ALBERT

Beschreibung: The coastal areas in Japan that face the Sea of Japan is exposed to the cold and dry winter northwesterly monsoon. This air flow obtains large amount of moisture from the relatively warm Sea of Japan, resulting in enormous snowfall and snow water equivalent (SWE) especially in the mountainous region. However, reliable quantitative information on seasonal snow cover in Japan is still lacking. These motivated us to develop a coupled system that consists of the Japan Meteorological Agency (JMA)’s operational convection-permitting regional atmospheric model Local Forecast Model (LFM), Radar/Raingauge-Analyzed Precipitation (R/A) data, as well as the snow physics model Snow Metamorphism and Albedo Process (SMAP). The horizontal resolution of the current system is 1 km. We have evaluated the system in terms of SWE and confirmed that the obtained normalized root mean square error and normalized bias fall within the range of the snow model performances previously reported by the ESM-SnowMIP project. Numerical model simulations with the system during the 2017–2022 winters indicate that the seasonal peak area-integrated SWE in Japan reaches 42.2 Gt on average. It is unveiled that the 2017–2022 five-year-averaged March snow-covered-area-average SWE is 228 mm, which is 2.3 times higher than the 1980–2018 snow-covered-area-average SWE for the Northern Hemisphere above 40° N. We also highlight that the system has been used in JMA operationally since the 2022–2023 winter, where Snow Depth Analysis and Snowfall Amount Analysis, and Very Short-range Forecasts of Snow with a spatial resolution of 5km are issued hourly (https://www.jma.go.jp/bosai/en_snow/).

Beschreibung: Japan has a wide variation in the snowy environments and it is anticipated that climate change will alter the snow-cover conditions. Although a lot of meteorological observation sites managed by the Japan Meteorological Agency are located in the low altitude areas, few observation sites are located in the high altitude areas. Therefore, quantitative variations in snow conditions in Japan's mountainous regions are not yet well understood due to the lack of long-term observational data. The Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Resilience has managed a Snow and Weather Observation Network, operating for over 25 years, covering the northern part to the western part of Japanese mountains, which monitors fluctuations in meteorological and snow cover conditions in high altitude areas. These data are used not only to investigate the influence of climate change on snowy environments in Japan but also to mitigate snow disasters which have changed drastically in frequency and intensity owing to the changes in climatic conditions. Our long-term observations revealed that the trends of variation of maximum snow depth and maximum snow water equivalent are almost the same, but the range of variation of maximum snow water equivalent is larger than that of maximum snow depth. It was also found that the trend of variation of the maximum snow depth depends on elevation and that the variation may differ between mountainous and flat areas.