Development of a Two-way Nested LETKF System for Cloud-resolving Model - Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications - page 497

has the merit that it can be executed with limited computational resources by cutting
out small regions from a whole domain. Some modifications, such as the no-cost
smoother that was used in producing the initial seeds and boundary conditions of
the inner LETKF, were also investigated. To apply this nested system to various
phenomena (e.g. synoptic fronts and typhoons), rainfall systems that extend wider
than the domain of the Inner LETKF should be investigated.
To increase the accuracy of rainfall forecast, the high-resolution data that pro-
vides small-scale disturbances is indispensable. The project “Tokyo Metropolitan
Area Convection Study for Extreme Weather Resilient Cities (TOMACS)” in which
local heavy rainfalls developed in the Tokyo Metropolitan area were observed by
Ku-band radar, surface dense network and Doppler lidars etc. was started in 2011.
The observation data of TOMACS will be used as assimilation data of the nested
LETKF system.
Because of the 'Tohoku-earthquake' that occurred over Eastern Japan on 11th
March 2011, computer resources were limited so the number of ensemble members
and the horizontal grid of LETKFs became 12 and .However,

results of this study show the potential of the nested LETKF system. The results
shown in this study will be further investigated using the high-performance super
computer'Kei', which will be provided by the 'High Performance Computing
Infrastructure' project.

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Acknowledgements The authors would like to express their gratitude to Dr. Yoshinori Shoji
of Meteorological Research Institute, Dr. Tadashi Fujita of Numerical Prediction Division/JMA,
Mr. Yuji Esaki of Osaka District Meteorological Observatory and anonymous reviewers, who
provided the PWV and SWV data and their useful comments. The authors' gratitude extends to the
Geospatial Information Authority of Japan and the Osaka District Meteorological Observatory of
JMA, which provided the GPS data and Doppler radar data. The improvements of severe weather
forecasts (i.e. local heavy rainfalls), which were achieved by the assimilations of Doppler radar
data, will contribute to aviation safety and the mitigation of damages of other urban functions.
The “Kasaneru 3D tool” developed by Tokyo District Meteorological Observatory of JMA was
used to generate the rainfall distribution graphics observed by the operational radars and the
surface meteorological data distribution graphics. This study was performed by the “Studies on
formation process of line-shaped rainfall systems and predictability of rainfall intensity and moving
speed” and the “Study of advanced data assimilation and cloud resolving ensemble technique for
prediction of local heavy rainfall” projects.

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