This study focuses on the application of a modified digital elevation model (DEM) method that not only considers geometrical power losses but also addresses effects such as power losses caused by ground-clutter filtering and the radar system’s calibration errors. X-band dual-polarization radars operated by the Ministry of Land, Infrastructure, Transport and Tourism of Japan are located near mountainous terrain in the southern part of the Kanto region in Japan, at Fujinomiya and Shizukita. Both radars suffer from problems caused by partial beam shielding at various low-elevation angles, which lead to underestimation of the amount of rainfall. After correcting for reflectivity attenuation, a modified DEM method was applied to correct for bias reflectivity in the presence of beam-shielding problems. Validation of the corrected reflectivity based on comparison tests shows that the modified DEM method significantly improved the bias reflectivity caused by partial beam blocking.
A thick snow band often forms along the Okhotsk Sea coast of Hokkaido Island, northern part of Japan. Numerical simulations were made to investigate the formation and maintenance mechanisms of a long-lasted snow band appeared on 26th of December 2008 using Weather Research and Forecasting Model (WRF). The snow band was simulated along the coast of Hokkaido Island, moved offshore toward the Sea of Okhotsk, where it intensified, and was sustained for one and a half days. The results show that Sakhalin Island plays an important role in the maintenance of a convergence line and thus the snow band. Cold air advection from Sakhalin Island produces a strip of warm air between the advected cold air and Hokkaido Island and thus controls the location of the snow band, while topographic blocking by Sakhalin creates the lower level convergence at the Soya Strait and hence enhances the snow band. Temperature and surface-roughness contrast between Hokkaido Island and the Sea of Okhotsk appear to be also important for the initial formation of the snow band.
This study investigates the potential impacts of regional climate change on hydrological cycles using eight years of observations on snowmelt runoff from a small forested watershed (Kurahone watershed) in Nagano Prefecture, Japan. We compared discharge in winter and spring (January–May) in 1991, 1997, 1998, 2003, 2004, 2006, 2012 and 2013. Early years (1991, 1997, 1998 and 2003) were characterized by concentrated-type hydrographs, with concentrated discharge in the beginning of April due to overlaps in snowmelt and rainfall. Later years (2004, 2006, 2012 and 2013) were characterized by sporadic-type hydrographs, with several discharge peaks in midwinter due to rainfall and relatively low ratios of discharge in April to discharge during January to May. Tank-model calculations of discharge rate and snow water equivalent (SWE) over the last 21 years suggest that sporadic-type hydrographs have occurred more frequently in recent years, whereas average air temperature, precipitation amounts and SWE have no increasing or decreasing trends. Discharge in April increased with high maximum SWE and heavy rainfall in April, but decreased with increase of ratios of rainfall to total precipitation in winter. Regional climate change may drive increased midwinter rainfall and the absence of overlaps in snowmelt and rainfall in recent years.