HR: 15:20h
AN: B23E-07    [Abstracts]
TI: What do the towers see at night? An exploration of nocturnal eddy covariance evapotranspiration fluxes from three adjacent ecosystems in the Southeastern U.S.
AU: * Novick, K A
EM: kan2@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AU: Stoy, P C
EM: paul.stoy@ed.ac.uk
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AU: Stoy, P C
EM: paul.stoy@ed.ac.uk
AF: Institute of Atmospheric and Environmental Sciences, School of GeoScienes, University of Edinburgh, 218 Crew Building, Kings Buildings University of Edinburgh, Edinburgh, EH9 3JN, United Kingdom
AU: Juang, J
EM: jj19@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AU: Siqueira, M B
EM: mbs4@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AU: Katul, G G
EM: gaby@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AB: While it is commonly assumed that stomatal closure prevents nocturnal transpiration in C3 plants, recent evidence from a number of studies suggests that significant transpiration occurs at night across a wide range of species. We explore the magnitude of nocturnal evaportranspiration (ET) fluxes measured by multiple years of eddy-covariance data from a successional gradient (grassland, planted pine forest, and hardwood forest) in the Southeastern U.S. all experiencing similar climatic and edaphic conditions. After removing unreliable data points collected during periods of low turbulence, nocturnal ET fluxes averaged 27.1, 19.1 and 5.5 percent of the magnitude of mean daytime ET fluxes in the grassland, pine forest, and hardwood forest, respectively. Because little attention has been paid to deriving appropriate methods to gapfill missing eddy covariance ET fluxes, we employed several gapfilling methodologies on these datasets, with a focus on assessing appropriate methods to gapfill nocturnal fluxes. These gapfilling procedues include multiple linear regression between nocturnal ET and meteorological variables (namely air temperature, vapor pressure deficit, and mean wind speed), relationships between nocturnal and daytime ET and conductance measurements, and a multiple imputation Monte Carlo technique. The utility of the gapfilling procedures is then assessed by comparing simulated fluxes to reliable measured fluxes using randomly generated gaps, and by assessing the difference between the annual sums of ET across these three sites as generated by the different gapfilling techniques. The seasonality of these nocturnal ET fluxes and their relationship to leaf area is also explored.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0466 Modeling
DE: 0495 Water/energy interactions (1878)
DE: 1818 Evapotranspiration
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting