Basic data are arranged to explain the author's newly proposed practical rules for predicting some chief characteristics of Bai-u in West Japan by the aerological data at MarcusIsland one month before.
The rules are as follows :
(i) Setting in of Bai-u for any year occurs 31 days after the appearance of phase " I ", i.e. the day from which onward the upper wind at 18km height over Marcus changes from westerly to easterly, and ending of Bai-u also occurs 31 days after the appearance of phase " S ", i.e. the day from which the easterly wind velocity at 18km height over Marcus becomes to exceed 10m sec-1 for at least 5 days. Accordingly, the days between phase "I" and "S" give the period of Bai-u for any year.
(ii) The 31st day after the appearance of the peak (maximum) in T curve, i. e. a curve showing the day to day change of tropopause height at Marcus during phase I-S, corresponds to the principal rainy day of West Japan. Here the principal rainy day (PRD) is defined as follows : when the rainfall terminates in a day, its day is PRD, while, when the rainfall continues over two days, a day of the largest daily amount is PRD.
(iii) If the easterly wind blows continuously during phase I-S, the rainy season of land rain and low temperature can be expected, and the dry rainy eason may correspond to a few occurrence of the easterly wind. And the other case corresponds to the rainy season of shower and high temperature.
(iv) The larger range among mean wind velocity less than 10m sec-1 at 12Z of each day and that more than 10m sec-1 of the easterly wind during phase I-S, gives the largest amount of rainfall during Bai-u period.
(v) The daily amount of heavy rainfall during the Bai-u period can be expected 31 days after the appearance of HR type i. e. the peak of T curves at Marcus Island corresponding to the trough at 100mb and 200mb levels.
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