Interrelations of the Ice off Northern Japan and the Weather

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Abstract
An analysis of the historical series of ice appearance date at Abashiri in northern Hokkaido which on the average falls January 14, was made in terms of the mean monthly January pressure gradient over the northern Okhotsk Sea, and the preceding December pressure gradient upstream over northeastern Siberia, the results obtained showing a moderate relationship based on some 60 years of record and a somewhat closer relationship based on cases when the departure in the pressure gradient from the average equalled or exceeded ±0.8 the standard deviation, σ, suggesting a limited basis for predicting the ice appearance date in northern Hokkaido. Confirmatory evidence of the relationship of the January and preceding December pressure gradients to the north of Japan with the ice appearance date was obtained from an analysis of the frequency of lows crossing Hokkaido and its environs. A similar analysis of the ice disappearance date which on the average occurs April 22, shows a marked relationship with the contemporary April pressure gradient, but little, if any, relationship with the gradient to the north in March, presumably because of the discontinuous change in the general circulation during the spring in that general area. It is further shown that the date of ice appearance at Abashiri taken to reflect the circulation pattern over the general area, correlates moderately with the following mean monthly February air temperature over northeastern Hokkaido.