In this study, we find significant sensitivity to the choice of time
step for the Energy Exascale Earth System Model's atmospheric component,
leading to large decreases in the magnitude of cloud forcing when the
time step is reduced to 10 seconds. Reducing the time step size for the
microphysics increases precipitation, leading to a drying of the
atmosphere and an increase in surface evaporation. This effect is
amplified when the microphysics is substepped together with other cloud
physics processes. Coupling the model's dynamics and physics more
frequently reduces cloud fraction at lower altitudes, while producing
more cloud liquid at higher altitudes. Reducing the deep convection time
step also reduces low cloud mass and cloud fraction. Together, these
results suggest that cloud physics in a global circulation model can
depend strongly on time step, and in particular on the frequency with
which cloud-related processes are coupled with each other and with the
model dynamics.