An observation of various temperatures influenced by windbreak net was carried out at the paddy rice fields in Naganuma, Hokkaido from June 22 to July 1, 1978. As the decreasing effect of windspeed has been considerably recognized by many other references until now, an investigation was done only on a subject of various temperatures,
i.e., leaf, air, water and ground temperatures.
The following results were obtained.
Under the condition of overcast weather and “cutoff” flood irrigation system on June 22, the increasing rates of temperatures are 0.3 to 1.0°C for
tl (surface leaf-stem temperature) and 0.8 to 1.6°C for
tw (surface water temperature) measured by precision radiation thermometer at the point from -2H (distance represented windbreak height) (minus sign denotes windward side) to 10H. The reference temperature denotes the value at the point of -20H.
In the case of clear weather and “cutoff” flood irrigation system on June 23 to 24, the increasing rates of temperatures are 0.2 to 1.4°C for
tl, 0.9 to 2.3°C for
tw, 0.3 to 1.0°C for
Tl (leaf temperature), 0.2 to 0.9°C for
Ta (air ternperature), 0.9 to 2.2°C for
Tw (water temperature) and 0.9 to 2.0°C for
Tg (ground temperature) measured by thermo-junction thermometer. Maxima of temperature differences between 2H and 30H were 2.7°C for
tl at 1700 June 23, 3.8°C for
tw at 1515 June 23, 2.0°C for
Tl at 1220 June 24, 2.8°C for
Tw at 1220, 3.5°C for
Ta at 1300 June 23 and 3.8°C for
Tg at 1300.
Under the circumstance of overcast weather and “continuous” flood irrigation system on June 30 and July 1, the increasing rates of temperatures are 0.2 to 0.6°C for
tl, 0.5 to 1.0°C for
tw, 0.4 to 1.1°C for
Tl, 0.3 to 1.0°C for
Ta, 0.8 to 1.1°C for
Tw and 0.8 to 1.1°C for
Tg.
An interesting result was come up that the increasing temperatures at the distance of 1H just behind the windbreak were lower than those at the distances of -2H and 2H,
i, e., the values from 0800 to 1230 for
tl, from 1200 to 1515 for
tw, from 1300 to 1720 for
Tl and from 2230 to 0630 for
Tw, and the greater parts of values from 0920 to 1720 for
Ta and from 1220 to 0330 for
Tg. This seems to be mainly based on the reason that the adiabatic cooling wind of pretty high speed blows through the open space of 25cm between the net and the ground, and the increments of latent and sensible heat fluxes by increasing windspeed.
The temperature difference for
twl on June 22 is 1.7 to 2.7°C and ones for
twl and
Twl are 3.1 to 4.1°C and 3.7 to 5.1°C, respectively,
Tla is -0.0 to 0.4°C at the points from 1H to 20H and
Tgw at the points from 5H to 7.5H is 0.1 to 0.2°C and-0.1 to-0.5°C at other points, particularly -0.9°C at 1H on June 23 to 24. The value of
twl,
Twl,
Tla and
Tgw are 2.2 to 2.6°C, 2.3 to 2.5°C, 0.1 to 0.3°C and 0.1 to 0.5°C on June 30 and July 1, respectively.
According to the observation results mentioned above, it is considered that the region considerably effected by windbreak is from 5H in the windward side to 20H in the leeward side.
The appearances of maximum and minimum of
tl,
Tl and
Ta are generally earlier than thoseof
tw
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