Capturing and explaining the effects of three-dimensional radiative transfer on cloud evolution with the dynamic TenStream solver

Abstract. Radiative transfer is an inherently three-dimensional (3D) process that, for computational reasons, is still approximated as one-dimensional (1D) in most atmospheric models. To address this limitation, Maier et al. (2024) introduced the dynamic TenStream solver, which reduces the cost of 3D radiative transfer calculations through incomplete solves. Here, we investigate how coupling dynamic TenStream to the large-eddy simulation model PALM affects cloud development compared to simulations using conventional 1D and full 3D radiation. Results show that during daytime, clouds driven by either of the 3D solvers organize into cloud streets oriented perpendicular to the solar incidence angle, whereas with 1D radiation they remain more or less randomly distributed. Moreover, daytime clouds grow larger, become thicker, and contain more liquid water with 3D radiative transfer. It is shown that these differences arise because, unlike in the 1D case, clouds coupled to 3D radiation are not positioned directly above their own shadows. Instead, they are located over areas of enhanced net surface irradiance, where values even exceed those in the clear-sky columns of the 1D simulation, strengthening rather than weakening the associated updrafts. Additionally, 3D radiation is shown to reduce the domain-averaged net thermal emission at the surface, which affects the surface energy budget and is primarily balanced by an increase in the domain-averaged latent heat flux, resulting in a greater release of water vapor into the atmosphere. Both effects are captured by dynamic TenStream, demonstrating its ability to represent 3D radiative effects on cloud development at a substantially lower computational cost.