Type of Diurnal Variations of Air Temperature during Summer Season in Japan

Studies on the Agro-climate No. 6

Abstract

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 a_t is the coefficient of diurnal range of air temperature. Through the same procedure, θ₀ showing mean daily air temperature follows as
θ₀=θ_min+a_DR (2)
where a_D shows the average of a_t.
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) a_D is obtained:
a_D=0.50-Δθ/R (4)
where Δθ=θ_m-θ₀.
The monthly average values of a_D 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 a_D classified as A₁, A₂, B and C types is shown in Fig. 3. The average a_D ranging from May to August becomes 0.45 in Japan (Fig. 3). By drawing both diurnal variation curves of air temperatures having various a_D 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., Δt showing the difference of emergible time more than constant a_t obtaind from both diurnal variation curve of air temperature having certain a_D value and C-curve was obtained (Fig. 5). Δt was ascertained to be -1.3 hours in the case of a_D=0.45 and a_t=0.1-0.9. As the emergible time of C-curve at the case of more thanconstant a_t value is equal to the case of sine-curve, it is probable to obtain the emergible time by the calculation and the curve for a_D=0.45 can be obtained by adjusting Δt, -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 a_t in a formula (1).