Interpretability of negative latent heat fluxes from eddy covariance measurements in dry conditions

Abstract λ E) flux measurements under dry conditions, but a systematic assessment of the use of negative λ E fluxes from EC flux stations to characterize adsorption is missing. We propose a classification method to characterize soil water vapor adsorption, excluding conditions of dew and fog when λ E derived from EC is not trustworthy due to stable atmospheric conditions. We compare downwardly directed λ E fluxes from EC with measurements from weighing lysimeters for 4 years in a Mediterranean savanna ecosystem and 3 years in a temperate agricultural site. Our aim is to assess if overnight water inputs from soil water vapor adsorption differ between ecosystems and how well they are detectable by EC. λ E fluxes of which 88.8 % were confirmed to be soil water vapor adsorption by at least one lysimeter. At the temperate site, downwardly directed λ E fluxes were only recorded during 15 % of the nights, with only 36.8 % of half hours matching simultaneous lysimeter measurement of soil water vapor adsorption. This relationship slightly improved to 61 % under bare-soil conditions and extreme droughts. This underlines that soil water vapor adsorption is likely a much more relevant process in arid ecosystems compared to temperate ones and that the EC method was able to capture this difference. The comparisons of the amounts of soil water vapor adsorption between the two methods revealed a substantial underestimation of the EC compared to the lysimeters. This underestimation was, however, comparable with the underestimation in evaporation by the eddy covariance and improved in conditions of higher turbulence. Based on a random-forest-based feature selection, we found the mismatch between the methods being dominantly related to the site's inherent variability in soil conditions, namely soil water status, and soil (surface) temperature. We further demonstrate that although the water flux is very small with mean values of 0.04 or 0.06 mm per night for EC or lysimeter, respectively, it can be a substantial fraction of the diel soil water balance under dry conditions. Although the two instruments substantially differ with regard to the measured ratio of adsorption to evaporation over 24 h with 64 % and 25 % for the lysimeter and EC methods, they are in either case substantial. Given the usefulness of EC for detecting soil water vapor adsorption as demonstrated here, there is potential for investigating adsorption in more climate regions thanks to the greater abundance of EC measurements compared to lysimeter observations.

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch

Verweise und Beziehungen

• Erschienen in: Interpretability of negative latent heat fluxes from eddy covariance measurements in dry conditions ; volume:21 ; number:8 ; year:2024 ; pages:2051-2085 ; extent:35 ; Biogeosciences ; 21, Heft 8 (2024), 2051-2085 (gesamt 35)

Beteiligte, Orts- und Zeitangaben

• Urheber: Paulus, Sinikka J. ; Orth, René ; Lee, Sung-Ching ; Kleidon-Hildebrandt, Anke ; Jung, Martin ; Nelson, Jacob A. ; El-Madany, Tarek S. ; Carrara, Arnaud ; Moreno, Gerardo ; Mauder, Matthias ; Groh, Jannis ; Graf, Alexander ; Reichstein, Markus ; Migliavacca, Mirco

Weitere Informationen

• DOI: 10.5194/bg-21-2051-2024
• URN: urn:nbn:de:101:1-2405020439013.876024665127
• Rechteinformation: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 14.08.2025, 10:47 MESZ