著者

斎藤 隆幸

出版者

日本農業気象学会

雑誌

農業気象 (ISSN:00218588)

巻号頁・発行日

vol.23, no.2, pp.65-74, 1967-09-30 (Released:2010-02-25)

参考文献数

9

被引用文献数

1 4

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In order to study the nocturnal cooling of plant communities, the fall of temperature of a wheat field during night was calculated for various values of net radiation and of wind speed above the surface of the wheat field, 60cm height and with 4.4 of L A I. The results of the calulation were compared with the fall of temperature of the bare soil surface during night.As it is observed that the thermal condition of the plant layer is approximately in equilibrium for the time just before sunrise, the vertical distribution of leaf temperatue, air temperature and water vapour density within the plant layer at the time of sunrise are calculated with various values of net radiation and of wind speed at the height 40cm above the surface of the wheat field on the assumption of equilibrium condition.The calculated profiles of leaf temperature and air temperature for 0.10cal·cm-2·min-1 of net radiation are shown in Fig. 4 for the values of 0.5m·sec-1 and 3.0m·sec-1 of wind speed. It is seen from Fig. 4 that difference between the temperatues of the upper part of plant layer and of soil surface under the plant layer is about 9.0°C for 0.5m·sec-1 of wind speed and about 0.5°C for 3.0m·sec-1.The fall of temperature during night was obtained from the difference between the calculated value of temperature and the temperature at the time of sunset. The temperature at the time of sunset was assumed to be equal to that at the top of the inversion layers. The fall of leaf temperature of the upper part of the wheat field, shown in Fig. 3, is in very close agreement with observational values. As seen in Fig. 3, the temperature fall increases rapidly with decreasing the wind speed below 1m/sec.The fall of temperature of the bare soil surface was also calculated for the radiation values and the wind speed at the height 50cm above the soil surface. The calculated results of the fall are in good agreement with those of BERLYAND (1956). The variation in the fall of temperature of the bare soil surface with wind speed is not so apparent as in the case of the wheat field.By use of both calculated results of the wheat field and of the bare soil surface, comparison was made of the fall of temperature of the upper part of the wheat field and of the bare soil surface under the same meteorological conditions. From the results it can be inferred that the night minimum temperature of the upper part of the wheat field is lower than that of the bare soil surface for the condition of calm wind, but that for windy condition the reverse is the case.