Differentiated Cloud-Radiation Characteristics over East Asian Subtropical and Tropical Regions Revealed by CMIP6 Models

Pronounced climatic differences occur over subtropical South China (SC) and tropical South China Sea (SCS) and understanding the key cloud-radiation characteristics is essential to simulating East Asian climate. This study investigated cloud fractions and cloud radiative effects (CREs) over SC and SCS simulated by CMIP6 atmospheric models. Remarkable differences in cloud-radiation characteristics appeared over these two regions. In observations, considerable amounts of low-middle level clouds and cloud radiative cooling effect appeared over SC. In contrast, high clouds prevailed over SCS, where longwave and shortwave CREs offset each other, resulting in a weaker net cloud radiative effect (NCRE). The models underestimated NCRE over SC mainly due to weaker shortwave CRE and less cloud fractions. Conversely, most models overestimated NCRE over SCS because of stronger shortwave CRE and weaker longwave CRE. Regional CREs were closely linked to their dominant cloud fractions. Both observations and simulations showed a negative spatial correlation between total (low) cloud fraction and shortwave CRE over SC, especially in winter, and exhibited a positive correlation between high cloud fraction and longwave CRE over these two regions. Compared with SCS, most models overestimated the spatial correlation between low (high) cloud fraction and SWCRE (LWCRE) over SC, with larger bias ranges among models, indicating the exaggerated cloud radiative cooling (warming) effect caused by low (high) clouds. Moreover, most models struggled to describe regional ascent and its connection with CREs over SC while they can better reproduce these connections over SCS. This study further suggests that reasonable circulation conditions are crucial to simulating well cloud-radiation characteristics over the East Asian regions.