Abstract
Aquaplanet experiments are used to investigate the physical convergence
of a Global Storm-Resolving model (GSRM) under successive, two-fold
horizontal grid spacing refinements from 160 km to 1.25 km. A
methodology based on the Richardson extrapolation method is used with
the aquaplanet hemispherical symmetry to quantify convergence. We use
the symmetrical and anti-symmetrical solution components to estimate the
asymptotic convergence pattern, the asymptotic estimate, and sampling
uncertainty. Based on successive refinements, different climate
statistics are explored to evaluate if they enter into a convergent
regime and, if so, what their convergent value is. Our analysis focuses
on global mean statistics related to the general circulation and aspects
that influence the climate: the meridional overturning circulation, the
tropical structure (the Inter-Tropical Convergence Zone (ITCZ), and the
zonal mean thermodynamic state), and the energy and water budget. Our
results show a kilometer and hectometer-scale horizontal grid spacing
requirement for physical convergence of the meridional overturning
circulation structure and global mean statistics. Distinctively, the
tropical structure is estimated to be very near their asymptotic values
at km-scale grid spacing, but the circulation intensity appears to
converge more slowly, as do the storm track and jet-stream. As we
increase the horizontal grid spacing, a better representation of clouds
and zonal distribution of water vapor drives convergence in the energy
and water budget. We conclude that simulations with a resolution of 2.5
km pose a great candidate for multi-decadal simulations within a
compromise of the meridional overturning circulation structure
convergence and intensity.