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How representative are instantaneous evaporative fraction measurements for daytime fluxes ?

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons59571

Peng,  Jian
Terrestrial Remote Sensing / HOAPS, The Land in the Earth System, MPI for Meteorology, Max Planck Society;
IMPRS on Earth System Modelling, MPI for Meteorology, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons37109

Borsche,  Michael
Terrestrial Remote Sensing / HOAPS, The Land in the Earth System, MPI for Meteorology, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons37243

Loew,  Alexander
Terrestrial Remote Sensing / HOAPS, The Land in the Earth System, MPI for Meteorology, Max Planck Society;
CRG Terrestrial Remote Sensing, Research Area A: Climate Dynamics and Variability, The CliSAP Cluster of Excellence, External Organizations;

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Volltexte (frei zugänglich)

hess-17-3913-2013.pdf
(Verlagsversion), 714KB

Ergänzendes Material (frei zugänglich)

hess-17-3913-2013-supplement.pdf
(Ergänzendes Material), 2MB

Zitation

Peng, J., Borsche, M., Liu, Y., & Loew, A. (2013). How representative are instantaneous evaporative fraction measurements for daytime fluxes? Hydrology and Earth System Sciences, 17, 3913-3919. doi:10.5194/hess-17-3913-2013.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-0014-68F5-0
Zusammenfassung
Sun-synchronous optical and thermal remote sensing is a promising technique to provide instantaneous ET (evapotranspiration) estimates during satellite overpass. The common approach to extrapolate the instantaneous estimates to values for daily or longer periods relies on the assumption that the EF (evaporative fraction, defined as the ratio of latent heat flux to surface available energy) remains nearly constant during daytime. However, there is still no consensus on the validity of the self-preservation of the EF. We use FLUXNET (a global network of eddy covariance stations) measurements to examine this self-preservation, and the conditions under which it can hold. It is found that the instantaneous EF could represent daytime EF under clear sky conditions, especially between 11:00 and 14:00 LT (local time) for all stations. However, the results show that the EF is more variable during cloudy sky conditions, so that an increase in cloud cover results in an increase in the variability of the EF during daytime.