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| Titel |
Deuterium excess as a proxy for continental moisture recycling and plant transpiration |
| VerfasserIn |
F. Aemisegger, S. Pfahl, H. Sodemann, I. Lehner, S. I. Seneviratne, H. Wernli |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 8 ; Nr. 14, no. 8 (2014-04-23), S.4029-4054 |
| Datensatznummer |
250118632
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| Publikation (Nr.) |
 copernicus.org/acp-14-4029-2014.pdf |
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| Zusammenfassung |
| Studying the evaporation process and its link to the atmospheric circulation
is central for a better understanding of the feedbacks between the surface
water components and the atmosphere. In this study, we use 5 months of
deuterium excess (d) measurements at the hourly to daily timescale from
a cavity ring-down laser spectrometer to characterise the evaporation source
of low-level continental water vapour at the long-term hydrometeorological
monitoring site Rietholzbach in northeastern Switzerland. To reconstruct the
phase change history of the air masses in which we measure the d signature
and to diagnose its area of surface evaporation we apply a Lagrangian
moisture source diagnostic. With the help of a correlation analysis we
investigate the strength of the relation between d measurements and the
moisture source conditions. Temporal episodes with a duration of a few days
of strong anticorrelation between d and relative humidity as well as
temperature are identified. The role of plant transpiration, the large-scale
advection of remotely evaporated moisture, the local boundary layer dynamics
at the measurement site and recent precipitation at the site of evaporation
are discussed as reasons for the existence of these modes of strong
anticorrelation between d and moisture source conditions. We show that the
importance of continental moisture recycling and the contribution of plant
transpiration to the continental evaporation flux may be deduced from the
d–relative humidity relation at the seasonal timescale as well as for
individual events. The methodology and uncertainties associated with these
estimates of the transpiration fraction of evapotranspiration are presented
and the proposed novel framework is applied to individual events from our
data set. Over the whole analysis period (August to December 2011)
a transpiration fraction of the evapotranspiration flux over the continental
part of the moisture source region of 62% is found albeit with a large
event-to-event variability (0% to 89%) for continental Europe.
During days of strong local moisture recycling a higher overall transpiration
fraction of 76% (varying between 65% and 86%) is found. These
estimates are affected by uncertainties in the assumptions involved in our
method as well as by parameter uncertainties. An average uncertainty of 11%
results from the strong dependency of the transpiration estimates on the
choice of the non-equilibrium fractionation factor. Other uncertainty sources
like the influence of boundary layer dynamics are probably large but more
difficult to quantify. Nevertheless, such Lagrangian estimates of the
transpiration part of continental evaporation could potentially be useful for
the verification of model estimates of this important land–atmosphere
coupling parameter. |
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