We examined interannual variation in snow-accumulation events in Tokyo and the relationship of this variation to large-scale atmospheric patterns. Years when snow-accumulation events occurred tended to coincide with a west-to-east wavetrain pattern in the middle and upper troposphere over Eurasia. The pattern, which includes cyclonic anomalies over Europe and East Asia and anticyclonic anomalies over Siberia, is identical to the negative phase of the Eurasian (EU) pattern, which is the leading mode of an empirical orthogonal function (EOF) analysis applied for the Eastern Hemisphere in the 500-hPa height field. Anomalous cold air associated with the negative EU pattern widely covers East Asia and Japan in the lower troposphere. No significant relation to storm-track activities around Japan was found except for extremely deep snowfall years. The cold atmospheric anomaly associated with the negative EU pattern possibly lowers the surface air temperature over Tokyo, creating an environment favorable to snowfall and snow accumulation. In the extremely deep snow years, the signature of the EU pattern was weak, and storm tracks over the ocean to the south of Japan were significantly active. No clear long-term trend in snow-accumulation events was found, although a downward trend due to anthropogenic effects was expected.
2007 by the Meteorological Society of Japan