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Saito K.,JMA Meteorological Research Institute | Shimbori T.,JMA Meteorological Research Institute | Draxler R.,College Park
Journal of Environmental Radioactivity | Year: 2015

The World Meteorological Organization (WMO) convened a small technical task team of experts to produce a set of meteorological analyses to drive atmospheric transport, dispersion and deposition models (ATDMs) for the United Nations Scientific Committee on the Effects of Atomic Radiation's assessment of the Fukushima Daiichi Nuclear Power Plant (DNPP) accident. The Japan Meteorological Agency (JMA) collaborated with the WMO task team as the regional specialized meteorological center of the country where the accident occurred, and provided its operational 5-km resolution mesoscale (MESO) analysis and its 1-km resolution radar/rain gauge-analyzed precipitation (RAP) data. The JMA's mesoscale tracer transport model was modified to a regional ATDM for radionuclides (RATM), which included newly implemented algorithms for dry deposition, wet scavenging, and gravitational settling of radionuclide aerosol particles.Preliminary and revised calculations of the JMA-RATM were conducted according to the task team's protocol. Verification against Cesium 137 (137Cs) deposition measurements and observed air concentration time series showed that the performance of RATM with MESO data was significantly improved by the revisions to the model. The use of RAP data improved the 137Cs deposition pattern but not the time series of air concentrations at Tokai-mura compared with calculations just using the MESO data.Sensitivity tests of some of the more uncertain parameters were conducted to determine their impacts on ATDM calculations, and the dispersion and deposition of radionuclides on 15 March 2011, the period of some of the largest emissions and deposition to the land areas of Japan. The area with high deposition in the northwest of Fukushima DNPP and the hotspot in the central part of Fukushima prefecture were primarily formed by wet scavenging influenced by the orographic effect of the mountainous area in the west of the Fukushima prefecture. © 2014 The Authors.


Kobayashi T.,JMA Meteorological Research Institute | Masuda K.,JMA Meteorological Research Institute | Yamauchi H.,JMA Meteorological Research Institute | Adachi A.,JMA Meteorological Research Institute
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

A radar is a powerful tool for measurement of the 3-D structure of precipitation. Recently, polarimetric radar is widely used because it can measure the size of raindrops to some degree and therefore can measures more accurate rainfall rate than the conventional weather radar. A space-borne radar is also widely used in precipitation studies. The Tropical Rainfall Measuring Mission (TRMM) satellite has been continuously monitoring precipitation on a global scale since the launch in November, 1977. Following the TRMM, the Global Precipitation Mission (GPM) is scheduled to launch in 2013. The polarimetric parameters observed with the polarimetric radar depend on various precipitation properties in a complex way. Multiple scattering contributions cannot be neglected for a radar operated at higher frequency of 35 GHz higher onboard the GPM. To develop a robust algorithm for more accurate measurements of precipitation from those radars, we should evaluate how micro-physical properties of precipitation link to the received signals. We have developed a generalized radar simulator for polarimetric and space-borne radar (GPASS). This is a physically-based simulator in which the scattering properties of cloud and raindrops are calculated by using radio wave scattering theory. Thus we can make detailed study how the radar signals vary with micro-physical properties of precipitation by using the simulator. We will present the simulator in detail and the limit of the Rayleigh approximation for polarimetric radar. © 2011 SPIE.


Adachi A.,JMA Meteorological Research Institute | Kobayashi T.,JMA Meteorological Research Institute | Yamauchi H.,JMA Meteorological Research Institute | Onogi S.,JMA Meteorological Research Institute
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

Recent studies have shown that polarimetric radars are capable of providing distributions of rain intensity with high accuracy. Variables obtained by the polarimetric radars include radar reflectivity factor (Zhh), differential propagation phase (Φdp) and differential reflectivity (Zdr). A number of methods to estimate rain intensity from these variables have been proposed. In this study, the rain intensity estimated from the differential reflectivity and radar reflectivity factor measured with a C-band polarimetric radar is used to analyze a local heavy rainfall event as a case study because the differential reflectivity measured with C-band radar is more sensitive to large raindrops associated with heavy rainfalls than is radars operating at other frequencies. Results show that the estimated rainfall intensity agrees well with surface observations made during the event. Moreover, the so-called high Zdr column, a large differential reflectivity region was clearly analyzed aloft about 10 minutes prior to the local heavy rainfall on the ground, suggesting that the differential reflectivity observed with C-band polarimetric radar can be a good index to detect heavy precipitation events in advance. © 2011 SPIE.

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