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Projection of the Changes in the Future Extremes over Japan Using a
Cloud-Resolving Model (JMA-NHM) : Model Verification and First Results
Masuo Nakano, S. Kanada, M. Nakamura, S. Hayashi, T. kato, H. Sasaki, T. Uchiyama, K. Aranami,
Y. Honda, K. Kurihara and A. Kitoh
Advanced Earth Science & Technology Organization (AESTO) / Meteorological Research Institute (MRI), 1-1 Nagamine,
Tsukuba, Ibaraki, 305-0052, JAPAN; mnakano@mri-jma.go.jp
1. Introduction
Some extreme weather phenomena occur every year around
Japan in the warm season (from June to October). For
example, mesoscale convective systems around the Baiu
frontal zone often bring heavy rainfall over the Japan
islands. Typhoons also cause wind and flood damage. We
also experience drought or extremely high temperature in
the summer season. The changes in these extreme weather
phenomena in the future climate are great concerns. Due to
complex topography in the Japan islands, a super-high
resolution model is desired to represent extreme phenomena.
The Ministry of Education, Culture, Sports, Science and
Technology (MEXT) has launched a 5-year (FY2007-2011)
program, called as KAKUSHIN program, to contribute to
IPCC AR5. Under the framework of KAKUSHIN program,
our team is conducting global climate projection using a 20
km-mesh AGCM (AGCM-20km) and regional climate
projection in the vicinity of Japan using a 5 or 2 km-mesh
non-hydrostatic model (JMA-NHM). This paper focused on
the verification and first results of 5 km-mesh JMA-NHM
(NHM-5km).
2. Model
The model utilized in this study is JMA-NHM (Saito et al.
2006, 2007), which is developed at Meteorological Research
Institute (MRI) and Japan Meteorological Agency (JMA).
The horizontal resolution of JMA-NHM is set to be 5 km
(NHM-5km). The model domain is shown in Figure 1. In
NHM-5km, terrain-following vertical coordinate z* is
employed. The vertical grid in NHM-5km contains 50 levels
with variable grid intervals of 40 m (near surface) to 886 m
(model top). The model top is located at a 21.8 km height.
The Kain-Fritsch cumulus parameterization scheme and
improved Mellor-Yamada level 3 turbulence scheme
proposed by Nakanishi and Niino (2004) are utilized in
NHM-5km. The spectral boundary coupling (SBC) method,
developed at MRI by Kida et al. (1991) and implemented in
the JMA-NHM by Yasunaga et al. (2005), is employed in
NHM-5km simulations to reduce phase errors between the
outer model and NHM-5km.
Figure 1. NHM-5km domain and topography
3. Experimental Design
Since our targets are extreme phenomena from June to
Octorber, NHM-5km is initialized at 00UTC 17 May
every experiment year, and the time integrations are
performed until 00UTC 1 November.
First, in order to validate the accuracy of NHM-5km
simulations, perfect boundary experiments are conducted
using initial and boundary conditions produced from the
JMA operational regional analysis data (RANAL), which
have a horizontal resolution of 20 km. The experiments
are performed for 5 warm seasons from 2002 to 2006.
Second, NHM-5km is nested within the simulations of
AGCM-20km (TL959L60; Mizuta et al., 2006)
experiments in the present (1990-1999) and future (2086-
2095) climates. In the AGCM-20km experiment for
present climate, observed SST and sea ice distribution are
utilized as bottom boundary conditions. On the other hand,
for future climate experiments, averaged SST/sea ice
increment and trend predicted by CMIP3 models are
added to detrended observed SST and sea ice distribution.
More detail can be found in Mizuta et al. (2008). The
SRES-A1B emission scenario is used in this study.
4. Perfect boundary experiments
The results of perfect boundary experiments are verified
using observed precipitation and temperature data by
Automated Meteorological Data Acquisition System
(AMeDAS) of the JMA. The AMeDAS has about 1300
rain gauges over Japan (horizontal resolution of
approximately 17 km) and about 850 stations for
temperature, wind and sun shine duration observation over
the Japan islands (horizontal resolution of approximately
21 km).
The NHM-5km results show a good agreement with
observed monthly rainfall amount (e.g., Fig. 2).
Appearance frequency of simulated daily precipitation
amount exceeding 100 mm is slightly overestimated.
Simulated monthly mean temperature has warm bias of 1
K. The simulated number of maximum consecutive dry
days by NHM-5km also agrees with the observed one.
Fifty nine typhoons come into NHM-5km domain during
2002-2006. Track of typhoons and their accompanying
precipitation distribution and amount observed in Japan
are also simulated well.
5. Present Climate and Future projection
experiments
The NHM-5km results are compared with 1990s observed
rainfall and temperature data. Less monthly precipitation
amount in June (-22%) and more precipitation amount in
July (+20%) are simulated by NHM-5km. These gaps are
mainly brought from the poor reproducibility of the Baiu
front in the AGCM-20km. Less precipitation amount is
also simulated in September (-33%). This gap is mainly
brought from the underestimation of number of typhoon