人为温室气体强迫下东亚-西太气候年际变率的变化机制

Increased anthropogenic green-house gases (GHG) concentration not only accounts for the increase of global temperature, but also impacts the mean state and variability of precipitation and atmospheric circulation. Based on the outputs of 30 coupled models from Coupled Model Intercomparison Project Phase 5 (CMIP5), the responses of the interannual climate variability over East Asia-West Pacific to anthropogenic GHG forcing will be assessed, including the amplitude of interannual variability of precipitation and atmospheric circulation and their relationship with tropical sea surface temperature (SST). And the mechanisms for the changes will be investigated. The contributions of specific humidity and atmospheric circulation to the changes in the interannual precipitation variability will be assessed, based on moisture budget analysis. The contributions of static stability and diabatic heating to the changes in the interannual variability of atmospheric circulation will also be assessed, based on linear baroclinic model experiment. Since the increased atmospheric CO2 concentration impacts the climate either by direct radiative forcing or indirectly by the warming of SST, we investigate how the relationship between East Asia-West Pacific climate with tropical SST anomaly is modulated by the direct radiative forcing of increased atmospheric CO2 concentration, the spatially uniform SST warming and the SST warming pattern, based on the idealized simulations by stand-alone atmospheric general circulation models participated in CMIP5. The current project aims at quantitatively revealing how and why the interannual climate variability over East Asia-West Pacific responds to anthropogenic GHG forcing, providing theoretical basis for mitigation and adaptation strategies.

人为温室气体浓度的升高不仅导致了全球气温上升，还会改变降水和大气环流的平均态和变率。本项目从第五轮耦合模式比较计划（CMIP5）提供的30个耦合模式的历史气候模拟试验和未来气候预估试验结果出发，定量揭示人为温室气体强迫下东亚-西太地区气候年际变率的变化规律，包括降水和大气环流的年际变率幅度变化及其与热带海温的关系的变化，在此基础上探讨其变化的机制。采用水汽收支方程定量诊断比湿和大气环流对降水年际变率变化的相对贡献，采用线性斜压模式定量诊断静力稳定度和非绝热加热率对大气环流年际变率变化的相对贡献。利用CMIP5提供的单独大气环流模式的理想试验，分别探讨仅存在大气CO2浓度升高的直接辐射强迫、平均态海温均匀增暖和平均态海温非均匀增暖的情形下，东亚-西太气候年际变率对热带关键区异常海温的依赖关系如何变化。本项目将定量揭示变暖背景下气候年际变率的变化规律和机制，为科学应对气候变化提供理论支撑。

年际气候变率是极端气候事件重要诱因，而ENSO是影响东亚-西太地区年际气候变率的关键信号。本项目利用参与国际耦合模式比较计划（CMIP5和CMIP6）的大量气候模式，定量地揭示了人为温室气体强迫下东亚-西太地区降水和大气环流年际变率的变化规律，构建了解释该地区年际气候变率幅度变化的简单理论模型，阐明了ENSO发展、成熟和衰减位相东亚-西太异常大气环流对人为温室气体强迫的响应机制，厘清了平均态SST变暖、SST空间结构变化和ENSO期间SSTA变化的相对贡献；揭示了人为温室气体强迫下大气静力稳定度的增强能够抑制ENSO异常热源触发的异常大气环流，阐明了为什么赤道太平洋的大气异常热源明显增强但东亚-西太的异常大气环流并非相应地增强。除了完成项目计划书设定的研究目标外，本项目还探索了平均态东亚夏季风对人为温室气体等外强迫的响应机制，揭示了青藏高原热力强迫是平均态东亚夏季风随着人为温室气体浓度升高而增强的关键机制；通过横向比较，阐明了间冰期轨道参数和COVID-19等其他外强迫因子影响东亚夏季风强度的机制差异及其对东亚降水格局的潜在影响。在本项目资助下，项目组共发表学术论文8篇，其中6篇发表在Journal of Climate，2篇发表在Climate Dynamics。本项目的成果不仅有助于更深入地理解年际气候变率对人为温室气体强迫的响应机制，还能够为应对气候变化和极端气候提供科学支撑，项目提出的主要机制已被IPCC第六次气候变化评估报告采用。