In order to analyse the relationship of air temperature to the growth of crops, the classificatory constitution of air temperature during the growth stages of crops should be clarified. But the assumption of such classification from the recording paper is troublesome and collection of recording papers from various places is difficult. From these reasons, the writer tried to obtain the classificatory constitution by calculation through the typification of diurnal variations of air temperature.
Assuming that θ
min shows minimum air temperature and that
R represents diurnal range of air temperature, θ
t showing air temperature at the time of
t becomes as follows:
θ
t=θ
min+a
tR (1)
where
at is the coefficient of diurnal range of air temperature. Through the same procedure, θ
0 showing mean daily air temperature follows as
θ
0=θ
min+a
DR (2)
where
aD shows the average of
at.
The average air temperature θ
m otained from the daily maximum and the minimum is as follows:
θ
m=θ
min+0.50R (3)
From formulas (2) and (3)
aD is obtained:
a
D=0.50-Δθ/R (4)
where Δθ=θ
m-θ
0.
The monthly average values of
aD calculated from (4) by use of the data from the main stations in Japan are shown in Fig. 1.
The distribution of annual variation of
aD classified as A
1, A
2, B and C types is shown in Fig. 3. The average
aD ranging from May to August becomes 0.45 in Japan (Fig. 3). By drawing both diurnal variation curves of air temperatures having various
aD values (Fig. 4) and the curve (
C-curve) put the case that the emergence times of the maximum and the minimum points on a sine-curve are distorted as 5a.m. and 2p.m., Δ
t showing the difference of emergible time more than constant
at obtaind from both diurnal variation curve of air temperature having certain
aD value and
C-curve was obtained (Fig. 5). Δ
t was ascertained to be -1.3 hours in the case of
aD=0.45 and
at=0.1-0.9. As the emergible time of
C-curve at the case of more thanconstant
at value is equal to the case of sine-curve, it is probable to obtain the emergible time by the calculation and the curve for
aD=0.45 can be obtained by adjusting Δ
t, -1.3 hours (Fig. 7,
S-curve). An example for the diurnal variation
S-curve of air temperature was shown in Fig. 4 (full line). Such
S-curve will be taken as a typical diurnal variation curve of air temperature during summer season in Japan. By using
S-curve, the emergible times of classificatory air temperatures will be easily obtained from Fig. 6, when the air temperature is substituted by
at in a formula (1).
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