BORA AND OROSHI: THEIR SYNOPTIC CLIMATOLOGICAL SITUATION IN THE GLOBAL SCALE

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  • グローバルスケールでみたボラとおろし
  • グローバルスケール デ ミタ ボラ ト オロシ

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The occurrence frequencies in a half decade of the synoptic pattern suitable for developing bora on the Adriatic Coast of Jugoslavia during the ten-year-period of 1956-1965 (Fig. 1), reveals that the cyclonic bora, with which prolonged bora-days having a duration of 5 _??_ 7 days used to begin (Tab. 1), occurs mostly in winter half year. As one of the necessary conditions for bora, the cold polar air outbreak to East Europe, which is identified as a trough on the weather chart, plays an important role (Tab. 3, Fig. 2). Another cold polar air outbreak to East Asia causes oroshi in Japan, a local wind like bora (Fig. 3, Fig. 4).<br> The correlation coefficient between the monthly occurrences of bora and oroshi (Tab. 2, Tab. 4) is significant in winter months, especially in January.<br> The patterns of the topography at the 500 mb level in the northern hemisphere in January with infrequent bora and oroshi reveal in comparison with that of frequent bora and oroshi (Fig. 5) that for the former case a peculiar synoptic pattern can be distinguished (Fig. 6) as well as for the latter case.<br> The correlations between 5-day occurrences of bora and oroshi are, however, not significant in any case. This is thought because of the life time and scale of the upper troughs, through which both local winds can be connected with each other, is an order of 106-107 second or 10, 000 km. Therefore, it can be said, that as far as the monthly total number of bora-days and oroshi-days are concerned a close relation is found be-tween them, especially for January.

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