TY - JOUR
T1 - Reactive hydrocarbon flux footprints during canopy senescence
AU - Strong, C.
AU - Fuentes, J. D.
AU - Baldocchi, D.
N1 - Funding Information:
This material is based on work supported under a National Science Foundation (NSF) graduate research fellowship provided to C. Strong. J.D. Fuentes acknowledges NSF support through award OPP-0137420. Two anonymous reviewers provided excellent comments to improve the original manuscript. Prof. Timo Vesala, University of Helsinki, is acknowledged for inviting and providing partial funding for the authors’ participation in the Third INTAS Workshop on Flux and Concentration Footprints at the Hyytiälä Forestry Field Station, University of Helsinki, Finland.
PY - 2004/12/25
Y1 - 2004/12/25
N2 - A coupled Lagrangian random walk and atmospheric turbulence model was employed to investigate the magnitude of isoprene source distribution within a mixed deciduous forest canopy undergoing defoliation. Modeled source distributions were studied to understand how the flux footprint evolved as the total amount and vertical distribution of foliage changed during the leaf senescing and abscission period. The modeled ensemble air parcel residence times inside the forest canopy were also studied to quantify the fraction of isoprene destroyed inside forest canopies due to rapid chemical reactions. Defoliation in the canopy affected the footprint by vertically redistributing the flux sources, and by reducing the leaf drag area encountered by flows within the canopy. For air parcel releases in the upper canopy, the increased in-canopy turbulence associated with defoliation shifted the footprint peak probability closer to the measurement point. However, when integrated through the depth of the canopy, the net effect of defoliation was to increase the upwind source areas farther from the flux measurement point. Defoliation also impacted air parcel residence times within the canopy. Under fully foliated conditions, air parcels remained within the canopy for periods ranging from 2 to 50 min, depending on levels of atmospheric turbulence and air parcel release height. Under 25-75% defoliated conditions, air parcels remained in the forest canopy for periods lasting less than 10 min. The estimated air parcel residence times inside the fully leafed canopy resulted in significant isoprene chemical processing. Based on Lagrangian footprint simulations with active chemistry, the integrated rates of isoprene destruction from reactions with ozone, hydroxyl, and nitrate radicals ranged from 12% for air parcels released in the upper canopy to 40% for air parcels released from the lower canopy. We conclude that active scalar flux estimates, often based only on the footprint transfer function and source strength distribution, can be substantially improved by incorporating an active chemistry term.
AB - A coupled Lagrangian random walk and atmospheric turbulence model was employed to investigate the magnitude of isoprene source distribution within a mixed deciduous forest canopy undergoing defoliation. Modeled source distributions were studied to understand how the flux footprint evolved as the total amount and vertical distribution of foliage changed during the leaf senescing and abscission period. The modeled ensemble air parcel residence times inside the forest canopy were also studied to quantify the fraction of isoprene destroyed inside forest canopies due to rapid chemical reactions. Defoliation in the canopy affected the footprint by vertically redistributing the flux sources, and by reducing the leaf drag area encountered by flows within the canopy. For air parcel releases in the upper canopy, the increased in-canopy turbulence associated with defoliation shifted the footprint peak probability closer to the measurement point. However, when integrated through the depth of the canopy, the net effect of defoliation was to increase the upwind source areas farther from the flux measurement point. Defoliation also impacted air parcel residence times within the canopy. Under fully foliated conditions, air parcels remained within the canopy for periods ranging from 2 to 50 min, depending on levels of atmospheric turbulence and air parcel release height. Under 25-75% defoliated conditions, air parcels remained in the forest canopy for periods lasting less than 10 min. The estimated air parcel residence times inside the fully leafed canopy resulted in significant isoprene chemical processing. Based on Lagrangian footprint simulations with active chemistry, the integrated rates of isoprene destruction from reactions with ozone, hydroxyl, and nitrate radicals ranged from 12% for air parcels released in the upper canopy to 40% for air parcels released from the lower canopy. We conclude that active scalar flux estimates, often based only on the footprint transfer function and source strength distribution, can be substantially improved by incorporating an active chemistry term.
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U2 - 10.1016/j.agrformet.2004.07.011
DO - 10.1016/j.agrformet.2004.07.011
M3 - Article
AN - SCOPUS:9944255308
SN - 0168-1923
VL - 127
SP - 159
EP - 173
JO - Agricultural and Forest Meteorology
JF - Agricultural and Forest Meteorology
IS - 3-4
ER -