Evaluation of the CMIP6 marine subtropical stratocumulus cloud albedo and its controlling factors

Bida Jian,Yuxin Zhao,Min Zhang,Jing Wang,Yarong Li,Jianping Huang,Guoyin Wang,Jiming Li

doi:10.5194/acp-21-9809-2021

Abstract

Abstract. The cloud albedo in the marine subtropical stratocumulus regions plays a key role in regulating the regional energy budget. Based on 12 years of monthly data from multiple satellite datasets, the long-term, monthly and seasonal cycle of averaged cloud albedo in five stratocumulus regions were investigated to intercompare the atmosphere-only simulations between phases 5 and 6 of the Coupled Model Intercomparison Project (AMIP5 and AMIP6). Statistical results showed that the long-term regressed cloud albedos were underestimated in most AMIP6 models compared with the satellite-driven cloud albedos, and the AMIP6 models produced a similar spread as AMIP5 over all regions. The monthly averaged values and seasonal cycle of cloud albedo of AMIP6 ensemble mean showed a better correlation with the satellite-driven observations than that of the AMIP5 ensemble mean. However, the AMIP6 model still failed to reproduce the values and amplitude in some regions. By employing the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) data, this study estimated the relative contributions of different aerosols and meteorological factors on the long-term variation of marine stratocumulus cloud albedo under different cloud liquid water path (LWP) conditions. The multiple regression models can explain ∼ 65 % of the changes in the cloud albedo. Under the monthly mean LWP ≤ 65 g m−2, dust and black carbon dominantly contributed to the changes in the cloud albedo, while dust and sulfur dioxide aerosol contributed the most under the condition of 65 g m−2 < LWP ≤ 120 g m−2. These results suggest that the parameterization of cloud–aerosol interactions is crucial for accurately simulating the cloud albedo in climate models.

Highlights

One of the critical parameters in regulating the distribution of solar radiation in the atmosphere and surface is cloud albedo, which is the proportion of incoming solar radiation reflected by clouds (Mueller et al, 2011; Wall et al, 2018)
As the values averaged over Aqua and Terra albedos and cloud fractions were used as the observations in this study, the regressed cloud albedo values need to be within the range of the Aqua and Terra values (Engström et al, 2014)
The cloud albedo in the marine subtropical stratocumulus regions has a key role in regulating the regional energy budget

Summary

Introduction

One of the critical parameters in regulating the distribution of solar radiation in the atmosphere and surface is cloud albedo, which is the proportion of incoming solar radiation reflected by clouds (Mueller et al, 2011; Wall et al, 2018). This study focused on the cloud albedo in the subtropical marine stratocumulus regions as it is difficult to reproduce the cloud properties by numerical models (Eyring et al, 2016), which results in a larger uncertainty in energy budget simulations and climate predictions (Wood, 2012). The subtropical marine stratocumulus regions are mainly covered by low-level clouds that usually reflect most of the solar radiation and significantly contribute to the planetary albedo (Seethala et al, 2015). The contribution of the cloud albedo to planetary albedo over these dark oceans could be tremendous compared with those over snow- or ice-covered regions with a high surface albedo (Mueller et al, 2011). It is a challenge to accurately estimate the cloud albedo in regions where there are different types of clouds for evaluating the cloud albedo resulting

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