大气模式估算的东亚区域人为硫酸盐和黑碳气溶胶辐射强迫及其时间变化特征

本文利用大气环流模式及大气化学模式所得气溶胶资料,估算了相对1850s时期硫酸盐和黑碳气溶胶引起的全球及东亚区域人为辐射强迫,重点分析其在东亚区域的季节和长期变化特征.结果表明,就当前全球年平均全天空而言,人为硫酸盐气溶胶对大气顶的直接和云反照率强迫分别为-0.37和-0.98 W·m-2,黑碳气溶胶对大气顶和整层大气的辐射强迫值为0.16和0.47 W·m-2;中国东部区域是目前上述气溶胶辐射强迫最强的区域,硫酸盐的直接和间接辐射强迫分别超过-2.0和-4.0 W·m-2,黑碳对大气顶和整层大气的直接辐射强迫分别可达2.0和5.0W·m-2;估算的东亚区域上述气溶胶辐射强迫仍在不断增强,峰值预计出现在2010s时段,而且中国东部较强的辐射强迫还可能维持至2030s左右;在未来中、高排放情景下,东亚区域以上两种气溶胶预计对全球气溶胶辐射强迫有更大的贡献.分析还表明,夏季东亚区域较强的水汽会增强吸湿性硫酸盐气溶胶的光学厚度和晴空直接辐射强迫;云的作用一方面会强化东亚区域全天空条件下大气顶黑碳的辐射强迫,另一方面会影响硫酸盐气溶胶间接云反照率强迫的季节变化;上述气候特征的差异使得东亚区域的气溶胶辐射强迫表现出与欧美区域有所不同的特征.本文所用的气溶胶资料与模式气象场的偏差会给气溶胶辐射强迫计算带来一些不确定性,进一步改进气候模式中气溶胶过程、水汽和云等气象场的模拟将有助于获得更为合理的区域气溶胶辐射强迫估算结果.

Anthropogenic Eastern Asian radiative forcing due to sulfate and black carbon aerosols and their time evolution estimated by an AGCM

Aerosols play important roles in the climate system and one of key issues is to quantitatively investigate their radiative forcing (RF). Anthropogenic RF due to black carbon (BC) and sulfate relative to 1850 s is therefore investigated in this study using an atmospheric general climate model (AGCM) and the aerosol dataset simulated by an atmospheric chemistry transport model.To calculate the instantaneous aerosol RF, meteorological fields are simulated by the AGCM. The AGCM used in this study is developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences. The long-term three-dimensional black carbon and sulfate fields are taken from the simulation from the NCAR CAM Chemistry model. The dataset covers the period from the 1850s to 2100, and each 10-year set of results is averaged to produce the decadal mean. The decades of 1850—1859 and 2000—2009 represent the pre-industry (PI) and present day (PD), respectively. Cloud albedo forcing (CAF) is calculated from a diagnose scheme. The anthropogenic aerosols and the associated direct RF are estimated as the differences between a specified decade and the PI. The aerosol RF is obtained using a "double radiation call" method, in which the radiation scheme is called twice at each radiation time step. The GHGs, ozone, and solar forcing are fixed at present levels. The sea surface temperature and sea ice are from the prescribed climatology.This study shows that the present global annual mean anthropogenic sulfate all-sky direct and cloud albedo RF is estimated to be -0.37 and -0.98 W·m^-2, respectively; BC RF at all-sky top of atmosphere (TOA) and in the atmospheric column is calculated to be 0.16 and 0.47 W·m^-2, respectively. The present strongest RF due to above aerosols occurs in Eastern China, where sulfate direct and indirect RF exceeds -2.0 and -4.0 W·m^-2, respectively, and BC RF at TOA and column atmosphere is up to 2.0 and 5.0 W·m^-2, respectively. Furthermore, the estimated aerosol RF over East Asia still continuously increases and the maximum values are projected to occur in the 2010s. The projected stronger RF over Eastern China will even last until the 2030s. Thus, sulfate and BC from East Asia is projected to contribute more proportion to the global aerosol RF under future middle and high emission scenarios. The analysis in this study also indicates that the stronger summer atmospheric moisture over East Asia tends to intensify aerosol optical depth and direct clear-sky RF due to hydrophilic sulfate aerosol; moreover, cloud effects not only strengthen BC direct RF at all-sky TOA but also influence seasonal features of sulfate cloud albedo forcing over East Asia. Climatological characteristics over East Asia lead to the corresponding differences in aerosol RF compared to European and Northern American regions.The BC and sulfate RF and their possible time evolution are investigated in this paper. Many valuable results are obtained as mentioned above. However, the estimation of aerosol RF in the AGCM is determined by many factors and still faces large uncertainties. The first uncertainty arises from aerosol loading. Compared to surface measurements in Eastern China, the simulated BC and sulfate surface concentrations are much weaker and spatial correlations are also not high. These biases lead to our estimated present RF due to BC and sulfate likely lower than the actual values in East Asia. Other uncertainties are caused by simulated model meteorological fields and aerosol radiative parameterizations, such as atmospheric moisture, clouds and aerosol optical properties. So, it is suggested in our work that improvements of current climate models associated with aerosol processes and meteorological fields, which help to obtain more reasonable East Asian aerosol RF.