“Spin-up” is time needed for a model’s result to become effectively free of influence from initial conditions, and it is usually excluded from analysis. Here, spin-up is examined by comparing one decadal simulation to another initialized 20 years prior, in order to determine when their solutions converge. Differences lessen over the first fall and winter, but re-emerge over the following spring and summer, suggesting that at least 1 annual cycle is needed to spin up regional climate simulations.

We examined the two-moment cloud microphysics sedimentation schemes of the ICON (ICOsahedral Nonhydrostatic) weather model, comparing the default semi-implicit with an explicit method faster on graphics processing units. Using idealized setups and thunderstorm case studies, we find differences in numerical diffusion and extreme precipitation rates due to changed coupling with the remaining microphysics. Neither method develops alarming instabilities in full model setups; both can be safely used.