Domain Nesting in ICON and its Application to AMIP Experiments with
Regional Refinement
Abstract
The domain nesting of the icosahedral non-hydrostatic (ICON) model has
been used operationally at Deutscher Wetterdienst for several years. Now
it was also made available for the atmospheric part of the ICON Earth
system model. With this new climate configuration, regionally higher
resolved simulations without the additional use of a separate regional
climate model (RCM) are possible. Simulations were performed for the
years 1979-2010 at a global resolution of about 80 km and a subdomain
over Europe at 40 km resolution. Two simulations with this setup were
evaluated and compared: one with a feedback from the regional subdomain
to the global domain (two-way nesting) and one without feedback (one-way
nesting). The mean atmospheric state of both simulations on the global
scale is only slightly different compared to a reference experiment.
However, comparisons to reanalyses show regionally distinct biases. The
feedback from the subdomain to the global domain has a similar impact
over Europe as a globally higher resolution, indicating a stronger
North-Atlantic Oscillation at higher horizontal resolution. Over Europe,
the skill is higher in the subdomain than in the global domain, but no
systematic advantages can be attributed to the feedback. Artifacts at
the lateral boundaries of the regional subdomain, as they are known from
RCM simulations, also occur strongly in the simulation without feedback
and are eliminated by allowing the feedback. A further reduction of
resolution dependency of model physics is supposed to improve
particularly the simulation with feedback.