全球变暖不同阶段热带辐合带的移动及其与大气能量输送的关系

基于第五次国际间耦合模式比较计划(The phase 5 of the Coupled Model Intercomparison Project,CMIP5)中在4.5 W/m^2的典型浓度路径(Representative Concentration Pathway,RCP4.5)试验结果,本文通过能量框架分析方法研究了全球变暖不同阶段热带辐合带(Intertropical Convergence Zone,ITCZ)的南北移动及其主要机制,发现在温室气体持续增加的海洋快响应和温室气体达到稳定后的海洋慢响应两个阶段,ITCZ的移动都和跨赤道的大气能量输送(Atmosphere Heat Transport,AHT)变化显著相关,但两者变化的原因在两个阶段中是不同的。在快响应阶段,ITCZ位置的移动以及跨赤道AHT受大气层顶(Top of the Atmosphere,TOA)的能量变化驱动,主要与南大洋云短波辐射响应、北半球中高纬度云和地表的短波辐射响应有关,气溶胶减少引起的辐射响应变化使得ITCZ在大多数模式中表现出向北移动的特征。在慢响应下辐射强迫保持稳定,ITCZ在大多数模式中表现出向南移动的特征。这一时期ITCZ的移动由大气表面能量通量变化驱动,主要与潜热通量变化的南北半球差异有关。全球变暖不同阶段ITCZ移动与大气能量输送变化的关系差异反映了海洋对于气候变化的重要调控作用。

The Intertropical Convergence Zone Shift and Its Relationship with Atmospheric Energy Transport Change at Different Stages of Global Warming

Based on the outputs of 4.5 W/m^2 Representative Concentration Pathway(RCP4.5)in the phase 5 of the Coupled Model Intercomparison Project(CMIP5),we investigated the Intertropical Convergence Zone(ITCZ)shift and its main mechanism in different stages of global warming through the energetics framework analysis.The ITCZ shift is significantly correlated with the change of Atmosphere Heat Transport(AHT)across the equator both during the greenhouse gases transient increasing(the fast oceanic response)and after the greenhouse gases stabilizing(the slow oceanic response).However,the reasons for the cross-equatorial AHT change and the ITCZ shift are different in the two stages.In fast response,the ITCZ shift and the cross-equator AHT are mainly driven by the interhemispheric difference of the Top of the Atmosphere(TOA)fluxes,which is mainly related to the cloud shortwave radiative feedback in the southern ocean,and cloud shortwave radiative feedback plus surface albedo radiative feedback in the mid and high latitudes of the northern hemisphere.Due to the radiative response caused by the aerosols reduction,most models show that ITCZ shift northward.By contrast,in the slow response when the radiative forcing has stabilized,ITCZ shift southward in most models.This southward shift is mainly driven by the surface flux change,which is further related to the interhemispheric asymmetry of latent heat flux change.The difference in the relationship between ITCZ shift and atmospheric energy transport changes in different stages of global warming reflects the important role of ocean in regulating the climate system.