A Study on the Unusual “Baiu” Season in 1954 by Means of Northern Hemisphere Upper Air Mean Charts

[摘要] In the early summer or “Baiu” season of 1954, Japan was dominated by abnormal coolness and persistent rain for nearly two months. In the present study, this abnormal weather condition is investigated based primarily on the 5-day mean and 30-day mean 500mb charts with a view to explain it in relation to the hemispherical pressure distribution.As a result, a world-wide stagnation of pressure pattern with a ridge over the Sea of Okhotsk is found to be responsible to the abnormality in the Far Eastern weather. Furthermore, it is shown that the “North High” situation which characterizes the weather in the Baiu season is closely related to the anticyclogenesis over certain climatologically defined localities and also to the position of the jet stream relative to the Himalayas.The findings for 1954 are then compared with the normal climatological statistics and their applicability to the Baiu season in general is proved. Finally, a hypothesis on the mechanism of the Baiu is proposed.

[学科分类] 大气科学