A model for the water regime of a deciduous forest

The relationships between actual evapotranspiration, atmospheric conditions and soil water content in the root zone are described in a simple functional model. Some constants which are used in these relationships, but unknown for forest areas, have been estimated for a deciduous forest near Zürich in Switzerland (Brülhart, 1969). On sufficiently humid soil the evapotranspiration of this forest was more than twice as high as for agricultural crops. On the other hand in the forest the evapotranspiration reacted much more sensitively on drying of the soil. On warm summer days (evaporation of free water about 0.4–0.6 cm per day) the trees considerably reduced their water delivery to the atmosphere at soil water suctions of slightly more then 0.05 bars (Fig. 7).     

Measurements of solar occulation: the error in a naive retrieval if the constituent's concentration changes

The stratospheric concentrations of many minor constituents change rapidly at sunrise or sunset. If this happens, there is an inherent error when retrieving the vertical profiles of the constituents from measurements of their absorption of sunlight. For retrievals of NO at sunset the error can be estimated from in-situ measurements alone, without appeal to a model of stratospheric photochemistry. Below 20 km this error can approach 100% so that the retrieved NO is zero. But at 40 km, and at 25 km when the absorption is strong and Lorentzian, it can be less than 20%. Precise calculations of the error, even if small, require model calculations of the sunset and sunrise changes. With a model, we have calculated the error for NO, NO₂, OH and ClO.     

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