Polarimetric Radar Observation of the Melting Layer in a Winter Precipitation System Associated with a South-Coast Cyclone in Japan

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  • SHUSSE Yukari
    National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan
  • MAESAKA Takeshi
    National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan
  • KIEDA Kaori
    National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan
  • IWANAMI Koyuru
    National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan

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Abstract

<p> In this study, we describe the spatial distribution of the melting layer (ML) in a winter stratiform precipitation system associated with a south-coast cyclone (SCC) on 30 January 2015 over the Kanto Plain, Japan, using an X-band polarimetric radar at Funabashi operated by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT). The detailed horizontal distribution of surface precipitation types based on weather reports from citizens provided by Weathernews Inc. (WNI reports) was also investigated in relation to the ML structure.</p><p> Surface precipitation in the Kanto region started with rain and then changed to snow around Tokyo. According to WNI reports, a large dry snow area formed around Tokyo by 0900 Japan Standard Time (JST; UTC + 9 hours), whereas surface rainfall continued in the southeast of the Kanto Plain (most of Chiba and the southern part of Kanagawa). A boundary line between the surface dry snow and rain areas became clear in the eastern part of Kanagawa and the northwestern part of Chiba. This boundary then gradually moved inland.</p><p> Polarimetric ML signatures suggesting the presence of melting snow were continuously observed above the rainfall area in the southeast of the Kanto Plain. The polarimetric ML signatures, on the other hand, approached the ground near the surface dry snow–rain boundary while the surface snowfall was predominant around Tokyo. During the mature snowfall period around Tokyo, the ML vertically extended below 1 km above sea level (ASL) near the surface dry snow–rain boundary, which indicates the presence of a local horizontal temperature gradient and a surrounding ∼ 0°C near-isothermal layer. It is suggested that this vertically extending ML coincided with the edge of a cold air mass in the lower atmosphere, which often forms during snowfall associated with SCCs in the Kanto region.</p>

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