The response of the East Asian summer monsoon (EASM) system to reductions in emissions of anthropogenic aerosols and their precursors at the end of the twenty-first century projected by Representative Concentration Pathway 4.5 is studied using an aerosol-climate model with aerosol direct, semi-direct, and indirect effects included. Our results show that the global annual mean aerosol effective radiative forcing at the top of the atmosphere (TOA) is +1.45 W m(-2) from 2000 to 2100. The summer mean net all-sky shortwave fluxes averaged over the East Asian monsoon region (EAMR) at the TOA and surface increased by +3.9 and +4.0 W m(-2), respectively, due to the reductions of aerosols in 2100 relative to 2000. Changes in radiations affect local thermodynamic and dynamic processes and the hydrological cycle. The summer mean surface temperature and pressure averaged over the EAMR are shown to increase by 1.7 K and decreased by 0.3 hPa, respectively, due to the reduced aerosols. The magnitudes of these changes are larger over land than ocean, causing a marked increase in the contrast of land-sea surface temperature and pressure in the EAMR, thus strengthening the EASM. The summer mean southwest and south winds at 850 hPa are enhanced over eastern and southern China and the surrounding oceans, and the East Asian subtropical jet shifted northward due to the decreases of aerosols. These factors also indicate enhanced EASM circulation, which in turn causes a 10 % increase in summer mean precipitation averaged over the EAMR.
未来气候变化背景下Hadley环流变化是一个众所关注的问题。RCP4.5是中等程度的温室气体排放情景,到21世纪末全球增温介于2~3℃之间,这与中上新世暖期(距今约3百万年前)在全球增温方面非常相似,因此基于中上新世暖期和RCP4.5情景下Hadley环流变化特征的比较,揭示Hadley环流变化机理,并预估其气候影响,这对理解未来气候预估结果的不确定性有重要意义。本项目将首先比较参加中上新世模拟比较计划(PlioMIP1)的大气环流模式(AGCM)和耦合模式(CGCM)模拟的Hadley环流变化异同,在此基础之上,揭示主导中上新世暖期Hadley环流强度和边界变化的机理,并将其与主导RCP4.5情景下Hadley环流强度和边界变化的机理比较。与此同时,揭示中上新世暖期和RCP4.5情景下Hadley环流变化各自对东亚气候的影响,特别是阐明Hadley环流变化与EASM环流变化的联系。
2016-01