On the sensitivity of aerosol-cloud interactions to changes in sea surface temperature in radiative-convective equilibrium

Abstract. Clouds play a crucial role in regulating Earth's energy balance and are influenced by anthropogenic aerosol concentration (N_a) and sea surface temperature (SST) changes. However, these two factors – aerosols and SST – are typically studied independently. In this study, we employ idealized cloud-resolving, radiative-convective-equilibrium simulations to explore aerosol-cloud interactions (ACI) under different SSTs. Our findings reveal that ACIs are dependent on the prescribed SST, even at equilibrium conditions. Specifically, we show that increasing N_a leads to a decline in top-of-atmosphere (TOA) energy gain across SSTs due to changes in the cloud radiative effect, both in the short-wave and the long-wave parts of the spectrum. TOA short-wave flux changes with an increase in N_a are found to be more sensitive to the underlined SST conditions compared to long-wave radiation. The variations in how the clouds' short-wave radiative effect responds to N_a at various SSTs are explained by variations in the sensitivity of the water content in the cloud. Specifically, the sensitivity of the water content to N_a decreases with SST due to deepening of the warm, liquid portion of the cloud. This deepening results in clouds that are less responsive to aerosol-induced warm rain suppression. Furthermore, with an increase in N_a, we observe an increase in latent heat release at the upper troposphere associated with heightened production of snow and graupel. We show that this trend, which is consistent across all SSTs, affects the anvil cloud cover by affecting the static–stability at the upper troposphere via a similar mechanism to the iris–stability effect, resulting in a decline in TOA long-wave energy gain. In conclusion, under the ongoing climate change, studying the sensitivity of clouds to aerosols and SST should be conducted concomitantly as mutual effects are expected.