A Comparison of the Diel Cycle of Modeled and Measured Latent Heat Flux During the Warm Season in a Colorado Subalpine Forest
AuthorBurns, Sean P.
Swenson, Sean C.
Wieder, William R.
Lawrence, David M.
Bonan, Gordon B.
Knowles, John F.
Blanken, Peter D.
AffiliationUniv Arizona, Sch Geog & Dev, Coll Social & Behav Sci
MetadataShow full item record
PublisherAMER GEOPHYSICAL UNION
CitationBurns, S. P., Swenson, S. C., Wieder, W. R., Lawrence, D. M., Bonan, G. B., Knowles, J. F., & Blanken, P. D. (2018). A comparison of the diel cycle of modeled and measured latent heat ﬂux during the warm season in a Colorado subalpine forest. Journal of Advances in Modeling Earth Systems, 10, 617–651. https://doi. org/10.1002/2017MS001248
RightsCopyright © 2018. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
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AbstractPrecipitation changes the physiological characteristics of an ecosystem. Because land-surface models are often used to project changes in the hydrological cycle, modeling the effect of precipitation on the latent heat flux lambda E is an important aspect of land-surface models. Here we contrast conditionally sampled diel composites of the eddy-covariance fluxes from the Niwot Ridge Subalpine Forest AmeriFlux tower with the Community Land Model (CLM, version 4.5). With respect to measured lambda E during the warm season: for the day following above-average precipitation, lambda E was enhanced at midday by approximate to 40 W m(-2) (relative to dry conditions), and nocturnal lambda E increased from approximate to 10 W m(-2) in dry conditions to over 20 W m(-2) in wet conditions. With default settings, CLM4.5 did not successfully model these changes. By increasing the amount of time that rainwater was retained by the canopy/needles, CLM was able to match the observed midday increase in lambda E on a dry day following a wet day. Stable nighttime conditions were problematic for CLM4.5. Nocturnal CLM lambda E had only a small (approximate to 3 W m(-2)) increase during wet conditions, CLM nocturnal friction velocity u(*) was smaller than observed u(*), and CLM canopy air temperature was 2 degrees C less than those measured at the site. Using observed u(*) as input to CLM increased lambda E; however, this caused CLM lambda E to be increased during both wet and dry periods. We suggest that sloped topography and the ever-present drainage flow enhanced nocturnal u(*) and lambda E. Such phenomena would not be properly captured by topographically blind land-surface models, such as CLM.
NoteOpen access journal
VersionFinal published version
SponsorsU.S. DOE, Office of Science through the AmeriFlux Management Project (AMP) at Lawrence Berkeley National Laboratory ; NIFA/USDA grant [2015-67003-23485]; NCAR Mesoscale and Microscale Meteorology (MMM) Laboratory; NSF [DEB 1637686]; University of Colorado Boulder Libraries Open Access Fund; NSF