Observed Cloud Type-Sorted Cloud Property and Radiative Flux Changes With the Degree of Convective Aggregation From CERES Data

Abstract

Cloud-radiation interactions are a critical mechanism for convective self-aggregation, especially the longwave radiative cooling of low clouds and environments. In this study, two data products from CERES observations combined with MERRA-2 reanalysis are used to understand the changes of cloud properties and radiative fluxes by cloud type with the degree of convective aggregation at the 1000-km scale, which is represented by the number of cloud objects (N), simple convective aggregation index (SCAI), modified SCAI (MCAI) or convective organization potential (COP). The changes with SCAI are similar to those with N as an index, agreeing with previous studies using grid-averaged properties. For changes from weak to strong degrees of aggregation using N and SCAI, area fractions of middle- and high-level cloud types decrease by up to 4% but those of low-level cloud types increase by up to 2%, and more infrared radiation is emitted to space (2–8 W m⁻²) from optically thin cloud types but more solar radiation is reflected (2–4 W m⁻²) from optically-thick cloud types. However, using COP (MCAI to lesser extent), area fractions of optically-thick cloud types increase, which emit less infrared radiation and reflect more solar radiation, whereas the area fractions of low-level clouds decrease. These results can be explained by greater expansion of cloud object sizes for COP than MCAI/SCAI as the degree of convective aggregation increases, which also explains the difference between SCAI and MCAI pertaining to the opposite changes of optically-thick high-level clouds. These results can have implications for understanding convective self-aggregation.