Evaluation of Dynamical Downscaling in a Fully Coupled Regional Earth
System Model
Abstract
A set of decadal simulations has been completed and evaluated for gains
using the Regional Arctic System Model (RASM) to dynamically downscale
data from a global Earth system model (ESM) and two atmospheric
reanalyses. RASM is a fully coupled atmosphere - land - ocean - sea ice
regional Earth system model. Nudging to the forcing data is applied to
approximately the top half of the atmosphere. RASM simulations were also
completed with a modification to the atmospheric physics for evaluating
changes to the modeling system. The results show that for the top half
of the atmosphere, the RASM simulations follow closely to that of the
forcing data, regardless of the forcing data. The results for the lower
half of the atmosphere, as well as the surface, show a clustering of
atmospheric state and surface fluxes based on the modeling system. At
all levels of the atmosphere the imprint of the weather from the forcing
data is present as indicated in the pattern of the monthly and annual
means. Biases, in comparison to reanalyses, are evident in the ESM
forced simulations for the top half of the atmosphere but are not
present in the lower atmosphere. This suggests that bias correction is
not needed for fully-coupled dynamical downscaling simulations. While
the RASM simulations tended to go to the same mean state for the lower
atmosphere, there is a different evolution of the weather across the
ensemble of simulations. These differences in the weather result in
variances in the sea ice and oceanic states.