Abstract
Yearmto-year variations of winter air temperatures over the Far East are not uniform throughout the region. The objectives of this study are to determine the regional differences in winter temperature variations over the Far East and the relationship between these regional differences and hemispheric temperature variations.
1. The factor analysis method was applied to mean January temperature data for the period 1901 1975. Two main factors were extracted to explain more than 60% of the cumulative variance in winter temperatures over the Far East (Table 1). The distribution of factor loadings (Fig. 2) suggests that the first factor is associated with anomalies of opposite signs over southwestern Japan and the Sea of Okhotsk, whilst the second factor is associated with an anomaly located in a region stretching from Lake Bikal to Hokkaido.
2. Correlation coefficients were calculated between factor scores and 500 mb heights over the Northern Hemisphere (Fig. 3), zonal wind components at the 500 mb level (Fig. 4), and surface pressure gradients (Table 2), and the relationships between factor scores and the distribution of surface fronts were examined (Fig. 6). It was found that the first factor is associated with variations in the circulation pattern of the westerlies between a zonal pattern and a meridional one, and that the second factor is associated with variations in the strength of the westerlies around Lat. 40°N.
Winter temperature anomaly patterns over the Far East were classified into four types on the basis of factor scores, and it was found that each type is associated with a particular circulation pattern. There four circulation patterns are shown schematically in Fig. 7.
Of these four types, I and 1 represent two typical patterns which bring cold winter to Japan. The former brings cold spells lasting a week or more to southwestern Japan, whilst the latter brings cold spells lasting less than a week to northern Japan (Fig. 8).
3. Long term changes in temperatures were identified by factor analysis of data for six periods (1901_??_30, 1911_??_40, 1921_??_50, 1931_??_60, 1941_??_70, 1946_??_75) (Table 3). It was found that the anomalies identified by the first and second factors moved northward over a period of time, reaching their most northerly locations during the third period (1921_??_50), when temperatures in the high latitude regions of the Northern Hemisphere also reached a maximum, and that they then gradually move southwards, a movement that has continued up to the present (Fig. 9). This indicates that the structure of winter temperature variation over the Far East has shifted north and south in accordance with the rise and fall of air temperature in the high latitude region of the Northern Hemisphere.
4. The first factor shows a 20_??_25 year periodicity, and the second factor shows a 7_??_8 year periodicity. The latter periodicity is similar to that found in the August temperatures in Japan.
The author come to the conclusion that year-to-year variations of winter air temperatures over the Far East result from these two rythms as well as from latitudinal shifts in the structure of winter temperature variations.
