Abstract
Principal time and space variations of snowfall (precipitation) over the Japan Sea coastal region are described in terms of empirical orthogonal function (EOF). Daily precipitation data at -40 stations in 15 winters (30 months) are used.
The first two functions account for -65% of the total variance of precipitation. The spatical functions (B1 and B2) are related to the topography of the analyzed area. Basing on the magnitude of time variation functions (A1 and A2), we classify precipitation pattern of each day into three types; "mountain-", "normal-" and "plain-snowfall type". Inspecting time series of time variation functions for 30 months, we find that a certain snowfall type appears frequently in a particular winter. Especially P-type is dominant in the extraordinarily heavy snowfall winter.
In the latter part of this paper, we focus our attention on the heavy snowfall days (areaaveraged precipitation_??_20mm/day). The heavy snowfalls continue generally for a few days as a "heavy snowfall period", and a certain snowfall type tends to continue through a heavy snowfall period. It is inferred that the heavy snowfalls of a certain type occur under a certain large-scale situation. This will be studied in Part II of this paper.
