On the Processes of Transitions between Circulation Regimes during Winter over Eurasia

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  • 冬季のユーラシア大陸上における異なった天候レジーム間の遷移過程
  • トウキ ノ ユーラシア タイリクジョウ ニ オケル コトナッタ テンコウ レジ

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Abstract

An investigation is made into the characteristics of different circulation regimes during winter over Eurasia and the processes of transitions between these regimes.<br> On the basis of 5-day mean 500mb height data over Eurasia during the 1946-1985 winters, the teleconnection patterns for two principal components- (E1: positive over the high latitudes and negative over the middle latitudes in Eurasia, and E2: positive over Europe, negative over Siberia and positive over the area near Japan, what we call the EU pattern)-were obtained by means of a principal component analysis (Fig. 2). Taking into account component scores, circulation regimes of four types (E1+, E1- E2+ and E2-) were extracted.<br> Stationary wave behavior for the persistent circulation regimes of each type was investigated by computing the activity flux of stationary waves. It was found that the propagation of stationary wave activity is scarcely seen over Eurasia for E1+ and E1-, while the activity of stationary waves largely propagates from Europe to East Asia for E2+ and E2- (Fig. 5).<br> On the basis of 500 mb height data measured twice daily, the extended E-P flux was calculated for the persistent circulation regimes of each type. The result showed that transient waves have a tendency to maintain circulation regimes of any type (Fig. 6).<br> Transitions between different persistent circulation regimes were also investigated by use of a composite analysis. The appearance of the North Atlantic Oscillation (NAO) pattern, preceding the occurrences of E2+ and E2-, were found (Fig. 7 and Fig. 8). However, a lag linkage from the NAO pattern to the appearance of E2+ or E2-do not always occur. Whether this lag linkage occurs or not is highly dependent on the circulation regime type in the pentads when the NAO pattern appears (Tables 2 and 3). Furthermore, the NAO pattern that has a sign opposite to that preceding the appearance of E2+ or E2- plays an important role also in the disappearance of E2+ or E2- (Figs. 13, 14, and 15).

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