Lifecycle of anvil clouds in a warmer climate as seen by passive tracers in km-scale ICON simulations

Tropical anvil clouds exert a twofold impact on Earth’s radiation budget. The thickness of anvil clouds, and with it their radiative effects, change significantly throughout the cloud’s lifetime. Fresh anvils are initially thick, as the cloud ages and spreads out, the cloud loses mass. This leads to a rapid decrease in its cooling effect due to reflection of shortwave radiation until eventually the longwave warming effect dominates, resulting in a near neutral net radiative effect over the whole anvil lifecycle. However, our knowledge of anvil cloud lifetime and evolution in a warmer climate remains insufficient. A recent hypothesis suggests a thinning of anvil clouds in a warmer climate. However, it is currently not known whether this applies to all stages of the anvil lifecycle or only parts of it.

In this study, we aim to quantify changes in the cloud radiative effect of anvil cirrus across their lifecycle in a warmer climate. To this end, we use passive tracers implemented in the ICON model coupled to the one-moment aerosol module HAM-lite at 5 km resolution. This allows us to track the origin and evolution of individual anvils and to determine a time after detrainment. We run global 40-day simulations, a control present climate, and a warming simulation in which we increase the sea surface temperature by +4 K. We aim to detect changes in anvil lifecycle and thickness that modulate radiative effects. We hypothesize a disproportionate reduction in the thick, cooling phase of anvils relative to their thin warming phase, ultimately resulting in a net positive anvil radiative effect.