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| Fig. 2.1.8. Energy transformation changes the meteorological parameters during the day and night in (A) a wheat field and (B) a coniferous forest. Rn Radiation balance; u wind speed; Tair temperature; e vapour pressure; c C02 concentration. During the day, absorbed radiation leads to a rise in temperature and an increase in vapour pressure. The C02 concentration is minimal at the height of the assimilating layer of leaves. The wind speed is reduced. During the night, there is a net loss of energy. This leads to the minimum temperature at leaf height. The C02 concentration is maximal at the soil surface. Due to the lower surface roughness, the gradient in wheat fields is more marked than in a forest. From the rise in the profile, the energy and mass balance can be calculated (wheat: after Monteith 1973; spruce: compiled by C. Rebmann)

T e hPa 10vpm c

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