Adjusting Timings for “Superparameterized” Climate Model Atmosphere Simulations
Superparameterized models are a new type of atmospheric model used in climate models that capture detailed cloud behavior by embedding a high-resolution cloud-resolving model (CRM) within a climate model gridbox. Superparameterized general circulation models (GCM) are in their infancy, have never been carefully tuned, and are incompletely understood especially in terms of the mechanisms that allow attractive forms of emergent behavior linked to organized deep convection. A recent Department of Energy-supported study explores the effect of reducing the large-scale model time step, which has the byproduct of increasing the frequency with which the planetary versus cloud resolving scales are allowed to interact. The experiments reveal interesting reductions in cloud biases, and a mysterious shift to a climate that has more bottom-heavy tropical convection, stronger rainfall extremes, and more faithfully satisfies the weak-temperature gradient. These results are relevant to understanding convective organization physics and informing climate model development in the next generation of convection-permitting GCMs.
Yu, S., and M. Pritchard. 2015. “The Effect of Large-Scale Model Time Step and Multiscale Coupling Frequency on Cloud Climatology, Vertical Structure, and Rainfall Extremes in a Superparameterized GCM,” Journal of Advances in Modeling Earth Systems 7(4), 1977–96. DOI: 10.1002/2015MS000493.