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Investigation of added value at very high resolution with the Regional
Climate Model CCLM
Martin Suklitsch and Andreas Gobiet
Wegener Center for Climate and Global Change and Institute for Geophysics, Astrophysics and Meteorology, Institute of
Physics, University of Graz, Leechgasse 25, 8010 Graz, Austria (martin.suklitsch@uni-graz.at)
1. Introduction
Based on a large ensemble of sensitivity simulations at a
horizontal resolution of 10 km with the Regional Climate
Model CCLM (Will et al., submitted), merits and
shortcomings of this particular RCM have been
demonstrated (Suklitsch et al., 2008). In this study we
additionally deploy finer grids of 3 and 1 km horizontal
resolution for single month simulations in a winter and a
summer case in two test areas within the Alpine Region and
analyze the added value due to finer spatial resolution.
2. Method
In order to reach the very high horizontal resolution of 1km
a triple nesting approach is applied. Starting from ERA-40
(Uppala et al., 2001) lateral boundary data at roughly
120km horizontal grid spacing we first simulate the entire
Greater Alpine region at 10 km (red rectangle in fig. 1), then
the Eastern Alps (east of Innsbruck; green in fig. 1) at 3 km
and finally the two test regions at 1 km (blue): One hilly
region with relatively smooth orography, located in the
southeastern part of Styria, and a mountainous one, with
steep orography located in the “Hohe Tauern” region of the
Alps.
(1) There is a cold bias (area average in hilly region) at
any resolution. The cold bias ranges from −0.9K (July) to
−2.4K (January) at 10 km resolution, from −2.0K (July) to
−2.6K (January) at 3 km resolution, and amount to −1.8K
(July and January) at 1 km resolution. Qualitatively
similar results for one location in the Hohe Tauern region
are shown in figure 3, where the mean diurnal cycle of the
three resolution steps is compared to observation data.
(2) Precipitation (not shown) is overestimated at 10 and
3 km resolution, but underestimated at 1 km resolution.
The latter however strongly depends on the physical
parameterization: in case of the setup where graupel is
included in the microphysics scheme precipitation is
Figure 1. Domains used for this study. Red: 10 km,
green: 3 km and blue: 1 km horizontal resolution.
Dashed lines indicate extended domains, solid lines
the default ones.
3. First results
Figure 2 shows the 2m air temperature at each of the three
resolutions for the Hohe Tauern region. Here it is clearly
visible that the increased resolution yields more realistic
results. The value of the increased resolution will be
quantified using observational data of the Austrian Weather
Service (ZAMG), of the avalanche warning services of
Tyrol, Salzburg and Carinthia, and from the new high
resolution observation network WegenerNet (Kirchengast et
al., 2008).
A preliminary evaluation of the resolution chain (based on
selected examples) shows the following main features:
Figure 2. 2m air temperature for the “Hohe Tauern”
region in July 2007 as forecast by CCLM at 10, 3
and 1 km horizontal resolution (top to bottom).