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Syo Yoshida, Ryohei Misumi, and Takeshi Maesaka


Cumulonimbus clouds, which cause local heavy rainfall and urban floods, can develop within 20 min after being detected by operational centimeter-wavelength (X-, C-, or S-band) weather radars. To detect such clouds with greater lead times, Ka-band radars at a wavelength of 8.6 mm together with operational X-band radars were used in this study. The vertically averaged radar reflectivity (VAR) of convective echoes detected by the Ka-band and X-band radars were defined as mesoscale cloud echoes (MCEs) and mesoscale precipitation echoes (MPEs), respectively. The time series of each echo was analyzed by an echo tracking algorithm. On average, MCEs that developed into MPEs (denoted as developed MCEs) were detected 17 min earlier than the MPEs and 33 min earlier than the peak time of the area-averaged VAR (VARa) for MPEs. Some MCEs dissipated without developing into MPEs (denoted as non-developed MCEs). There were statistically significant differences between the developed and non-developed MCEs in terms of the maximum VARa values, maximum MCEs areas, and increase amounts of the VARa values and MCE areas for the first 6–12 min after their detection. Among these indicators, the maximum VARa for the first 9 min showed the most significant differences. Therefore, an algorithm for predicting MCE development using this indicator is discussed.

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Ryohei Misumi, Hiroki Motoyoshi, Satoru Yamaguchi, Sento Nakai, Masaaki Ishizaka, and Yasushi Fujiyoshi


The liquid water fraction of individual snowflakes f is an important parameter when calculating the radar reflectivity of a melting layer. A ground-based observation of f at Nagaoka, Japan, was conducted by using dye-treated filter papers that were kept at a temperature of 0°C. From the results of these measurements, which consisted of 6179 particles taken with 44 sheets of filter paper, two empirical relationships are proposed. The first is a relationship between the ratio of liquid water flux to total precipitation intensity (F L; taking values from 0 to 1) and meteorological surface data. The second is a relationship to estimate f using the melted diameter of a snowflake, median mass diameter, and F L. It was determined that the root-mean-square errors for estimating F L and f by using these relationships were 0.160 and 0.144, respectively. It was also found that the ratio of raindrop flux to the total precipitation intensity F R was always below 0.1 when F L was less than 0.6 but increased rapidly when F L exceeded 0.8.

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Tsuyoshi Nakatani, Ryohei Misumi, Yoshinori Shoji, Kazuo Saito, Hiromu Seko, Naoko Seino, Shin-ichi Suzuki, Yukari Shusse, Takeshi Maesaka, and Hirofumi Sugawara
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Ryohei Misumi, Yoshinori Shoji, Kazuo Saito, Hiromu Seko, Naoko Seino, Shin-ichi Suzuki, Yukari Shusse, Kohin Hirano, Stéphane Bélair, V. Chandrasekar, Dong-In Lee, Augusto Jose Pereira Filho, Tsuyoshi Nakatani, and Masayuki Maki


The Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS) began as a Japanese domestic research project in 2010 and aimed to elucidate the mechanisms behind local high-impact weather (LHIW) in urban areas, to improve forecasting techniques for LHIW, and to provide high-resolution weather information to end-users (local governments, private companies, and the general public) through social experiments. Since 2013, the project has been expanded as an international Research and Development Project (RDP) of the World Weather Research Programme (WWRP) of the World Meteorological Organization (WMO). Through this project, the following results were obtained: 1) observation data for LHIW around Tokyo were recorded using a dense network of X-band radars, a C-band polarimetric radar, a Ku-band fast-scanning radar, coherent Doppler lidars, and the Global Navigation Satellite System; 2) quantitative precipitation estimation algorithms for X-band polarimetric radars have been developed as part of an international collaboration; 3) convection initiation by the interaction of sea breezes and urban impacts on the occurrence of heavy precipitation around Tokyo were elucidated by a dense observation network, high-resolution numerical simulations, and different urban surface models; 4) an “imminent” nowcast system based on the vertically integrated liquid water derived from the X-band polarimetric radar network has been developed; 5) assimilation methods for data from advanced observation instruments such as coherent Doppler lidars and polarimetric radars were developed; and 6) public use of high-resolution radar data were promoted through the social experiments.

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