基于CMIP6强迫模拟分析人为气溶胶的气候效应(二) ——诊断方法在分类评估中的重要性
投稿时间:2018-09-19  修订日期:2019-01-14  点此下载全文
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作者单位E-mail
史湘军 南京信息工程大学 shixj@nuist.edu.cn 
刘娇娇 南京信息工程大学  
智协飞 南京信息工程大学  
朱寿鹏 南京信息工程大学  
吉璐莹 南京信息工程大学  
张海鹏 南京信息工程大学  
沈沛洁 南京信息工程大学  
基金项目:国家重点研发计划(2017YFA0604000);国家自然科学基金资助项目(41775095);南京信息工程大学人才启动经费(2243141601067)
中文摘要:本研究通过详细阐述第六次耦合模式比较计划(Coupled Model Intercomparison Project Phase 6,CMIP6)给出的人为气溶胶强迫在模式中怎样影响大气顶(Top of Atmosphere,TOA)辐射通量,进而对气溶胶气候效应开展分类评估并探讨诊断方法的合理性。人为气溶胶辐射效应对计算云辐射强迫的影响为0.38 W?m?2。诊断评估气溶胶对云辐射强迫的影响需要排除这个偏差。两种基于不同试验设计诊断得出的半直接效应分别为0.21 和0.09 W?m?2,存在显著差异。主要原因可能是人为气溶胶影响云辐射强迫的不同机制之间在模式模拟过程中不断地相互交织,不是简单的线性叠加关系。模式诊断得出的Twomey效应不仅包括Twomey效应本身,还包括Twomey效应引起的部分快速调整。总之,利用模式评估分析人为气溶胶气候效应往往比预想的复杂,需要注意审查试验设计和诊断方法的合理性。
中文关键词:CMIP6; 人为气溶胶强迫; Twomey效应  半直接效应  分类评估;诊断方法
 
A Modeling Study on Anthropogenic Aerosol Effects Based on CMIP6 Forcing. Part II: Calculation Methods are important for Classification Analysis
Abstract:This study illustrates how does aerosol affect the top of atmosphere (TOA) radiation flux in the NUIST model using a hypothetical anthropogenic aerosol forcings given by Coupled Model Intercomparison Project Phase 6. There are three ways by which anthropogenic aerosol affect TOA radiation flux. Firstly, anthropogenic aerosol affects TOA radiation flux through the changes in aerosol optical properties, so-called aerosol radiative effect. This effect mainly depends on anthropogenic aerosol radiative forcing and is not related to Twomey effect. Secondly, anthropogenic aerosol affects TOA radiation flux through the changes in cloud optical properties, so-called aerosol effects on cloud radiative forcing. These effects include Twomey effect and semi-direct effect. Finally, anthropogenic aerosol affects TOA radiation flux through the changes in other optical factors. Compared with the first two ways, this way is negligible. This study focuses on the second way and discusses the methods used for estimating anthropogenic aerosol effects. In order to distinguish contributions to aerosol effects on cloud radiative forcing from semi-direct effect and indirect effect, we add two experiments: Rad and Tmy. Rad experiment only takes the anthropogenic aerosol optical properties into account. Tmy experiment only considers the anthropogenic aerosol Twomey effect. Including the experiments used in Part 1, there are four experiments: Base, Rad, Tmy, and Both. Rad and Base experiments results show that anthropogenic aerosol semi-direct effect is estimated at 0.21 W?m?2. Semi-direct effect could also be obtained as the difference between the aerosol effects on cloud radiative forcing from Both and Base experiments (i.e., semi-direct effect and Twomey effect) and the aerosol effects on cloud radiative forcing from Tmy and Base experiments (i.e., Twomey effect). This semi-direct effect is 0.09 W?m?2, significantly less than that from Bad and Base experiments. The difference between Tmy and Base experiments shows that the effective radiative forcing (ERF) caused by anthropogenic aerosol Twomey effect is ?0.22 W?m?2. The difference between Both and Rad experiments shows that the ERF caused by Twomey effect is ?0.30 W?m?2, which is stronger (more negative) than that from the difference between Tmy and Base experiments. It is clear that assessment results depend on experimental design. One probably reason is that aerosol semi-direct effect and indirect effect interact in a very complex way and the assumption about linear superposition is not reasonable. It is worth to note that the diagnosed Twomey effect is not only the Twomey effect itself but also cloud-relevant adjustments caused by Twomey effect. Aerosol could make an obvious impact on quantifying cloud forcing because aerosol also can scatter and absorb solar radiation. The short wave cloud forcing (SWCF) from Base experiments is ?47.54 W?m?2. Under no-aerosol condition, the SWCF* (i.e.,SWCF calculated as a diagnostic with aerosol scattering and absorption neglected) from Base experiment is ?49.51 W?m?2. The difference caused by the impact of aerosol is 1.98 W?m?2. Compared to Base experiment, this difference from Rad experiment is increased by 0.38 W?m?2 because anthropogenic aerosol is considered. In other words, for the same cloud optical properties, the SWCF diagnosed with aerosol optical properties could be increased by ~0.38 W?m?2 after considering anthropogenic aerosol optical properties. Because of this obvious positive bias, aerosol effects on cloud radiative forcing must be estimated from the change in SWCF* (diagnosed with aerosol scattering and absorption neglected), rather than SWCF (diagnosed using traditional method).
keywords:CMIP6  Anthropogenic Aerosol Forcing  Twomey effect  Semi-direct effect  Classification Analysis  Calculation Methods
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