Dew formation in the rice canopy was directly observed to assess its actual nature and was simulated using a multilayer microclimate model to understand the relationship between the dew amount and atmospheric conditions. Observations were made on four nights during August and October in a paddy field in Kumamoto, Japan under warm temperate climate. The vertical profile of the dew amount in the canopy was measured every 2 h at 0.2 m intervals. The maximum dew amount was recorded in the early morning on all observation days. The total dew amount for the whole canopy at 6:00 on August 19, 21, and 24, and on October 1 was 0.10, 0.07, 0.15, and 0.23 mm, respectively. The dew amount determined from the simulation showed a good agreement with the actual observations. The dew amount per unit leaf area was larger in the upper layers than in the lower layers of the canopy on all days. This vertical difference in the dew amount was explained by the difference in effective radiation (net longwave radiation). The vertical gradient of the dew amount was steep on August 19 and October 1, whereas it was gentle on August 21 and 24. This difference in gradient was explained by the difference in paddy water temperature. When the water temperature was higher than the air temperature, the vertical gradient of the effective radiation and dew amount became steeper. The total amount and source of dew also varied with water temperature. The dominant source of dew was dewfall (water flux from the atmosphere) at lower water temperature, whereas it was distillation (water flux from the ground surface) at higher water temperature. From these results, we conclude that water temperature plays an important role in dew formation in the rice canopy.

中文翻译：

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水稻冠层露水形成观测及其多层微气候模型模拟

直接观察水稻冠层中的露水形成以评估其实际性质，并使用多层微气候模型进行模拟以了解露水量与大气条件之间的关系。8 月和 10 月期间，在日本熊本的暖温带气候条件下，在稻田中进行了四个晚上的观察。冠层露量的垂直剖面每 2 小时测量一次，间隔为 0.2 米。在所有观察日的清晨记录了最大露水量。8月19日、21日、24日6:00和10月1日全冠总露量分别为0.10、0.07、0.15和0.23毫米。由模拟确定的露水量与实际观察结果非常吻合。全天冠层单位叶面积露量上层大于下层。这种露量的垂直差异可以用有效辐射（净长波辐射）的差异来解释。8月19日和10月1日的露量垂直梯度较陡，8月21日和24日的露量垂直梯度较缓，这种梯度差异与稻田水温的差异有关。当水温高于气温时，有效辐射和露量的垂直梯度变陡。露水的总量和来源也随水温而变化。露水的主要来源是水温较低时的露水（来自大气的水通量），而水温较高时则是蒸馏（来自地表的水通量）。