.Due to the modification of the conversion rate from cloud droplets to raindrops in the cumulus convection scheme,the new version of CAMS-CSM has better CRF skills in normal years,but biases in El Nino events still exist in the new version.Improving the response of the Walker circulation to El Nino events is key to higher skills in simulating the cloud radiative responses.