On the Distribution of Cyclonic Precipitation in Japan. 5 



position of the ''effective" centre, M'ithout making more or less 

 uncertain assumptions. Since it Avas our immediate purpose to 

 investigate the distribution for an isolated simple depression and 

 discuss the results from the theoretical standpoint, all these ambi- 

 guous cases were excluded, confining our attention only to the 

 simplest cases where only one conspicuous depression is shown in 

 the chart. ^ It must be admitted that in adopting this selection, 

 we are taking only those precipitations in consideration which 

 correspond to a quite limited weather type, and hence that the 

 whole subsequent discussion has no reference to the cases of preci- 

 pitations of noncyclonic type. Again, since each district includes 

 a numljer of stations, it occurs as a rule that for each position of the 

 centre, many districts have only partial rain or snow. Those cases 

 with precipitation in only one station, Ijut with none in the others, 

 were counted as " no precipitation,"' otherwise as " precipitation " 

 for that district. It must be remarked that the hours to which the 

 weather charts refer are limited to 6a, :2p, lOp, while the distribu- 

 tion of precipitation in other hours may often A'ary widel}^ lUit 

 f()r the present investigation, the three observations in a day seem 

 to be more than sufficient. Finally it must be i-emarked that the 

 cases in which there exists a centre of depression in the chart. l)Ut 

 with no precipitation in either station, were excluded. Such a c;ise, 

 wliich is only met with when the centre is near the margin of the 

 chart, is rather rare and the corresponding position of the centre 

 more or less doubtful. At any rate, the weight of these extreme 

 positions for the result is small and ]nust be taken into considera- 

 tion, if at all, with precaution. 



The statistical part of the investigations was chiefly carried 

 out by Yokota and Otuki. The number of times n in which the 

 ''precipitation" occurred in a given district, say Pi, corresponding 

 to a given position of the depression, say A, divided 1)}' the num- 

 Ijer of times N in which the centre was found in the area A, ex- 

 pressed in percent, was called the " expectation " of precipitation 

 for tlie pair (Pi, A). Tlie result of the statistical part is shown in 

 Table I. The first column gives the positions of the centre of 



* In such cases, the ijosition of the centre could he determined with a fair degree of 

 certainty. 



