对全球气候模式中卷云纵向分布的评估及参数化发展

Climate prediction using computer models has many uncertain factors, but one of the key uncertainties is the treatment of clouds.Clouds have a huge influence on the radation reaching the Earth from the Sun and leaving the Earth-atmosphere system.Cirrus clouds are the cold clouds that exist at the upper levels of our atmosphere where the weather occurs (troposphere) and have an important influence on the balance not only of the solar radiation reaching the Earth but also the infrared heat being lost back to space.Small changes in these clouds can easily equal the anthropogenic forcing by CO2 since the start of the industrial revolution or a doubling of CO2.These ice clouds have particles in them that are varied in shape and sizes and in recent years there has been a move of climate modellers to treat the radiation by these clouds with more realistic ice shapes and this work is on-going now.In a recent publication by me I have shown that using observations of real ice clouds complemented with high resolution computer models that the observed vertical structure of ice clouds can easily equal the effects such as habits which are now being implemented and in the cases studied it showed that it counteracted the top of the atmosphere effects of habits that are being implemented and enhanced the surface effects.With climate models being currently updated with these habit effects now, it is essential that we fully explore the effects of vertical structure of habits and size distrbutions and develop a parameterisation for climate models so that the radiative effects of high cold clouds can be improved. ..In this reserach project we are seeking to expand the fully develop the result in Yang et al. (2011). The initial work was for one cloud observations.We will expand that to a set of cases covering results from mid-lat through to tropical deep convective anvil outflow cases. We will focus on cases that tested the range of cirrus produced not only regionally but also in terms of the cloud optical depth (a key measure of the potential of the cloud to affect the radiation).Developing this important result to be tested on observations in various locations around the globe will quantify how widespread the effect is and will allow us to understand it dependencies on region, cloud depth, formation mechanism, etc.With this information and expanding the results to include sensitivities gained through computer modelling of the cases, we will then be in a position to develop the parameterisation of vertical structure for climate models.We envision this parameterisation to have dependence on such factors as formation mechanism, optical depth, and/or potentially updraft speed of cloud formation or other factors that arise during the research.

项目申请人近期关于卷云的研究(Yang et al.,2011)给出了冰晶颗粒形态和数密度的纵向分布对全球辐射平衡有重要的影响。本项目将基于以上发现，根据地点、形成机制、光学厚度等不同因素，全球范围内选取建立多个卷云案例，从而对卷云内冰水含量、冰晶形态、数密度等的纵向分布的普遍性与可能性进行分析归类。对纵向分布对不同参数（光学厚度等）的敏感性进行评估。基于选取的卷云案例，应用LEM模式耦合Fu-Liou辐射模式，对相关参数变量（冰水含量、冰晶形态、数密度、分布的层数等）的纵向分布对辐射强度的影响进行敏感性测试，从而为全球气候模式GCMs中的纵向分布进行参数化发展。应用全球气候模式GCMs，更新所获得的纵向分布的参数变量，进行长期的气候模拟，从而得到纵向分布参数变量对全球辐射平衡及气候反馈的定量化影响。本项目的顺利完成，将模式中对卷云的认识模拟提高到一个全新的水平。

卷云对全球辐射平衡有重要的影响，更可以进一步影响长期的气候变化(Liou 1986; Min et al. 2011)。卷云由冰晶组成，目前，卷云中冰晶属性如何影响辐射还有待进一步研究。辐射模式中关于冰晶影响辐射的因素也在不断的增加，例如，habit、roughness etc(Baran & Labonnote 2007; Huiyi Yang et al. 2012; Garrett et al. 2001)。 本项目提出一项新的影响因素，卷云内部habit和数密度的纵向分布对辐射的影响。基于不同纬度、不同形成机制等，对8个卷云案例进行分析。结果显示，纵向分布对卷云的辐射平衡有重要影响。比较目前通用的fix effect radius辐射模式，和包含habit和数密度纵向分布等特征的辐射模式，upward 和downward辐射差别都达到100Wm－2以上。当缺少habit特征时，在TOP，upward辐射有10Wm－2的不同，在surface，downward辐射有大约20Wm－2的不同。当fix effective radius相对较小时（e.g. 20um），相对于较大的effective radius（e.g. 80um），卷云发展所持续的时间会被严重低估，IWP差距可以达到10倍以上。项目在原计划外进行了两点初步研究。第一，Residential emission所产生的PM2.5对五种呼吸相关疾病的影响。结果显示，Residential emission在东亚，南亚和东欧对PM2.5贡献最大。全球30岁以上成年人额外死亡率大约308,000人。中国和印度大约占50%。第二，气候变化和geoengineering对粮食安全的潜在影响。相对于global warming scenario，在geoengineering scenario下，yield下降10-15%。粮食生产的稳定性在future scenarios下增加。相对于historical scenario，crop failure在national level和regional level下，分别降低70%和20%。