Journal of the Japanese Society of Snow and Ice

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Marked concave-type depressions were observed in the intra-seasonal variability of the snow depth records in Sugadaira highlands, central Japan. The unique snow depth changes were associated with passing extra-tropical cyclones and occurred during the core-winter season. According to a simple heat-budget analysis with pit works, the sensible heat, which was dominant during the warm advections due to a cyclone, melted the snow surface, and during a non-precipitation period, the following re-freezing processes at the upper layers period maintained a flat snow level for several days. Snow depth records since 1967 showed the beginning of the concave-type depression after the winter of 1987/88; this period corresponded to the time when heavy snow winters ceased to exit in the coastal areas of Japan Sea. Two atmospheric teleconnection patterns, such as Pacific-North American (PNA) and Western Pacific (WP) patterns, also modulated their appearance after 1990, indicating the changes in the strike direction of the cyclone track toward the north. A significant increase in the winter precipitation amount with a decrease in the averaged center pressure of the cyclones passing over the Japan Sea was found. However, the statistical relationship between the cyclone activity and the occurrence of the abrupt snow depth variability was not identified. A long-term observation of the changes in the cryosphere at the high-elevations of central Japan is planned.

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A simple modeling method for estimating the outflow from the bottom of a snowpack during the spring melt season is proposed; this model can be used in distributed applications for preventing snowmelt-induced landslide hazards in mountainous regions. A temperature-radiation index melt model (Konya et al.,2004) is applied to the results of heat balance observations carried out at Oshirakwa in Niigata Prefecture in the winter of 2007/08 in order to calibrate the coefficients of the model. Estimated global radiation using a locally calibrated Angstrom model (Yang and Koike,2005) with duration of sunshine at the nearest AMeDAS station can be used as an input to the melt model. The percolation of water through a snowpack is modeled using a linear reservoir with a discharge coefficient that varies with a change in the snow depth (Nakatsugawa et al.,2004). Moreover, a new parameterization of the discharge coefficient with positive degree-day is applied for this percolation model. It is found that this combination of a melt model and a percolation model yields good estimates of outflow from the bottom of a snowpack at 1-hour intervals in the latter stage of the melt season when the following three input data are available : air temperature, global radiation (or duration of sunshine), and rainfall intensity.

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