title: Latent heat exchange in the boreal and arctic biomes.
abstract: In this study latent heat flux (λE) measurements made at 65 boreal and arctic eddy-covariance (EC) sites were analyses by using the Penman-Monteith equation. Sites were stratified into nine different ecosystem types: harvested and burnt forest areas, pine forests, spruce or fir forests, Douglas-fir forests, broadleaf deciduous forests, larch forests, wetlands, tundra and natural grasslands. The Penman-Monteith equation was calibrated with variable surface resistances against half-hourly eddy-covariance data and clear differences between ecosystem types were observed. Based on the modeled behavior of surface and aerodynamic resistances, surface resistance tightly control λE in most mature forests, while it had less importance in ecosystems having shorter vegetation like young or recently harvested forests, grasslands, wetlands and tundra. The parameters of the Penman-Monteith equation were clearly different for winter and summer conditions, indicating that phenological effects on surface resistance are important. We also compared the simulated λE of different ecosystem types under meteorological conditions at one site. Values of λE varied between 15% and 38% of the net radiation in the simulations with mean ecosystem parameters. In general, the simulations suggest that λE is higher from forested ecosystems than from grasslands, wetlands or tundra-type ecosystems. Forests showed usually a tighter stomatal control of λE as indicated by a pronounced sensitivity of surface resistance to atmospheric vapor pressure deficit. Nevertheless, the surface resistance of forests was lower than for open vegetation types including wetlands. Tundra and wetlands had higher surface resistances, which were less sensitive to vapor pressure deficits. The results indicate that the variation in surface resistance within and between different vegetation types might play a significant role in energy exchange between terrestrial ecosystems and atmosphere. These results suggest the need to take into account vegetation type and phenology in energy exchange modeling.
authors.affiliation: Department of Forest Sciences, University of Helsinki, POBox 27, Helsinki, 00014, Finland; Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Ville
authors.initials: V
authors.lastname: Kasurinen
authors.forename: Knut
authors.initials: K
authors.lastname: Alfredsen
authors.forename: Pasi
authors.initials: P
authors.lastname: Kolari
authors.forename: Ivan
authors.initials: I
authors.lastname: Mammarella
authors.forename: Pavel
authors.initials: P
authors.lastname: Alekseychik
authors.forename: Janne
authors.initials: J
authors.lastname: Rinne
authors.forename: Timo
authors.initials: T
authors.lastname: Vesala
authors.forename: Pierre
authors.initials: P
authors.lastname: Bernier
authors.forename: Julia
authors.initials: J
authors.lastname: Boike
authors.forename: Moritz
authors.initials: M
authors.lastname: Langer
authors.forename: Luca
authors.initials: L
authors.lastname: Belelli Marchesini
authors.forename: Ko
authors.initials: K
authors.lastname: van Huissteden
authors.forename: Han
authors.initials: H
authors.lastname: Dolman
authors.forename: Torsten
authors.initials: T
authors.lastname: Sachs
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ohta
authors.forename: Andrej
authors.initials: A
authors.lastname: Varlagin
authors.forename: Adrian
authors.initials: A
authors.lastname: Rocha
authors.forename: Altaf
authors.initials: A
authors.lastname: Arain
authors.forename: Walter
authors.initials: W
authors.lastname: Oechel
authors.forename: Magnus
authors.initials: M
authors.lastname: Lund
authors.forename: Achim
authors.initials: A
authors.lastname: Grelle
authors.forename: Anders
authors.initials: A
authors.lastname: Lindroth
authors.forename: Andy
authors.initials: A
authors.lastname: Black
authors.forename: Mika
authors.initials: M
authors.lastname: Aurela
authors.forename: Tuomas
authors.initials: T
authors.lastname: Laurila
authors.forename: Annalea
authors.initials: A
authors.lastname: Lohila
authors.forename: Frank
authors.initials: F
authors.lastname: Berninger
mesh_terms: D001110:Arctic Regions; D001208:Asia; D017753:Ecosystem; D005060:Europe; D065928:Forests; D065948:Grassland; D006358:Hot Temperature; D008962:Models, Theoretical; D009656:North America; D065929:Tundra; D053833:Wetlands
keywords: eddy-covariance; evapotranspiration; latent heat; phenology; stomatal resistance