2007 Annual Report - jamstec japan agency for marine-earth ...

the precipitation is simulated well Figu.6e.
These results suggest that the change in the precipitation is
more strongly controlled by the change in the long-term variation
of large scale atmospheric circulation than by the change in
daily variations of precipitation process.
The PCS run can be also applied to future projections. The
PCS run would reduce the uncertainty caused by the natural
variability in the simulated climatic change and exclude model
biases in the present climatology reproduced by each GCM.
The PCS run would contribute to the reduction of the uncertainty
of the downscaling method. The reproducibility of the climate
change was confirmed by the PCS run in this study, which
contributes to project the future regional climate.
about 20km 20km-AGCM, precipitation is produced by the
convective parameterization and large-scale condensation.
To investigate degree of risk of hydrological disasters, the
mean precipitation amount among three heavy precipitation
events that ranked the highest every year P Top3 at each grid
point was used as an index of extreme precipitation. Figure7
shows distributions of P Top3 for the accumulation periods of 1, 6,
and 48 hours with 20km-AGCM, 5km-NHM, and observation.
The P Top3 for shorter accumulation periods is useful index in
association with short-span heavy precipitation induced by
cumulonimbus clouds. Steep mountains and densely populated
areas enhance the significance of short-span heavy precipitation
indices in Japan. The P Top3 for longer accumulation periods is
associated with mesoscale precipitation systems and maximum
flow for larger rivers.
The P Top3 with 20km-AGCM and 5km-NHM were underestimated
in comparison with the observation. However, P Top3
with 5km-NHM was reproduced significantly better than that
with 20km-AGCM, especially for the shorter accumulation
periods. The difference of P Top3 for the longer accumulation
periods between these models was small. For the estimation of
extreme precipitation for shorter accumulation periods, nonhydrostatic
model with finer resolution is considered to be
Fig.6 Distributions of ten-year mean monthly precipitation unit:
mm month-1 in June: a observations at the stations and c
simulation by the Hindcast run in the 1990s. Differences in precipitation
between the 1960s and the 1990s b observed at the stations, d
simulated by the Hindcast run, and e simulated by the PCS run. In
Figs. 6b, 6d, and 6e, blue red shading indicates that precipitation
increased decreased from the 1960s to the 1990s. Kawase et al,
2008 submitted to SOLA.
required.
One of the most noticeable and interesting changes in precipitation
over the land areas of Japan projected by 5km-NHM
was enhancement of precipitation in the mountainous areas
along the Pacific coast of western Japan not shown. This
enhancement is considered to result in incremental low-pressure
induced by the enhancement of moist diabatic heating around
c. Cloud/Precipitation Process Group
Kyushu in which precipitation and updraft was originally large.
c-1.Reproducibility evaluation of extreme precipitation in the
Baiu season using a cloud-system-resolving model
The reproducibility of extreme precipitation in the Baiu
season around Japan was evaluated using a non-hydrostatic
cloud-system-resolving regional atmospheric model with a horizontal
grid size of 5km 5km-NHM. Precipitation is explicitly
produced by cloud physics schemes with bulk parameterization.
For the outer condition of 5km-NHM, which is an atmospheric
general circulation model with a horizontal grid size of