大气粒子散射相函数的参数化方案比较及其改进

大气粒子散射相函数的参数化是大气辐射传输参数化的重要组成部分。文中全面比较了大气粒子的HenyeyGreenstein(HG)方案和双Henyey-Greenstein(DHG)方案,并在四流球谐函数展开累加法中,应用这两种相函数参数化方案计算气溶胶、云、霾粒子的反射率、透射率或吸收率。该研究结果表明:HG方案无法表现相函数的后向峰值,因而其计算的大气粒子反射率和透射率精度较差;DHG方案能较好地表征相函数的整体特征,但是该方案计算的相函数易出现后向异常峰值或为负值,并导致计算得到的气溶胶、云、霾粒子的反射率和透射率精度甚至会低于HG方案。对DHG方案进行进一步研究,提出了改进的DHG方案(MDHG)。MDHG方案计算结果稳定,并能很好表征相函数的前向和后向峰值的特征,其计算的大气粒子的反射率和透射率精度也较高。因此,MDHG方案是一种理想的相函数参数化方案。

Comparisons and improvement of parameterization schemes for the scattering phase function of atmospheric particles

The parameterization of the scattering phase function of atmospheric particles is an important part of the radiative transfer parameterization. The accuracy of Henyey-Greenstein (HG) scheme and Double Henyey-Greenstein (DHG) scheme are examined systematically. These two schemes are applied in the four-stream spherical harmonic expansion adding method to calculate the reflection/transmission/absorption of aerosols, clouds and haze particles. Results show that the HG scheme cannot realistically describe the backscattering pattern of the phase function, thereby reducing the accuracy of the calculated reflection and transmission of atmospheric particles.The peak of forward scattering and backscattering can be well represented by the DHG scheme in some cases. However, the DHG scheme often leads to abnormal backscattering peak or negative values of the phase function, which is unrealistic. In this case, the accuracy of reflection and transmission calculated by the DHG scheme are lower than those by the HG scheme.For this reason, a modified DHG scheme (MDHG) is proposed in this study to improve the phase function parameterization.The modified scheme is stable, and the traits of forward scattering and backscattering are well characterized.In addition, errors of reflection and transmission calculated by the improved scheme are smaller. Results of the study indicate that the MDHG scheme is appropriate for parameterizing the phase function.