基于偏振反演粒子形状参数改进气溶胶辐射强迫估算

Aerosol particle shape directly affects the spatial distribution of intensity and state of polarization of the scattered light, thereby changing the aerosol direct radiative forcing. The radiative forcing of dust aerosols can be severely underestimated based on the assumption of spherical particles. How to accurately obtain the shape parameters is the key to improve the estimation of aerosol direct radiative forcing with the presence of non-spherical particles mainly composed of dusts. Compared with intensity, polarization is more sensitive to particle shape. At present, there are still large uncertainty in the sphericity parameter retrieved from polarimetric measurements within the worldwide AErosol RObotic NETwork (AERONET) and the Chinese Sun/sky-radiometer Observation NETwork (SONET). The fact that dust particle shape distribution based on laboratory measurement cannot reflect the actual status of atmosphere is the most important issue to be dealt with for improving the retrieval. In this project, we plan to obtain the actual atmospheric dust particle shape distribution by sampling and fluorescence microscopy, then focus on improving the retrieval of the shape parameter based on the polarization observations by using the measured shape distribution model. It is aim to reduce the uncertainty of sphericity, and to improve the accuracy of inversions of the aerosol optical thickness, single scattering albedo, asymmetry factor, and the angström exponent simultaneously, then to improve the estimation of aerosol direct radiative forcing. The effects of particle non-sphericity on radiative forcing under different dust proportions will also be systematically analyzed in this project. It will provide significant supports for the researches on aerosol climate effects and global change.

气溶胶形状直接影响散射光强度的空间分布和偏振态，从而改变气溶胶直接辐射强迫。基于球形假设会导致沙尘辐射强迫被严重低估，如何准确获取形状参数是改进以沙尘为主的非球形粒子存在情况下气溶胶直接辐射强迫估算的关键。与强度相比，偏振对形状更加敏感。目前全球气溶胶自动观测网（AERONET）和中国太阳-天空辐射计观测网（SONET）偏振反演的球形度参数仍存在很大不确定性。反演中采用的实验室测得的沙尘形状谱不能反映实际大气状况，是改进反演需首要解决的问题。本项目基于采样和荧光显微测量获取实际大气沙尘形状谱分布，重点研究利用实测的形状谱模型改进形状参数的偏振反演，旨在降低球形度反演的不确定度，同时提高气溶胶光学厚度、单次散射反照率、不对称因子和Angström指数的反演精度，以改进气溶胶直接辐射强迫估算，并系统分析不同沙尘比例下粒子非球形性对辐射强迫的影响。为气溶胶气候效应和全球变化等研究提供重要支持。

本项目重点围绕气溶胶直接辐射强迫估算问题，以改进沙尘为主的非球形粒子存在情况下的气溶胶直接辐射强迫估算为目标，在新疆喀什沙尘源区附近和北京远距离传输沙尘条件下分别开展了多次沙尘气溶胶样本采集实验，基于实验室荧光显微测量分析建立了中国北方地区典型沙尘气溶胶形状谱分布模型。利用实测获得的气溶胶形状谱分布模型，构建非球形沙尘粒子群光散射查找表，并耦合到大气矢量辐射传输模型中。实现基于典型沙尘形状谱分布的天空光偏振正演模拟，开展大气气溶胶粒子形状谱分布对天空光偏振影响分析，并基于中国太阳-天空辐射计观测网SONET的天空光偏振测量，将实测的沙尘形状谱分布用于球形度等参数的反演。最后，综合细化考虑气溶胶非球形特性、地表反照率日变化、以及大气温、湿、压和臭氧垂直廓线变化因素，有效改进沙尘等非球形粒子存在情况下气溶胶辐射强迫的估算。建立了考虑非球形气溶胶的中国区站点十年气溶胶辐射强迫估算数据集，并进行不同类型站点气溶胶辐射强迫十年尺度长期变化趋势分析，可为基于模式的年代际气候变化模拟和预测提供验证和评价支持。