A Case Study of Cumulus Convection Over Land in Cloud‐Resolving Simulations With a Coupled Ray Tracer.

We present simulations of cumulus convection over land with shortwave radiation computed by a Monte Carlo ray tracer coupled to the flow solver. Ray tracing delivers very realistic in‐cloud heating rates and global horizontal irradiance fields. The necessary performance of the ray tracer has been enabled by the raw power of graphics processing unit computing and from techniques for accelerating data lookup and ray tracer convergence. We used a case study over a grassland in the Netherlands to compare simulations with a coupled ray tracer to those with a conventional two‐stream solver, and to test ray tracer convergence. We demonstrate that the simulated cloud evolution is insensitive to the convergence of the ray tracing across a wide range of samples per pixel per spectral quadrature point. Furthermore, simulations with a coupled ray tracer produce surface irradiance patterns that resemble observations and that strongly feed back to the evolution of clouds via locally enhanced surface heat fluxes. Plain Language Summary: Clouds absorb and reflect solar radiation and create spatial patterns at the land surface of cloud shadows interspersed with sunny regions. These patterns are currently largely simplified in most weather models because radiation computations cost a lot of computer power. We have developed a fast and realistic numerical radiation model that runs on a modern computer graphics card. By doing so, we can do simulations that produce radiation patterns that closely resemble reality and study how these patterns affect clouds. This enables us to improve our understanding of the complex interactions between clouds, solar radiation, and the Earth's surface. Key Points: We present graphics processing unit‐accelerated cloud‐resolving simulations with a coupled ray tracerSimulated cloud statistics are insensitive to ray tracer convergence across a wide range of sample sizesStrong coupling between surface irradiance patterns and cloud evolution underlines need for coupled 3D radiative transfer [ABSTRACT FROM AUTHOR]