Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Recent Development of a Regional Air/Land Surface/Sea/Ice Coupling
Modeling System, “the RCAO Experience”
Markku Rummukainen
Rossby Centre, Swedish Meteorological and Hydrological Institute, SE-601 76 Norrköping, Sweden. E-mail:
Markku.Rummukainen@smhi.se
1. Regional modeling
Regional modeling is a tool in operational forecasting,
climate research and environmental studies. There are many
important synergies between regional and global modeling,
development of theory and observational studies. Likewise,
development and application of modeling are interlinked.
In the past, much has been learned about the different
components of the physical climate system, such as the
atmosphere, the land surface, the oceans, and the sea ice.
The push to address these as a coupled system is an ongoing
challenge and holds much promise as to improving our
understanding of the system and to developing better tools to
study it.
Coupled modeling is the norm in global climate modeling.
Important steps towards the same also in regional climate
modeling have been taken during the past few years. The
Rossby Centre Regional Atmosphere-Ocean Model, RCAO,
has been one of these advances. This presentation takes a
look into uses and possibilities of coupled regional
modeling, building especially on experiences from RCAO.
A near-term outlook is also given and some guidance is
suggested for future work.
2. RCAO
RCAO (Döscher et al. 2002) builds on the Rossby Centre
Regional Atmosphere Model, RCA (Rummukainen et al.
2001, Jones et al. 2004), and the 3-dimensional Rossby
Centre Regional Ocean Model, RCO (Meier et al. 2003). It
also includes a river routing routine based on a large-scale
application of the HBV hydrological model from Bergström
et al. (1973) and Lindström et al. (1997), and accounts for
lakes and lake systems following Ljungemyr et al. (1996)
and Omstedt (1999). The coupler software is based on
Valcke et al. (2000).
sea ice
ocean
∆t mod
atmosphere
rivers
land surface
∆t coup
OASIS
Figure 1. Schematics of the RCAO system, its main
components and their coupling.
Model development is a long-term activity at the Rossby
Centre. Model evaluation and utilization of observational
data is an inherent part of this. Process studies, climate
change projections and support to environmental, energy
and impact research is seen as an important application
and a natural follow-up of model development and
evaluation efforts.
3. The evaluation of RCAO
RCAO has been developed, evaluated and applied for
Northern Europe. Its components, especially RCA and
HBV, have been applied also on other regions. The latter
has improved model evaluation possibilities by widening
the range of conditions under which the model is tested,
and facilitated benefiting from special observational data
sets. It has also been shown, that the coupling exercise can
also lead to new insights to and important improvements
in model components that have been developed in
isolation. Coupling carries additional potential to expose
compensating errors and suchlike. Presently, RCAO is
being set up for the Arctic region, a process of which is
expected to improve the system also when applied in the
Baltic Sea region.
4. Outlook and recommendations
RCAO, as any other model, is a research and development
tool. As such, a model never becomes perfect, or replaces
the need to measure and to monitor. However, just as
much as measurements can provide us with information
that is not attainable by modeling, the latter can go where
measurements do not reach. Modeling and
measuring/monitoring are in this sense complementary,
and should be understood as such. We promote close
collaboration between these activities.
Among the future development and application of RCAO
are studies of the climate of the past (paleoclimate topics
and regional reanalyses for the 20 th Century), and climate
change projections for the 21 st Century. Another intention
is to keep improving the existing model system, but also to
increase its complexity along the lines envisioned in
global “Earth System Modeling”. Regional modeling has
an opportunity to do so with a degree of detail (resolution)
expected to become “typical” global modeling during the
coming years. Thus, development of regional modeling,
today, can contribute to improved global modeling to
come. Last but not least, we recognize the usefulness and
promise of synergy between operational, environmental
and climate modeling, and wish to promote increased links
between these, e.g. within the context of BALTEX.
References
Bergström, S. and Forsman, A. 1973. Development of a
conceptual deterministic rainfall-runoff model. Nord.
Hydrol., 4, 147-170.