The monthly amount of summer Precipitations in Japan can be possibly forecasted by the 200mb height circulation trends in the preceeding month. The differences of monthly mean 200mb gpm, for instance, [Shionomisaki (33°27'N, 135°46'
E
)- Wajima (37°23'N, 136°54'
E
)] in June, show surprising correlations with the amount of precipitations in July at many places and various districts in Japan, and the correlation coefficients with July precipitations, for example, of the western part of Japan and Hokkaido, are as follows.
(a) The total amount of July precipt. at 5 places in western Japan ;
Fukuoka (33°35'N, 130°23'
E
), Oita (33°14'N, 131°37'
E
), Shimonoseki (33°57'N, 130°56'
E
), Hagi (34°25'N, 131°24'
E
), and Hofu (34°03'N, 131°32'
E
).
R=+0.
93
for the years of period (1950-1459, n=10)
(b) The total amount of July precipt, at 5 places in Hokkaido ;
Suttsu (42°47'N, 140°14'
E
), Sapporo (43°03'N, 141°20'
E
), Asahikawa (43°46'N, 142°
22
'
E
), Haboro (44°
22
'N, 141°42'
E
), and Wakkanai (45°25'N, 141°41'
E
).
R=-0.
83
for the years of period (1950-1959, n=10)
As shown in Fig. 4 (A), above normal strength of mean jet streams in southern part of Japan is related contemporarily to the rainfall distribution, above normal in southwestern part of Japan and below normal in Hokkaido, and vice versa. Because of persistence of the tendency to maintain itself in a given state of circulation in upper air, the zonal index at 200mb height adequately adopted for the stations in southern part of Japan, may be presumed to be closely related to the precipitations in the following month.
As a test of stability of the forecasting relationships, which were obtained from the data in the recent only 10 years or so, since the establishment of systematic upper air observations in Japan, it is investigated that below normal air temperatures in early summer from April to June at mountain observatories in western Japan, which suggest the upper air flow patterns with deep trough over the Japan Sea and above normal strength of mean jet over the southwestern part of Japan, tend to be favorable to above normal July precipitations in the western Japan and vice versa. The correlation coefficient of the mean air temperatures of April, May and June at Hieizan (35°03'N, 135°50'
E
, 832m) with the amount of July precipitations in the district along the Inland Sea [totals for 5 places, Shimonoseki, Matsuyama (33°50'N, 132°47'
E
), Hiroshima (34°
22
'N, 132°26'
E
), Okayama (34°41'N, 133°55'
E
), and Tadotsu (34°16'N, 133°45'
E
)] is R=-0.51 (for the years of period 1929-1947, n=19), while the coefficient of June air temperature at Asosan (32°53'N, 131°05'
E
, 1143m) with the July precipitations in the western part of Kyushu [totals for 4 places, Izuhara (34°12'N, 129°18'
E
), Tomie (32°37'N, 128°46'
E
), Nagasaki (32°44'N, 129°53'
E
), and Unzendake (32°44'N, 130°15'
E
)] being R=-0.49 (for the period 1923-1952, n=20).The results of applications of the relationships to the forecasting of monthly amountof rainfalls in May, June and July in this year are very satisfactory, as seen inFig.9 (A), (B), (C).
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