LASG Global AGCM with a Two-moment Cloud Microphysics Scheme: Energy Balance and Cloud Radiative Forcing Characteristics

Abstract

Cloud dominates influence factors of atmospheric radiation, while aerosol-cloud interactions are of vital importance in its spatiotemporal distribution. In this study, a two-moment (mass and number) cloud microphysics scheme, which significantly improved the treatment of the coupled processes of aerosols and clouds, was incorporated into version 1.1 of the IAP/LASG global Finite-volume Atmospheric Model (FAMIL1.1). For illustrative purposes, the characteristics of the energy balance and cloud radiative forcing (CRF) in an AMIP-type simulation with prescribed aerosols were compared with those in observational/reanalysis data. Even within the constraints of the prescribed aerosol mass, the model simulated global mean energy balance at the top of the atmosphere (TOA) and at the Earth’s surface, as well as their seasonal variation, are in good agreement with the observational data. The maximum deviation terms lie in the surface downwelling longwave radiation and surface latent heat flux, which are 3.5 W m^-2 (1%) and 3 W m^-2 (3.5%), individually. The spatial correlations of the annual TOA net radiation flux and the net CRF between simulation and observation were around 0.97 and 0.90, respectively. A major weakness is that FAMIL1.1 predicts more liquid water content and less ice water content over most oceans. Detailed comparisons are presented for a number of regions, with a focus on the Asian monsoon region (AMR). The results indicate that FAMIL1.1 well reproduces the summer-winter contrast for both the geographical distribution of the longwave CRF and shortwave CRF over the AMR. Finally, the model bias and possible solutions, as well as further works to develop FAMIL1.1 are discussed.

摘要

云是影响大气辐射的主要因子之一, 气溶胶-云相互作用则对云的时空分布具有十分重要的影响. 为了提高大气物理研究所LASG实验室大气环流模式(FAMIL)对气溶胶-云相互作用的模拟能力, 一个基于物理过程的双参数云微物理参数化方案(CLR2)被引入到该模式中, 该参数化方案能够更合理地刻画气溶胶-云相互作用过程, 新的模式被命名为FAMIL1.1. 为了评估新模式的模拟性能, 我们首先将模式模拟的能量收支和云辐射强迫特征与再分析资料和观测资料进行了对比分析. 结果表明, 即使使用预设的气溶胶质量浓度, 新模式也能够合理模拟出大气层顶和地表全球平均的能量收支及其季节循环特征. 最大偏差项为到达地表的长波辐射和地表的潜热通量, 偏差分别为3.5 W m⁻²(相对偏差为1%)和3 W m⁻²(相对偏差为3.5%). 模式也能够合理地再现全球大气层顶的净辐射通量和净云辐射强迫的空间分布特征, 与观测结果的空间相关系数可分别达到0.97和0.9. 模式的主要偏差在于对液态云水含量的高估和冰水含量的低估. 此外, 我们也关注模式的区域模拟偏差, 并聚焦于东亚季风区. 结果表明, 新模式能够合理的再现东亚季风区云辐射强迫的空间分布特征以及其显著的冬-夏差异. 文末对模式的偏差和可能的改进方法、以及下一步的研发计划进行了相关讨论.