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Is the position of the model domain over the target area related to the
results of a regional climate model?
Kevin Sieck, Philip Lorenz and Daniela Jacob
Max Planck Institute for Meteorology, Hamburg, Germany, kevin.sieck@zmaw.de
1. Introduction
Most studies to investigate uncertainties in regional climate
modelling concentrated on the influence of domain sizes
(e.g. Laprise et al., 2008), treatment of the lateral boundary
conditions (e.g. Lorenz & Jacob, 2005) and uncertainties due
to different lateral forcings (PRUDENCE, ENSEMBLES).
However, the decision on the position of the model domain
over a certain target area was not in the focus of the
community. By now it is mainly done by experience and
subjective decisions. This study shows that results of a
regional climate model can depend on the position of the
model domain.
2. Experimental setup
All simulations were performed with the regional climate
model REMO (Jacob et al., 2007) at a horizontal resolution
of 0.5° (~55 km) over Europe with a domain-size of 81x91
gridboxes. The forcing at the lateral boundaries came from
the ERA-15 reanalysis dataset and ECHAM5/MPIOM
(Roeckner et al., 2003) simulations of the 20th century. The
integration periods for the first forcing were 10 years (1979-
1988) and for the latter 20 years (1950-1969). Several
members with slight shifts up to 2 gridboxes around a
centred control domain were integrated for both forcings.
3. Results
Results from the ERA-15 driven runs show that shifts of
the model domain by one gridbox lead to a systamatic
cooling or warming of the near surface temperatures
compared to the control domain depending on the
direction of the shift. Eastward shifts result in a warming
whereas westward shifts show a cooling in central Europe
up to 0.2 K between 1979 and 1988. This effect is even
stronger if the model domain is shifted by two gridboxes
(see Figure 1). Connected to this cooling is an anomalous
low pressure system located over the Czech Republic.
To determine if this is a feature of the regional model
ECHAM5/MPIOM forcing was used to run REMO.
Results show that no systematic variations appear when
shifting the model by two gridboxes.
4. Conclusions
The anomalous temperature and pressure patterns found in
the ERA-15 driven runs seem to be dependent on the
forcing that is used, because they are not showing up in
ECHAM5/MPIOM forced integrations. Nevertheless, for
ERA-15 forcing this feature seems to be quite robust.
5. Further studies
Further analysis on weather type frequencies for the
different runs can show if ERA-15 forcing tends to give
the regional model more freedom in developing mesoscale
features, so that a small shift in the model domain can lead
to significant differences in the climate due to internal
variability.
References
Jacob, D., Barring, L., Christensen, O. B., Christensen, J.
H., de Castro, M., Deque, M., Giorgi, F., Hagemann,
S., Lenderink, G., Rockel, B., Sanchez, E., Schar, C.,
Seneviratne, S. I., Somot, S., van Ulden, A., van den
Hurk, B. & UL, An inter-comparison of regional
climate models for Europe: model performance in
present-day climate, Climatic Change, 81, 31-52, 2007
Laprise, R., R. de Elia, D. Caya1, S. Biner, P. Lucas-
Picher, E. Diaconescu, M. Leduc, A. Alexandru, L.
Separovic, Challenging some tenets of regional
climate modelling, Meteorol Atmos Phys, 100, 3-22,
2008
Figure 1. Temperature difference in [K] between two
ERA-15 driven runs. Shown is the difference between
a run where the model domain was shifted two gridboxes
to the west and the control domain for the
period 1979-1988.
Lorenz, P. & D. Jacob, Influence of regional scale
information on the global circulation: A two-way
nesting climate simulation, Geophysical Research
Letters, 32, L18706, 2005
Roeckner, E., Bäuml, G., Bonaventura, L., Brokopf, R.,
Esch, M., Giorgetta, M., Hagemann, S., Kirchner, I.,
Kornblueh, L., Manzini, E., Rhodin, A., Schlese, U.,
Schulzweida, U. & Tompkins, A., The atmospheric
general circulation model ECHAM5: Model
description, Max Planck Institute for Meteorology,
Hamburg, Report Nr. 349, 127pp., 2003