Observational evidence for a modulation of the tropical radiation budget by deep convective aggregation

Abstract:

Idealized modelling studies have suggested that the spatial distribution of deep convection, especially the degree of clustering of deep clouds, could impact humidity, cloud coverage and the Earth's radiation balance. We will show that satellite observations support these modelling inferences: on average over the tropical belt, when deep convection is more aggregated at the mesoscale, the free troposphere is drier, the deep-convective cloud coverage is less extensive, and the emission of heat to space is increased. But how important is the role of convective aggregation in the modulation of the tropical radiation budget compared to other factors? For instance, the lower-tropospheric stability is known to be another strong modulator of the radiation budget through its influence on marine low clouds and thus the reflection of solar radiation. We will show that over the period 2001-2017, the contributions of deep convective aggregation and lower-tropospheric stability to the monthly modulation of the tropical radiation budget are complementary, largely independent of each other, and equally strong. The implications of these observational findings for climate change and for climate modelling will be discussed.