史湘军 1朱寿鹏 2智协飞 3杜康云 1刘庆爱 1王琳玮3
作者信息
- 1. 南京信息工程大学 气象灾害教育部重点实验室/气候与环境变化国际合作联合实验室/气象灾害预报预警与评估协同创新中心/东亚季风与区域气候变化科技创新团队,江苏南京210044
- 2. 中国科学院大气物理研究所LASG实验室,北京100029
- 3. 河北省气象局气候中心,河北石家庄050021
- 折叠
摘要
Abstract
The ultimate purpose of this study is to investigate the contribution of ice nucleation parameterizations to the difference in estimating anthropogenic aerosol indirect forcing.Three physically-based ice nucleation parameterizations,respectively developed by Liu and Penner(2005,hereafter LP),Barahona and Nenes (2009,hereafter BN)and K(a)ircher et al.(2006,hereafter KL) are analyzed in this paper.The LP parameterization is derived from fitting the simulation results of a cloud parcel with constant updraft velocities.The number of nucleated ice crystals is a function of relative humidity,temperature,aerosol number concentration and updraft velocity.The BN parameterization is derived from an approximation to the analytical solution of air parcel equations.One advantage of BN parameterization is that the heterogeneous nucleation may be described by different nucleation spectra,derived either from the classical nucleation theory,or from observations.In KL parameterization,the competition between different freezing mechanisms is treated by explicitly calculating the evolution of the water vapor saturation ratio within one host-model's time step.It is worth noting that,in this parameterization,the ice crystal number concentration produced via homogeneous freezing is not sensitive to the sulfate aerosol number concentration in most cases,except for the highest(4 m · s-1) updraft velocities.The offline experiments show that the ice crystal number concentration calculated from KL parameterization was not sensitive to sulfate aerosols number concentration in most cases,whereas the ice crystal number concentration calculated from the LP and BN parameterizations increased with the increasing sulfate aerosols number concentration.Compared to the BN and KL parameterizations,it is relatively easy for heterogeneous ice nucleation to inhibit homogeneous ice nucleation with LP parameterization.However,the ice crystal number concentration calculated from LP parameterization is usually higher than BN and KL parameterizations.Aside from the default LP parameterization in the CAM5 model,the BN and KL parameterizations were implemented in CAM5 for comparison.The occurrence frequency of homogeneous freezing from simulation with LP parameterization is less than BN and KL parameterizations.However,all of the simulations show that the occurrence frequency of homogeneous freezing is less than 0.1,which is in consistent with the observations.Furthermore,there is no remarkable difference among these three parameterizations in the ice crystal number concentration or cloud radiative forcing,and all of the simulation results show generally high agreements with cirrus cloud observations.This suggests that the model's capability to simulate cirrus clouds is not sensitive to physically-based ice nucleation parameterizations.The CAM5 experiment using the KL parameterization predicts a much smaller anthropogenic aerosol long wave indirect forcing(LWCF,0.05 W · m-2) than that using the LP(0.36 W · m-2) and BN(0.33 W · m-2)parameterizations.This indicates that ice nucleation parameterization plays an important role in estimating anthropogenic aerosol indirect forcing.Previous studies showed that the annual globaI mean change in LWCF from preindustrial times to present-day estimated from the ECHAM5 model with KL parameterization was 0.05-0.20 W · m-2,which was much less than the estimate(0.40-0.52 W · m-2) given by the CAM5 model with LP parameterization.It appears that this difference can be mostly explained by ice nucleation parameterizations.关键词
冰晶核化/参数化方案/气候模式/气溶胶间接效应/对比分析Key words
icenucleation/parameterization/climate model/aerosol indirect effect/sensitivity
