Abstract
A common goal of next-generation Global Circulation Models (GCMs) is
that they should be “scale-aware”, which typically implies that such
models should not be excessively sensitive to grid spacings, and that
they should in some sense converge monotonically towards a result as
grid spacings decrease. While both horizontal and vertical resolution
have been treated in this manner, time resolution is typically viewed
differently. Specifically, a decrease in time step size is often viewed
as a “necessary evil”, being decreased only in cases where spatial
resolution is also decreased, requiring a change to the time resolution
to satisfy a CFL condition. Our experiments with the E3SM Atmosphere
Model suggest that cloud physics and precipitation in GCMs is in fact
quite sensitive to process coupling time step size, and that the biases
affected by time integration error are independent from (and of
comparable size to) biases due to other common sources of error, such as
grid spacing and choice of sub-grid-scale physics parameterizations.
This suggests that process coupling frequency is a key feature that
should be adjusted for future models.