TECHNICAL REPORTS OF THE METEOROLOGICAL RESEARCH INSTITUTE No.76 2015

A. Preface1
The 2011 off the Pacific coast of Tohoku Earthquake (Great East Japan Earthquake) andtsunami occurred on 11 March 2011 and caused severe damage in Japan. The United Nations
Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) was asked to produce ascientific report for the General Assembly on the levels and effects of radiation exposure causedby the accident at the Fukushima Daiichi Nuclear Power Plant, and UNSCEAR requested theWorld Meteorological Organization (WMO) to develop a set of meteorological analyses forassessing the atmospheric transport, dispersion, and deposition of radioactive materials. In
response to UNSCEAR’s request, the WMO’s Commission for Basic Systems convened atechnical task team of experts from five countries (Austria, Canada, Japan, United Kingdom,and the United States) in November 2011. The primary aim of this team was to examine how
the use of meteorological analyses could improve atmospheric transport, dispersion, anddeposition model (ATDM) calculations.
As the Regional Specialized Meteorological Center of the country in which the accident
occurred, the Japan Meteorological Agency (JMA) collaborated with the WMO Task Team byproviding its mesoscale analysis based on operational four-dimensional variational data
assimilation and radar/rain gauge-analyzed precipitation (RAP) data in the standard WMO
format (GRIB2). To evaluate the quality of the meteorological analyses, the WMO Task Team
conducted test simulations with their regional ATDMs and different meteorological analyses.
JMA developed a regional ATDM for radionuclides by modifying its operational regional
atmospheric transport model, which had been previously used for photochemical oxidant
predictions and volcanic ashfall forecasts. The modified model (hereafter referred to as JMARATM) newly implemented dry deposition, wet scavenging, and gravitational settling ofradionuclide aerosol particles. The preliminary and revised calculations of JMA-RATM wereconducted with a horizontal concentration and deposition grid resolution of 5 km and a unit
source emission rate, in accordance with the Task Team’s protocols.
This technical report describes JMA’s contribution to the WMO Task Team and summarizes
the Task Team activities and relevant ATDM modeling carried out at the MeteorologicalResearch Institute (MRI) of JMA.
The authors of this technical report thank many people for their help in making both ourparticipation in Task Team activities and this technical report possible. In particular, we are
grateful to Yoshiaki Takeuchi (then Director), Keiichi Katayama, Jun-ichi Ishida, and Yoshiaki
Sato of the Numerical Prediction Division of JMA, and Naoyuki Hasegawa, Takashi Yoshida,
Harutoshi Goda, and Tatsuya Kimura of the Planning Division of JMA, for their help with boththe Task Team activities and the preparation of this technical report. We also thank Masao1K. Saito1

TECHNICAL REPORTS OF THE METEOROLOGICAL RESEARCH INSTITUTE No.76 2015

Mikami, Tadashi Tsuyuki, Masaomi Nakamura, and staff of the Office of Planning of MRI for
their help during the production of this technical report. A report on the Task Team activities
in Japanese has been published in Sokko-jiho (Saito et al., 2014), the bulletin of JMA’s business
reports. Noboru Nemoto of the Numerical Prediction Division of JMA, Glenn Rolph of the U.S.
National Oceanic and Atmospheric Administration, and Masaru Kunii of MRI contributed
Sections C-3 and C-6, D-4, and G-4, respectively. A part of this study was supported by theMinistry of Education, Culture, Sports, Science and Technology through its High-Performance
Computing Infrastructure Strategic Program for Innovative Research (SPIRE) Field 3, “Ultrahigh Precision Meso-Scale Weather Prediction.”
The report is organized as follows. Section B presents an overview of the WMO Task Teamand the Task Team meetings. Section C reports on JMA’s contributions to the WMO Task
Team. The operational mesoscale analysis and RAP data, including a data conversion tool
prepared by JMA to facilitate their use by the scientific community, are described. In Section
D, the ATDM experiments conducted by the Task Team members are presented. Section E
describes the JMA-RATM and the modifications implemented to support the Task Team
activities. Experiments conducted to test the sensitivity of the JMA-RATM calculations to someof the ATDM parameters (release height, number of computational particles, wet scavenging
coefficient and application height, and dry deposition application height) are also described.
Section F introduces the ATDMs of each of the Task Team member countries, and the resultsof those ATDM calculations are presented and verified against 137Cs deposition measurements
and the air concentration time series. In Section G, relevant ATDM modeling conducted at MRI
and JMA is introduced, including an ATDM intercomparison performed by the Science Councilof Japan and an emission source estimation made by using an inverse model. A special
contribution from Prof. Toshiki Iwasaki of Tohoku University illustrates the necessity to utilize
ATDM modeling in the nuclear power plant accident. Section H is the list of references. Section
I, the appendix, contains copies of the WMO Task Team meeting reports, courtesy of the WMO.

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