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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2018-195
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Technical note
16 Apr 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).
Technical note: rectifying systematic underestimation of the specific energy required to evaporate water into the atmosphere
Andrew S. Kowalski 1Departmento de Física Aplicada, Universidad de Granada, Granada, 18071, Spain
2Instituto Interuniversitario de Investigación del Sistema Tierra en Andalucía, Centro Andaluz de Medio Ambiente (IISTA-CEAMA), Granada, 18071, Spain
Abstract. Not all of the specific energy consumed when evaporating water into the atmosphere (λ) is due to the latent heat of vaporization (L). What L represents is the specific energy necessary to overcome affinities among liquid water molecules, neglecting the specific work done against atmospheric pressure (p) when water expands in volume (V) from liquid to gas (pV work). Here, in the one-dimensional context typifying micrometeorology, the pV work done in such an expansion is derived based on the Stefan flow velocity at the surface boundary, yielding a simple function of the virtual temperature; additionally, an empirical formula is provided that approximates λ quite accurately over a useful range of environmental conditions. Neglect of this pV work term has caused a systematic 3–4 % underestimation of λ, and to some extent inhibited closure of the surface energy balance.
Citation: Kowalski, A. S.: Technical note: rectifying systematic underestimation of the specific energy required to evaporate water into the atmosphere, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2018-195, in review, 2018.
Andrew S. Kowalski
Andrew S. Kowalski
Andrew S. Kowalski

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Short summary
This technical note derives the additional specific energy of evaporation, beyond the latent heat of vaporization, as the work done against ambient pressure when water expands from the liquid to the gas phase. The derivation yields a simple function of the virtual temperature, and corrects for a systematic 3–4 % underestimation of the energy required to evaporate water into the Earth's atmosphere.
This technical note derives the additional specific energy of evaporation, beyond the latent...
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